Character Animation by wpr1947

VIEWS: 13 PAGES: 180

									Character
Animation
                                                          Contents
                                  Character Animation

10 Understanding Character Animation                    167
   Modeling the character        168
   Building, posing, and animating the skeleton   170
   Skinning the skeleton       178
   Using flexors    181
   Animating the character       183
   Workflow summary        184



11 Building Skeletons                  187
   Understanding skeletons        188
        Joints     188
        Joint chains     189
        Limbs      190
        IK handles and IK solvers       191




                                                          Using Maya: Animation   3
Contents


     Creating a joint chain or limb          192
     Viewing a skeleton’s hierarchy               195
     Resizing joint display          195
     Positioning joints        196
     Inserting joints     197
     Removing joints       198
     Mirroring limbs or skeletons            199
     Connecting skeletons            202
     Disconnecting a joint to make two skeletons                     204
     Rerooting the skeleton           205
     Setting joint creation options          206
           Viewing joint creation options          207
           Setting degrees of freedom             208
           Setting automatic joint orientation           208
           Setting scale compensation             210
           Setting automatic joint limits         210
           Setting automatic creation of IK handles                 211
           Setting IK handle options automatically              211
     Editing joint attributes        211
           Viewing editable joint attributes            212
           Renaming a joint          214
           Editing degrees of freedom             216
           Editing a joint’s preferred angle            217
           Editing stiffness      217
           Editing joint orientation        219
           Editing scale compensation             220
           Editing joint limits      220
           Dampening rotation near joint limits               223




4   Using Maya: Animation
                                                                                              Contents



12 Posing and Animating Skeletons                                225
   Understanding posing and animating skeletons                 226
        Forward kinematics          226
        Posing and animating with forward kinematics             228
        Inverse kinematics (IK)           229
        Posing and animating with inverse kinematics (IK)              230
        IK handles and IK chains           230
        IK solvers      231
        Single chain (SC) solver           231
        Rotate plane (RP) solver           233
        Spline solver      237
        Multi-chain (MC) solver           237
   Creating IK handles        238
        Adding an IK handle          238
        Creating an IK chain         239
        Displaying IK handle’s end effector            240
        Displaying IK handle’s goal and goal’s axis            240
        Displaying IK handle’s twist disc and pole vector’s axis             240
   Setting IK handle creation options            241
        Viewing IK handle creation options             241
        Setting the current solver         242
        Activating the multi-chain (MC) solver           243
        Setting autopriority        243
        Setting solver enable        244
        Setting snap enable         244
        Setting sticky     244
        Setting priority      245
        Setting weight        245
        Setting position vs. orientation (PO) weight           246
   Editing IK handle attributes           246
        Viewing editable IK handle attributes           247

                                                                             Using Maya: Animation   5
Contents


           Renaming an IK handle          249
           Editing transform attributes       249
           Editing skeleton info       250
           Editing IK handle attributes       250
           Editing IK solver attributes and choosing an IK solver         251
           Editing pivots     251
           Editing limit information      252
           Editing display    252
           Editing node behavior        253
     Editing IK solvers      253
           Editing IK solver attributes       253
           Editing node behavior        254
     Using IK systems        254
           Creating an IK system        254
           Accessing an IK system         255
           Renaming an IK system          255
           Viewing an IK system’s IK solvers        255
           Editing global snap and global solve       255
           Editing node behavior        256
     Posing IK chains        256
           Posing with single chain (SC) solver IK handles      256
           Positioning with rotate plane (RP) solver IK handles       257
           Twisting with rotate plane (RP) solver IK handles        257
           Eliminating flip in rotate plane (RP) solver IK handles        257
           Sticky posing     258
     Using IK spline handles        259
           Creating IK spline handles         259
           Animating the joint chain         261
           Setting options before creating the IK spline handle       265
           Setting attributes after creating the IK spline handle     271
           Preventing unwanted start joint flipping       272



6   Using Maya: Animation
                                                                                   Contents


        Working with soft body curves          274
   Tips for working with IK spline handles            274
        Working with human skeletons            276
        Working with animal skeletons          277
        Working with sinuous motion on skeletons            278
   Animating IK chains       280
        Keyframing     280
        Motion capture       281



13 Skinning Skeletons                     283
   Understanding skinning          284
        Closest point skinning         284
        Partition set skinning      285
        Skin point set colors      285
        Bind pose    285
        Skin detachment and reattachment              285
   Binding by closest point        285
   Binding by partition set        287
   Binding multiple objects as skin          288
   Returning to bind pose        289
   Displaying skin point set colors          290
   Editing skin point sets       290
   Detaching and reattaching skin            290
        Detaching skin without preserving skin groups and percentages    291
        Detaching skin while preserving skin groups and percentages     292
        Reattaching skin while preserving skin groups and percentages    292




                                                                  Using Maya: Animation   7
Contents


     Animating with skin and skeleton groups                292



14 Using Flexors                     295
     Understanding flexors            296
           Lattice flexors      296
           Sculpt flexors       298
           Cluster flexors      299
     Creating lattice flexors         301
     Positioning lattice flexors after creation            302
     Editing joint lattice flexor attributes     302
           Viewing joint lattice flexor attributes     303
           Renaming joint lattice flexors      303
           Editing creasing       303
           Editing rounding       305
           Editing length in      306
           Editing length out         308
           Editing width left     310
           Editing width right        311
     Editing bone lattice flexor attributes          313
           Viewing bone lattice flexor attributes      313
           Renaming bone lattice flexors       314
           Editing length in      314
           Editing length out         316
           Editing width left     318
           Editing width right        319
           Editing bicep      321
           Editing tricep      322




8   Using Maya: Animation
                                                                  Contents


Creating sculpt flexors    324
Editing sculpt flexor attributes    325
Joint-driven sculpting     325
Creating cluster flexors    326
Editing cluster flexor attributes   328
Editing with cluster flexor manipulators   328




                                                 Using Maya: Animation   9
Contents




10   Using Maya: Animation
10   Understanding Character
     Animation

     As a character animator using Maya, you can create the illusion of life. You
     can animate virtually any character imaginable, no matter how realistic,
     abstract, or surreal. The essence of character animation is timing and motion.
     Maya offers the most sophisticated tools available for defining the timing
     and motion of characters. Using Maya: Animation, Character Animation,




                                                                                      Animation
                                                                                      Character
     describes how to use Maya’s skeleton-based shape deformation tools to
     animate articulated, hierarchical 3D characters with forward or inverse
     kinematics techniques.
     This chapter presents an overview of animating an articulated, hierarchical
     3D character in Maya. Animating a character includes the following:
 •   “Modeling the character” on page 168
 •   “Building, posing, and animating the skeleton” on page 170
 •   “Skinning the skeleton” on page 178
 •   “Using flexors” on page 181
 •   “Animating the character” on page 183
     This chapter concludes with a summary of Maya’s workflow for skeletal
     character animation: “Workflow summary” on page 184.




                                                     Using Maya: Animation     167
Understanding Character Animation
Modeling the character


Modeling the character
                  Modeling is the process of creating a geometry for the character. Modeling is
                  the first step in animating a character.




                  For best results, create the geometry with limbs outstretched. This will make
                  building a skeleton much easier.
                  A geometry can be a non-uniform rational B-spline (NURBS) geometry or a
                  polygonal geometry. A geometry defines the shape of the character’s surface.




168   Using Maya: Animation
                                        Understanding Character Animation
                                                       Modeling the character




                                                                                      Animation
                                                                                      Character
To create a geometry for a character, use the modeling tools in Maya’s
Model menu. When you create the geometry, you should also define how
the character will look when rendered. For rendering, use the tools in
Maya’s Render menu. Note that you can also use Maya’s particle system to
define the character’s features. To use the particle system, use the tools in
Maya’s Dynamics menu.

                                     Note
To use the animation tools this document describes, be sure you have
Maya’s Animation menu selected.

The next step in animating a character is to create a skeleton so you can
control a character’s actions. First you build a skeleton for the character’s
geometry, and then you bind the geometry to the skeleton. This lets you
control the geometry’s shape and actions.




                                                  Using Maya: Animation         169
Understanding Character Animation
Building, posing, and animating the skeleton


Building, posing, and animating the skeleton
                     A skeleton is a structure for animating a character’s articulated, hierarchical
                     actions.




                     The skeleton you build for a character need not exactly resemble what the
                     character’s skeleton would be like in real life. You might create a skeleton for
                     a character that would lack one in real life. Depending on the effect you
                     want to create, you might even have the skeleton influence the geometry
                     from a location outside of the geometry.
                     A skeleton consists of joints connected by the bones of the joints.
                     Additionally, a skeleton can consist of special tools called inverse kinematics
                     (IK) handles. IK handles enable you to pose the character easily, and they
                     facilitate animation.
                     You could begin building a skeleton for a human character by creating some
                     legs.




170    Using Maya: Animation
                                        Understanding Character Animation
                                      Building, posing, and animating the skeleton




                                                                                     Animation
                                                                                     Character
In this example, each leg consists of a simple series of joints connected by
bones. For clarity, these legs are shown without a geometry in the scene.
When you create a skeleton, you should have the geometry in your current
scene so you can be sure the skeleton fits the model properly.
When we think of a real skeleton, we tend to think first of the bones and
then of the joints that enable movement. When it comes to animating
movement, however, we must first focus on the joints and their hierarchical
relationships.
In Maya, the joints of a skeleton always exist in a hierarchy that defines how
they can move in relation to each other. Any two connected joints have a
hierarchical relationship for defining articulated actions. This relationship is
indicated by the bone that connects the two joints.




                                                  Using Maya: Animation      171
Understanding Character Animation
Building, posing, and animating the skeleton



                            Joint

                                                        Bone
                                                                             Joint




                     Note that the bone has a wedge shape. The joint at the thicker end of the
                     wedge is higher in the hierarchy than the joint at the thinner end. Whenever
                     the joint at the thicker end rotates, the bone and the joint at the thinner end
                     will have to move in an arc. But when the joint at the thinner end rotates, the
                     joint at the thicker end will not have to move. This is just like how a real
                     skeleton moves.
                     The joint at the thicker end is called the parent joint in relation to the joint at
                     the thinner end, which is called the child joint. We can think of the parent
                     joint as being “above” the child joint and the child “below” the parent.


                                    Parent joint



                                                                          Child joint



                                                   Parent joint’s
                                                   bone


                     As far as hierarchical movement is concerned, the bone that connects the two
                     joints is really part of the parent joint. A bone belongs to a parent joint,
                     which completely controls the bone’s movements.
                     Note that a joint can have more than one bone, each bone connecting the
                     parent joint to a different child joint.




172    Using Maya: Animation
                                        Understanding Character Animation
                                      Building, posing, and animating the skeleton




                                                                                     Animation
                                                                                     Character
Any simple series of joints connected together by bones is called a joint chain.
The highest joint in the joint chain’s action hierarchy is called the parent joint
of the joint chain. The action of a joint chain’s parent joint affects everything
below it in the chain.


    Parent joint of
    joint chain




You can create very elaborate skeletons consisting of multiple joint chains
organized into a complex hierarchy.
A limb consists of one or more joint chains that branch off from one another
in a tree-like structure.




                                                   Using Maya: Animation      173
Understanding Character Animation
Building, posing, and animating the skeleton




                     The highest joint in a skeleton’s hierarchy is called the root joint; when the
                     root joint moves or rotates, everything must move or rotate with it.
                     The order in which you create joints and their bones defines their action
                     hierarchy for rotation and movement. In the leg, the hip joint is the highest
                     joint in the action hierarchy. The hip joint was created first, then the knee
                     joint, and so on.




174    Using Maya: Animation
                                       Understanding Character Animation
                                     Building, posing, and animating the skeleton




                                                                                    Animation
                                                                                    Character
You can limit how joints rotate so that you can easily put the character in
realistic poses. For example, you can limit how a knee joint can rotate so it
can’t bend from side to side but only forward and back.




                                                 Using Maya: Animation      175
Understanding Character Animation
Building, posing, and animating the skeleton


                     Setting and editing the characteristics of the knee joints will make the
                     animation of a walk cycle much easier. You can set each joint’s
                     characteristics as you create a skeleton and later tweak them as you pose and
                     animate the character.
                     Chapter 11, “Building Skeletons”describes creating and editing joints and
                     bones. After you’ve created all the joints and bones that make up a skeleton
                     for your character, you’ll want to move the skeleton around and put it in
                     various poses.
                     In Maya, there are two basic ways to pose a joint chain: forward kinematics
                     and inverse kinematics.
                     With forward kinematics, when you pose a joint chain you have to specify
                     the rotations of each joint individually, starting from the parent joint on
                     down to all the joints below. This approach is excellent for creating detailed
                     arc motions.
                     With inverse kinematics, when you pose a joint chain all you have to do is
                     tell the lowest joint in the joint chain’s hierarchy where you want it to be,
                     and all the joints above it will rotate automatically. Inverse kinematics offers
                     a very intuitive way to pose a joint chain because it enables goal-directed
                     posing. When you reach for an object, you don’t think about how you are
                     going to rotate your shoulder, your elbow, and so on. You just think about
                     where the object is that you want to reach, and your body automatically
                     does the rest. That’s how inverse kinematics works, too.
                     To pose a joint chain with inverse kinematics, you need to add some special
                     tools to a skeleton. These tools are called inverse kinematics (IK) handles. An IK
                     handle enables you to pose a joint chain intuitively.
                     An IK handle begins at a joint chain’s parent joint and can end at any joint
                     below the parent joint. For example, for each leg you could create an IK
                     handle that controls the joint chain beginning at the hip joint and ending at
                     the ankle joint.




176    Using Maya: Animation
                                       Understanding Character Animation
                                     Building, posing, and animating the skeleton




                                                                                    Animation
                                                                                    Character
You can select the IK handle where it ends at the ankle joint and move the
chain with it in the same way that you would think about moving your own
ankle.
In addition to posing a skeleton, IK handles also play an important role in
the animation of the skeleton. The movement of a chain between the
keyframes of an animation is also automatically solved by the chain’s IK
handles.
IK handles figure out how to rotate and move all the joints in the chain for
you by using an inverse kinematics (IK) solver. An IK solver is the motor
intelligence behind an IK handle. Maya offers several different types of IK
solvers for different types of movement effects. For further control, you can
also specify the characteristics of the IK solvers themselves.
You’ll want to create IK handles for all of a skeleton’s joint chains that you
want to pose. Chapter 12, “Posing and Animating Skeletons” describes how
to use IK handles and IK solvers.
You can pose and animate a skeleton, but such an animation would show
only the timing and motion of a character lacking form and shape. The next
step is to bind the character’s model to the character’s skeleton so that the
skeleton can control the model’s actions.




                                                 Using Maya: Animation      177
Understanding Character Animation
Skinning the skeleton


Skinning the skeleton
                  After you’ve created the character’s geometry and the character’s skeleton,
                  the next step is to bind the two together. When a geometry is bound to a
                  skeleton, the geometry can be referred to as the skeleton’s skin. When you
                  pose the skeleton, the skin moves with the skeleton automatically.




                  The process of binding a geometry to a skeleton is called skinning.
                  NURBS geometries are shaped by points called control vertices (CVs), and
                  polygonal geometries are shaped by points called vertices. In both cases,
                  Maya can control shape by means of points. After a geometry has been
                  bound to a skeleton, these points are called skin points.
                  To bind a geometry to a skeleton, Maya first divides the geometry’s points
                  into sets according to each point’s proximity to a joint. The newly formed
                  skin point sets are identified by various colors. (Note that some expert users
                  call skin point sets partitions because any given point can be in only one set.)
                  Next, Maya binds each skin point set to the nearest joint so the skin points in
                  each skin point set will move with the nearest joint.




178   Using Maya: Animation
                                         Understanding Character Animation
                                                         Skinning the skeleton




                                                                                     Animation
                                                                                     Character
Note that because skin points are bound to joints by means of deformation
tools called joint clusters, expert users sometimes call skin points joint cluster
points.
Once the skin is bound to the skeleton, exercise the character by putting it
into various poses. It’s important to do this because you need to observe
how the skin acts in response to the skeleton’s actions.
Depending on the pose of the geometry and skeleton during binding, a few
of the skin points could join an inappropriate skin point set.




                                                   Using Maya: Animation       179
Understanding Character Animation
Skinning the skeleton




                  If so, you can easily move those skin points from one skin point set to
                  another.




                  Chapter 13, “Skinning Skeletons”describes skinning in more detail.


180   Using Maya: Animation
                                                   Understanding Character Animation
                                                                         Using flexors


Using flexors
         You can animate skin deformation effects by using special deformation tools
         called flexors. Flexors are high-level deformeration tools for use with skins
         and skeletons. The effects of flexors can be driven by how you pose and
         animate a skeleton.
         Maya offers three types of flexors: lattice flexors, sculpt flexors, and cluster
         flexors.
         A lattice flexor influences skin around joints or the bones of joints. It can
         smooth or wrinkle skin around joints, and provide muscle definition around
         bones.
         A sculpt flexor provides anatomically based deformations such as muscle




                                                                                                  Animation
                                                                                                  Character
         bulges, knee caps, and elbow caps. A sculpt flexor can influence skin around
         joints or the bones of joints.
         A cluster flexor controls the points in a skin point set around a joint with
         varying percentages of influence. It can provide very realistic smoothing
         effects.
         Let’s look at a lattice flexor attached to a joint. With a lattice flexor, a joint
         can directly influence skin points, changing the shape of the character’s skin.
         You can create a lattice flexor that will deform skin when the joint it is
         attached to rotates. For example, you can create a flexor that wrinkles the
         skin around an elbow as you bend a character’s arm.




                                                              Using Maya: Animation         181
Understanding Character Animation
Using flexors




                  Similarly, a lattice flexor attached to a bone can influence the skin around a
                  bone. You can use lattice flexors attached to bones for animating muscle
                  definition.




182   Using Maya: Animation
                                                 Understanding Character Animation
                                                               Animating the character


         Chapter 14, “Using Flexors” describes using flexors for skin deformation in
         more detail.
         Using Maya: Animation, Basic Deformers provides further information on
         Maya’s free form deformation tools. Unlike flexors, these deformation tools
         need not work in conjunction with a skeleton. These tools include sculpt
         deformers, wire deformers, lattice deformers, cluster deformers, and blend
         shape deformers. Blend shape deformers, for example, are excellent tools for
         facial animation.
         The time you put into building a skeleton, binding the geometry, and
         creating flexors is time well spent. The effort you put into these steps will
         pay off when you animate the character.




                                                                                               Animation
                                                                                               Character
Animating the character
         The more carefully you design and construct the character, the easier
         animating the character will be. You can animate the character by
         keyframing or by using motion capture data. For general information on
         keyframing animations in Maya, refer to Using Maya: Animation,Keyframe.
         For information on motion capture, see Using Maya, Animation,Motion
         Capture.
         In keyframing, you pose a character in key postures and set these postures
         as keys. Maya then interpolates the actions between the keys for you,
         playing the animation. For example, here is a frame from a walk cycle.




                                                           Using Maya: Animation         183
Understanding Character Animation
Workflow summary




                  When Maya interpolates the actions between keyframes, it uses the IK
                  handles, the IK solvers, the lattice flexors, sculpt flexors, cluster flexors, and
                  all the other attributes of the character that you have defined to produce the
                  animation. Chapter 12, “Posing and Animating Skeletons” describes how to
                  pose and animate skeletons; note that the information there also applies to
                  skeletons with skins. Chapter 13, “Skinning Skeletons” explains how to bind
                  geometries to skeletons for posing and animating characters. Finally,
                  Chapter 14, “Using Flexors” describes posing and animating skin
                  deformations with flexors.


Workflow summary
                  Animating an articulated, hierarchical 3D character in Maya involves using
                  Maya’s skeletal deformation tools: skeletons and flexors. After you create a
                  geometry for the character with Maya’s modeling tools, you can build a
                  skeleton for the geometry and then bind the geometry to the skeleton. This
                  binding process is called skinning. Skinning the geometry to the skeleton
                  binds the model’s shape to the skeleton’s movement. The geometry has
                  become the skeleton’s skin, and the skin’s shape will deform as appropriate
                  when you pose and animate the skeleton. Skeletons can be posed and
                  animated with Maya’s forward or inverse kinematics tools. Special inverse
                  kinematics tools include IK handles and IK solvers.


184   Using Maya: Animation
                                           Understanding Character Animation
                                                            Workflow summary


    In addition to using a skeleton to create skin deformation effects, you can
    also use special deformation tools called flexors. Flexors provide a way for
    you to pose and animate skin deformation effects that complement the
    deformations being provided by the skeleton alone. Flexors are skin shape
    deformation tools whose effects can be driven by the actions of a skeleton.
    For example, the rotation of a joint can drive the bulging of some skin,
    indicating muscle.
    The next chapters cover the following topics:
•   Chapter 11, “Building Skeletons”
•   Chapter 12, “Posing and Animating Skeletons”
•   Chapter 13, “Skinning Skeletons”




                                                                                     Animation
                                                                                     Character
•   Chapter 14, “Using Flexors”




                                                    Using Maya: Animation      185
Understanding Character Animation
Workflow summary




186   Using Maya: Animation
11   Building Skeletons

     After you’ve created a geometry for your character, the next step is to build
     a skeleton for the geometry. In general, you’ll want to have the geometry in
     the scene as you create the skeleton so can be sure the skeleton fits the
     geometry. You could create a character’s skeleton before you create the
     geometry, but you may have to scale the geometry and adjust the skeleton
     before you bind them together.




                                                                                      Animation
                                                                                      Character
     This chapter describes how to build skeletons. Building skeletons includes
     the following:
 •   “Understanding skeletons” on page 188
 •   “Creating a joint chain or limb” on page 192
 •   “Resizing joint display” on page 195
 •   “Positioning joints” on page 196
 •   “Inserting joints” on page 197
 •   “Removing joints” on page 198


                                                     Using Maya: Animation      187
Building Skeletons
Understanding skeletons


                •   “Mirroring limbs or skeletons” on page 199
                •   “Connecting skeletons” on page 202
                •   “Disconnecting a joint to make two skeletons” on page 204
                •   “Rerooting the skeleton” on page 205
                •   “Setting joint creation options” on page 206
                •   “Editing joint attributes” on page 211
                    Note that adding inverse kinematics (IK) handles and using IK solvers are
                    important when animating a skeleton. For information about IK handle and
                    IK solvers, see Chapter 12, “Posing and Animating Skeletons.”

                                                         Note
                    To use the tools for building skeletons, be sure you have Maya’s
                    Animation menu selected.



Understanding skeletons
                    Skeletons are hierarchical, articulated structures for animating geometries.
                    Skeletons provide a basis for animating hierarchical actions in much the
                    same way that a human skeleton determines how the human body can
                    move.
                    When you build a skeleton, the grid can be quite useful for judging the size
                    and shape of the skeleton. You can position and rescale the grid to suit your
                    work. Also, use multiple camera views when building a skeleton to make
                    sure that your skeleton fits the model appropriately in all three dimensions.

Joints
                    Joints are the building blocks of skeletons. Each joint can have one or more
                    bones attached to it. The action of a bone attached to a joint is controlled by
                    the joint’s rotation and movement. Various joint attributes specify how the
                    joint can act. For example, you can specify limitations on how far a joint can
                    rotate.
                    A root joint is the highest joint in a skeleton’s hierarchy. A skeleton can have
                    only one root joint.




188    Using Maya: Animation
                                                                         Building Skeletons
                                                                        Understanding skeletons


               A parent joint is any joint higher in a skeleton’s action hierarchy than any of
               the other joints that are influenced by that joint’s action. Joints below a given
               parent joint in the action hierarchy are called child joints.




                                                Root joint
                                                (selected)




                                                                                                   Animation
                                                                                                   Character
                                             Parent joint
                                             of joint “A”

                                                   Joint “A”


                                                   Bone of
                                                   joint “A”

                                                Child joint of
                                                joint “A”
               Sample skeleton

Joint chains
               A joint chain is any group of joints and their bones connected in a series. The
               joints are connected linearly; you could draw a line through a joint chain’s
               series of joints and their bones without having to retrace your path. A given
               joint chain begins at the highest joint in the joint chain’s action hierarchy.
               This joint is the joint chain’s parent joint.




                                                                 Using Maya: Animation      189
Building Skeletons
Understanding skeletons




                                                                Joint chain


                               Joint chain


                                                                              Joint chain
                                                        Joint chain




                    Joint chains

Limbs
                    A limb is any group of one or more connected joint chains. The chains may
                    branch off from one another, forming a tree-like structure. Unlike a joint
                    chain, a limb’s joints may not be connected linearly; you may not be able to
                    draw a line through all of a limb’s joints and their bones without doubling
                    back. A given limb begins at the highest joint in the limb’s action hierarchy.
                    This joint is the limb’s parent joint.
                    When you begin building a skeleton that will have many symmetrical limbs,
                    start in the center of the workspace near the scene’s world origin. Starting
                    near the center will make it easier for you to create skeletons with many
                    symmetrical parts.




190    Using Maya: Animation
                                                                        Building Skeletons
                                                                       Understanding skeletons




                          Limb

                                             Limb




                                                                                                 Animation
                                                                                                 Character
            Limbs

IK handles and IK solvers
            IK handles are special tools for posing and animating joint chains. On any
            given chain, the joint where the IK handle begins is called the start joint and
            the joint the where IK handle ends is called the end joint. Note that
            experienced users sometimes refer to joint chains that have IK handles as IK
            chains.
            IK solvers provide the motor intelligence of IK handles.
            IK handles and IK solvers are described in Chapter 12, “Posing and
            Animating Skeletons.”
            When you create joint chains and limbs for your character, think about how
            you are going to use IK handles to pose the joint chains. Joint chains that
            consist of four or fewer joints are much easier to pose with IK handles than
            those that have many more joints.




                                                             Using Maya: Animation        191
Building Skeletons
Creating a joint chain or limb


                      Expert users have found that if a skeleton lies entirely in one plane before
                      you bind the geometry to the skeleton, posing the character with IK handles
                      can be somewhat awkward in extreme cases. Having some of the joints
                      rotated slightly at various appropriate angles will make the character easier
                      to pose later on.


Creating a joint chain or limb
                      You begin building a skeleton by creating a joint chain, which is a series of
                      joints and their bones. You can then add to the joint chain by continuing that
                      joint chain or by creating new joint chains starting from any of the joint
                      chain’s joints. In this way you can create a complex structure of various joint
                      chains and limbs. These joint chains and limbs define a skeleton’s action
                      hierarchy. Finally, you can view an outline of a skeleton’s hierarchy. This
                      outline view is useful for getting a clear picture of how your skeleton is
                      structured, and for selecting various parts of the skeleton.

                      To create a joint chain:
                  1   Select Skeletons→Joint Tool.
                  2   Click in the workspace at the position of the first joint.
                      The joint is created.
                      You can set a joint’s attributes while you create the joint or anytime after you
                      have created it. To set a joint’s attributes while you create it, see “Setting
                      joint creation options” on page 206. To modify a joint’s attributes after you
                      have created it, see “Editing joint attributes” on page 211.
                  3   Move the pointer to where you want the second joint, and then click.
                      The two joints are connected with a bone that indicates the direction of the
                      joint chain’s hierarchy: the thinner end of the bone’s triangle points to the
                      child joint.
                  4   Move the pointer to where you want the next joint, and then click. Continue
                      moving the pointer and clicking until you’re done creating the joint chain
                      you want.
                  5   To indicate you’ve finished creating the joint chain, press the Enter key or
                      select another tool.
                      If you want to change the positions of the joints, see “Positioning joints” on
                      page 196.



192    Using Maya: Animation
                                                                 Building Skeletons
                                                          Creating a joint chain or limb




                                                                                             Animation
                                                                                             Character
    Creating a joint chain

    To add to a joint chain:
1   Select Skeletons→Joint Tool.
2   Click on a joint in the joint chain.
    To continue a joint chain, click on the last joint in the joint chain. (The last
    joint is the lowest joint in the joint chain’s hierarchy.)
    To create a new joint chain that branches out from an existing chain, click on
    any joint other than the last joint in an existing chain. A group of one or
    more connected joint chains is called a limb.
3   Click where you want to create a new joint.
4   When you finish creating all the joints in the joint chain, press the Enter key
    or select another tool.




                                                        Using Maya: Animation          193
Building Skeletons
Creating a joint chain or limb



                        Continuing a joint chain




                                                                 1. Click here to
                                                                 continue the
                                                                 joint chain




                                     2. Click to
                                     create more
                                     joints


                                                            or


                           Creating a new joint chain from an existing joint chain




                                     1. Click here
                                     to continue
                                     the joint chain                      2. Click to
                                                                          create more
                                                                          joints




                      Adding to a joint chain



194    Using Maya: Animation
                                                                    Building Skeletons
                                                             Viewing a skeleton’s hierarchy


         You can rapidly build a skeleton for animating a character by continuing
         joint chains and creating new joint chains that branch out from existing joint
         chains.


Viewing a skeleton’s hierarchy
         To view an outline of a skeleton’s hierarchy
         Select Window→Outliner to view an outline of a skeleton’s hierarchy.
         Use the Outliner to see the structure of the skeleton, to select parts of the
         skeleton, and to see the names of the parts of the skeleton.




                                                                                               Animation
                                                                                               Character
Resizing joint display
         You can resize the display of a skeleton’s joints. Increasing the display size
         can make the joints and their bones easier to pick. Decreasing the display
         size can make other objects such as flexors easier to pick.
         Here is a skeleton displayed at normal size:




         Skeleton at normal size
         Here is the same skeleton displayed at 25% of normal size:


                                                           Using Maya: Animation         195
Building Skeletons
Positioning joints




                     Skeleton at 25% normal size

                  To resize joint display:
              1   Select Display→Joint Size.
              2   Move the pointer to the arrow at the end of the Joint Size line.
              3   Choose from the percentages listed to resize the joints, or choose Custom to
                  set your own percentage.
                  Percentages are relative to the default setting, which is always 100% or 1.00.


Positioning joints
                  While you are creating a joint chain, you can edit the positioning of any joint
                  without affecting the joints below it in the joint chain’s action hierarchy.

                                                          Note
                     To edit the position of a joint after the skeleton is created and accepted,
                     toggle on      (the Select by Component Type icon) and            (the Pivot
                     icon), then use the right mouse button on the Pivot button to turn on Joint
                     Pivots in the Pivot pick mask.



196   Using Maya: Animation
                                                                       Building Skeletons
                                                                             Inserting joints


            To position a joint as you create it:
        1   Hold down the left mouse button to create a joint and drag it to a new
            position.
        2   Release the mouse button when you’ve positioned the joint at the desired
            location.

            To position the most recently created joint while creating the joint
            chain:
            While in create mode, you can use the middle mouse button to modify the
            most recent joint (the one currently selected).
            The transform manipulator appears and you can move the joint in any




                                                                                                Animation
                                                                                                Character
            direction.

            To position any joint in the hierarchy while creating a joint chain:
        1   Press Insert on the keyboard.
            The transform manipulator appears at the end joint.
        2   Move any joint in the skeleton by selecting and dragging it with the left
            mouse button.
        3   Press Insert to toggle back to creating more joints for the skeleton. This will
            return you to the last created joint in the chain.


Inserting joints
            You can insert a joint anywhere in a skeleton’s action hierarchy below the
            root joint.

            To insert a joint in a created skeleton:
        1   Select Skeletons→Insert Joint Tool.
        2   To position the new joint, use the left mouse button to drag from the joint
            you want as the new joint’s parent.Until you press Enter or select another
            tool, you can insert more joints.
        3   When you have finished inserting joints, press Enter or select another tool.




                                                              Using Maya: Animation      197
Building Skeletons
Removing joints




                        1. Click to
                        add a joint
                        below this one
                                                                       2. Drag to
                                                                       position the
                                                                       new joint




                     Inserting a joint


Removing joints
                  You can remove any joint from a skeleton except the root joint. The root joint
                  is the highest joint in a skeleton’s action hierarchy, and deleting the root joint
                  would delete the entire skeleton.

                  To remove a joint:
              1   Select the joint you want to remove.
                  Note that you can only remove one joint at a time.
              2   Select Skeletons→Remove Joint.
                  The joint is removed. The bone of the joint above the removed joint is
                  extended to the joint below the removed joint.




198   Using Maya: Animation
                                                                    Building Skeletons
                                                               Mirroring limbs or skeletons




                                                                  Bone is
              Click to                                            resized
              delete the joint




                                                                                              Animation
                                                                                              Character
         Removing a joint


Mirroring limbs or skeletons
         A group of one or more connected joint chains is called a limb. You can
         duplicate or make mirror copies of limbs. A mirror copy is a copy that is
         symmetrical about a selected plane; in effect, the reflection of the original in
         the plane is turned into a real copy of the original, but with all the aspects of
         the limb mirrored accordingly. The origin of the plane is at the parent joint
         of the limb. Joint attributes and IK handles are mirrored as well as the joints
         and their bones.
         Mirroring is extremely useful when you are creating the limbs for a
         character. For example, you can build a right arm and hand, and then create
         a mirrored copy of it for the left arm and hand. Mirroring affects all aspects
         of the creation of the left arm, including the joint limits. You don’t have to
         reset the joint limits so that the left arm’s joint limits will be symmetrical to
         the right arm’s joint limits; Maya will do it for you.
         You can also make a mirror copy of an entire skeleton. The procedure is the
         same as for creating mirror copies of limbs, except that the skeleton will be
         mirrored about the scene’s world origin.




                                                            Using Maya: Animation      199
Building Skeletons
Mirroring limbs or skeletons




                                    1. Click here to
                                    mirror this limb




                                                       2. A mirror copy
                                                       of the limb is
                                                       created




                      Mirroring a limb




200    Using Maya: Animation
                                                               Building Skeletons
                                                          Mirroring limbs or skeletons




             Click the root                Skeleton is
             to mirror the                 mirrored about the
             whole skeleton                world origin




                                                                                         Animation
                                                                                         Character
    Mirroring a skeleton

    To mirror a limb or skeleton:
1   Select the parent joint of the limb you want to duplicate, or select the root
    joint if you want to mirror an entire skeleton.
2   To choose the plane for mirroring, first select Skeletons→Mirror Joint-Ë to
    open the Mirror Joint Options window. Next, click the desired Mirror
    Across option to choose the plane in which you want the joint chain
    mirrored.
    The default is XY. If you are mirroring a limb, this indicates the XY plane
    whose origin is at the limb’s parent joint. If you are mirroring a skeleton, this
    indicates the XY plane whose origin is the scene’s world origin.
3   Click Mirror in the Mirror Joint Options window, or select
    Skeletons→Mirror Joint.
    If you are mirroring a limb, the limb is mirrored across the selected plane
    whose origin is at the limb’s parent joint.
    If you are mirroring a skeleton, the skeleton is mirrored across the selected
    plane whose origin is the scene’s world origin.




                                                      Using Maya: Animation       201
Building Skeletons
Connecting skeletons


Connecting skeletons
                   You can connect two skeletons in two ways: by combining joints and by
                   connecting joints with a bone.
                   First, you can connect two skeletons by combining the root joint of one
                   skeleton with any joint of another skeleton except that skeleton’s root joint.
                   The skeleton that becomes a limb of the other skeleton will change its
                   position in the scene so that it is directly connected to the other skeleton’s
                   joint.
                   Second, you can connect the root joint of one skeleton to any joint of another
                   skeleton by extending a bone to the root joint from the joint of the other
                   skeleton. The skeleton that becomes a limb of the other skeleton will not
                   have to move.

                   To connect skeletons by combining joints:
               1   Select the root joint of the skeleton you want to be a limb of another
                   skeleton.
               2   On the other skeleton, select any joint other than the skeleton’s root joint.
               3   Select Skeletons→Connect Joint-Ë.
                   The Connect Joint Options window is displayed.
               4   In the Connect Joint Options window, turn on the Connect Joint mode.
                   The skeleton that will become the limb moves so that its root is in the same
                   place as the selected joint of the other skeleton.
               5   In the Connect Joint Options window, click Connect. (Alternatively, select
                   Skeletons→Connect Joint.)
                   The two skeletons are connected.




202   Using Maya: Animation
                                                               Building Skeletons
                                                                Connecting skeletons




         Two joints are
         combined




                                                                                          Animation
                                                                                          Character
    Connecting skeletons by combining joints

    To connect skeletons by connecting joints with a bone:
1   Click the root of the skeleton you want to be a limb of another skeleton.
2   On the other skeleton, select any joint other than the skeleton’s root joint.
    You can connect only to a non-root joint of the parent skeleton.
3   Select Skeletons→Connect Joint-Ë.
    The Connect Joint Options window is displayed.
4   In the Connect Joint Options window, turn on the Parent Joint mode.
    Parent Joint mode connects the skeletons by creating a new bone between
    the selected root joint and the joint you’re connecting it to. The two skeletons
    do not move.
5   In the Connect Joint Options window, click Connect. (Alternatively, select
    Skeletons→Connect Joint.)
    Maya connects the skeletons with a bone.
    Note that connecting skeletons using Parent Joint mode is identical to the
    result you get by selecting Edit→Parent.



                                                      Using Maya: Animation         203
Building Skeletons
Disconnecting a joint to make two skeletons




                                        Bone created
                                        to connect the
                                        two skeletons




                      Connecting two skeletons by connecting joints with a bone


Disconnecting a joint to make two skeletons
                     You can break up a skeleton into two skeletons by disconnecting any joint
                     other than the root joint. The disconnected joint will become the root joint of
                     the new skeleton.
                     Note that if you disconnect a joint in a joint chain that has an IK handle, that
                     IK handle will be deleted. For information about IK handles, see Chapter 12,
                     “Posing and Animating Skeletons.”




204    Using Maya: Animation
                                                                       Building Skeletons
                                                                       Rerooting the skeleton




                         Select joint you
                         want to
                         disconnect




                                                                                                Animation
                                                                                                Character
           Disconnecting a joint

           To disconnect a joint to make two skeletons:
       1   Select the joint you want to disconnect. This joint will become the root joint
           of the new skeleton.
       2   Select Skeletons→Disconnect Joint.
           The joint is disconnected. The disconnected joint is now the root joint of the
           new skeleton.


Rerooting the skeleton
           You can change the hierarchical organization of a skeleton by changing
           which joint is the root joint. This process is called rerooting.
           Note that any IK handles that pass through the joint selected to be the new
           root joint will be deleted. Also, any animation of the skeleton’s root joint will
           be affected when you reroot.




                                                             Using Maya: Animation      205
Building Skeletons
Setting joint creation options




                  Current root
                  joint




                                                                  Click to
                                                                  create new
                                                                  root joint




                       Rerooting a skeleton

                      To reroot a skeleton:
                  1   Click the joint where you want the new root.
                      If you select the child of the entire joint chain, the hierarchy will reverse.
                      If you select a joint in the middle of the skeleton to become the new root, you
                      will have two child joints with separate hierarchies below the root joint.
                  2   Select Skeletons→Reroot Skeleton.


Setting joint creation options
                      A joint’s various options and attributes define how a joint can be posed and
                      animated. Specifying these is an important part of building a skeleton. You
                      can set joint creation options before you create individual joints, or you can
                      edit a joint’s attributes at any time after you have created it.
                      This section describes how to set joint attributes automatically by setting the
                      Joint Tool’s Tool Settings. To find out how to edit joint attributes, see
                      “Editing joint attributes” on page 211.
                      Setting joint attributes during joint creation includes:


206    Using Maya: Animation
                                                                         Building Skeletons
                                                                  Setting joint creation options


         •   Viewing joint creation options
         •   Setting degrees of freedom
         •   Setting automatic joint orientation
         •   Setting scale compensation
         •   Setting automatic joint limits
         •   Setting automatic creation of IK handles
         •   Setting IK handle options automatically

Viewing joint creation options
             When you create a joint, you use the Joint Tool. You can set the Joint Tool’s




                                                                                                   Animation
                                                                                                   Character
             options so that certain joint options and attributes will be set automatically.
             The Joint Tool’s options are displayed in the Joint Tool’s Tool Settings
             window.




             Tool Settings window

             To view joint creation options:
             Select Skeletons→Joint Tool-Ë.
             The Joint Tool’s Tool Settings window is displayed.


                                                               Using Maya: Animation       207
Building Skeletons
Setting joint creation options


Setting degrees of freedom
                      Each joint has a local axis whose origin is at the center of the joint. The X-axis
                      of the local axis is red, the Y-axis is green, and the Z-axis is blue. How a joint
                      can rotate is defined in terms of this local axis.
                      A joint’s degrees of freedom specifies which of its local axes it can rotate
                      about during IK posing and animation.During IK, a joint is rotated by an IK
                      handle, and how the IK handle performs depends on the type of IK solver
                      the IK handle is using.
                      A joint can have at most three degrees of freedom: the freedom to rotate
                      about its X-axis, Y-axis, and Z-axis during IK. Expert users often call a joint
                      with three degrees of freedom a ball joint because it can rotate about all three
                      of its axes like a ball.
                      Note that two types of IK solvers, the single chain solver and the plane
                      solver, require that their start joints be ball joints that have no limitations on
                      the extent they can rotate about each axis.
                      You can limit a joint so that it has only two degrees of freedom or only one
                      degree of freedom. A joint with two degrees of freedom can only rotate
                      about any two of its local axes during IK. A human wrist would be a good
                      example of a joint with two degrees of freedom, though the joint has
                      limitations on the extent it can rotate about its axes. A joint with only one
                      degree of freedom can rotate only about its local X-axis, or Y-axis, or Z-axis
                      during IK. Expert users often call a joint with only one degree of freedom a
                      hinge joint. A human knee would be a good example of a hinge joint.

                      To set degrees of freedom:
                  1   Select Skeletons→Joint Tool-Ë.
                      The Tool Settings window is displayed.
                  2   In the Tool Settings window, click the X, Y, and Z, Degrees of Freedom
                      check boxes to select the joint’s degrees of freedom.

Setting automatic joint orientation
                      Maya can set the orientation of a joint’s local axis automatically. You can
                      have the joint’s local axis oriented relative to the joint’s first child joint, or
                      you can have the joint’s local axis oriented relative to the scene’s world axis.
                      The orientation of a joint’s local axis is largely a matter of personal




208    Using Maya: Animation
                                                                  Building Skeletons
                                                           Setting joint creation options


    preference. Some expert users like to have the local axis of joints
    automatically orient towards first child joints, and other expert users prefer
    to have the local axis initially oriented the same as the scene’s world axis.
    By default, the orientation of a joint’s local axis is xyz. In this orientation, the
    positive X-axis points in the same direction as the joint’s wedge-shaped
    bone. That is, the X-axis points towards the center of the joint’s child joint. If
    the joint has more than one child joint, the X-axis points at the child joint that
    was created first. The Z-axis points sideways from the joint and its bone
    connecting the child joint, and the Y-axis points at right angles to the X-axis
    and Z-axis. All three axes are aligned according to the right hand rule.
    For example, in a human skeleton the elbow joint’s X-axis would be pointing
    towards the wrist joint. With the arm lying flat, the elbow joint could twist




                                                                                            Animation
                                                                                            Character
    about most of the X-axis, turning the rest of the arm. The elbow joint could
    partially swing up and down about the Z-axis, but it would not be able to
    pivot about the Y-axis.
    You can select various combinations of the X-, Y-, and Z-axes to specify the
    orientation of a joint’s local axis. The first axis in the combination is the axis
    that points at the joint’s first child joint. The third axis points sideways from
    the joint and its bone connecting the child joint, and the second axis points at
    right angles to the first axis and third axis. All three axes are aligned
    according to the right hand rule. In terms of yaw, pitch, and roll, rotation
    about the first axis produces roll, rotation about the second axis produces
    yaw, and rotation about the third axis produces pitch.
    Instead of orienting the joint’s local axis relative to the first child joint, you
    can set the local axis to have the same orientation as the scene’s world axis.
    In this case, the orientation would be set to “none.”

    To set automatic joint orientation:
1   Select Skeletons→Joint Tool-Ë.
    The Tool Settings window is displayed.
2   In the Tool Settings window, select one of the Auto Joint Orient options.
    Note that None orients the joint to the scene’s world axis.




                                                        Using Maya: Animation       209
Building Skeletons
Setting joint creation options


Setting scale compensation
                      When you scale the size of a joint, you can either scale the child joints also or
                      prevent the scaling of the child joints. For example, if you increase the length
                      of a lower arm bone by scaling the elbow joint, the wrist joint and its bones
                      can either increase in size also or stay the same size. Either you can scale the
                      hand as well as the lower arm or you can just scale the lower arm.
                      Normally, when you scale a joint Maya will scale everything below it in the
                      skeleton’s action hierarchy. However, by setting a joint’s Scale Compensate
                      option on, you can prevent that joint and everything below it in the action
                      hierarchy from being scaled when the joint’s parent joint is scaled.
                      Additionally, expert users like to have Scale Compensate on to prevent
                      inappropriate shearing deformation effects on a character’s skin. Shearing
                      can occur when a given joint is scaled only along one or two of its axes.

                      To set scale compensation:
                  1   Select Skeletons→Joint Tool-Ë.
                      The Tool Settings window is displayed.
                  2   In the Tool Settings window, click the Scale Compensate check box on or
                      off.

Setting automatic joint limits
                      You can have Maya automatically limit the extent a joint can rotate about its
                      axes according to the angles at which you build the skeleton’s joints. With
                      Auto Joint Limits on, the smaller inner angle of a joint rounded off to 180
                      degrees is set as the allowable range of rotation. For example, when you are
                      creating a knee joint, if you create the joint slightly bent back, the joint will
                      automatically not be able to swing the lower leg bone forward of the upper
                      leg bone, nor will it be able to wobble from side to side. The joint will not be
                      able to rotate in any other way except through the inner angle rounded off to
                      180 degrees. However, note that this limitation does not change the joint’s
                      Degrees of Freedom setting.

                      To set automatic joint limits:
                  1   Select Skeletons→Joint Tool-Ë.
                      The Tool Settings window is displayed.
                  2   In the Tool Settings window, click the Auto Joint Limits check box on or off.


210    Using Maya: Animation
                                                                          Building Skeletons
                                                                         Editing joint attributes


Setting automatic creation of IK handles
             Maya can automatically create an IK handle for you when you finish
             creating a joint chain. The joint chain’s parent joint will become the IK
             handle’s start joint, and the last joint in the joint chain will become the IK
             handle’s end joint.

             To set automatic creation of IK handles:
         1   Select Skeletons→Joint Tool-Ë.
             The Tool Settings window is displayed.
         2   In the Tool Settings window, click the Create IK Handle check box on or off.




                                                                                                    Animation
                                                                                                    Character
Setting IK handle options automatically
             See Chapter 12, “Posing and Animating Skeletons,” for descriptions of the IK
             handle options you can set when you create IK handles.

             To set joint attributes:
         1   Select Skeletons→Joint Tool-Ë.
             The Tool Settings window is displayed.
         2   In the Tool Settings window, select IK Handle Options.


Editing joint attributes
             A joint’s attributes can be set automatically when you create the joint, or you
             can edit a joint’s attributes at any time. This section describes how to edit
             joint attributes with the Attribute Editor. For more information on using the
             Attribute Editor, please see Using Maya: Maya Basics, Building Objects and
             Scenes, Chapter 5, “Working with General Editors.”
             To find out how to set joint attributes automatically, see “Setting joint
             creation options” on page 206.
             Editing a joint includes:
         •   Viewing editable joint attributes
         •   Renaming a joint
         •   Editing degrees of freedom



                                                                Using Maya: Animation         211
Building Skeletons
Editing joint attributes


                  •    Editing stiffness
                  •    Editing a joint’s preferred angle
                  •    Editing joint orientation
                  •    Editing scale compensation
                  •    Editing joint limits
                  •    Dampening rotation near joint limits
                       You can access settings for a joint’s attributes, and also the Attribute Editor,
                       by pressing the right mouse button while the cursor is on the joint you want
                       to edit.

Viewing editable joint attributes
                       To view or edit a joint’s attributes, use the Attribute Editor.




212    Using Maya: Animation
                                      Building Skeletons
                                     Editing joint attributes




                                                                Animation
                                                                Character




Attribute Editor for joints


                              Using Maya: Animation     213
Building Skeletons
Editing joint attributes


                       To view editable joint attributes:
                       Choose Window→Attribute Editor to open the Attribute Editor.
                       The Attribute Editor is displayed.

Renaming a joint
                       Maya names joints for you when you create them. By default, joints are
                       numbered consecutively as you create them. However, you can rename the
                       joints to better reflect their purpose in your character’s skeleton. It’s a good
                       idea to give joints meaningful names so they are easier to select when you
                       are working with Maya’s editors, using the Hypergraph, or using the
                       Outliner.

                       To rename a joint:
                  1    Select the joint.
                  2    Choose Window→Attribute Editor to open the Attribute Editor.
                  3    Enter the new name in the joint: field.
                       The new name takes effect immediately.




214    Using Maya: Animation
                                                      Building Skeletons
                                                     Editing joint attributes




                                                                                Animation
                                                                                Character




Examples of meaningful joint names in the Outliner




                                             Using Maya: Animation      215
Building Skeletons
Editing joint attributes


Editing degrees of freedom
                       Each joint has a local axis whose origin is at the center of the joint. The X-axis
                       of the local axis is red, the Y-axis is green, and the Z-axis is blue. How a joint
                       can rotate is defined in terms of this local axis.
                       A joint’s degrees of freedom specifies which of its local axes it can rotate
                       about during inverse kinematics (IK) posing and animation. During IK, a
                       joint is rotated by an IK handle, and how the IK handle performs depends
                       on the type of IK solver the IK handle is using.
                       A joint can have at most three degrees of freedom: the freedom to rotate
                       about its X-axis, Y-axis, and Z-axis during IK. Expert users often call a joint
                       with three degrees of freedom a ball joint because it can rotate about all three
                       of its axes like a ball.
                       Note that two types of IK solvers, the single chain solver and the plane
                       solver, require that their start joints be ball joints that have no limitations on
                       the extent they can rotate about each axis.
                       You can limit a joint so that it has only two degrees of freedom, or only one
                       degree of freedom. A joint with two degrees of freedom can only rotate
                       about any two of its local axes during IK. A human wrist would be a good
                       example of a joint with two degrees of freedom, though the joint has
                       limitations on the extent it can rotate about its axes. A joint with only one
                       degree of freedom can rotate only about its local X-axis, or Y-axis, or Z-axis
                       during IK. Expert users often call a joint with only one degree of freedom a
                       hinge joint. A human knee would be a good example of a hinge joint.
                       Note that you can have a joint’s degrees of freedom set automatically when
                       you create the joint. To find out how to set a joint’s degrees of freedom
                       automatically, see “Setting degrees of freedom” on page 208.

                       To edit a joint’s degrees of freedom:
                  1    Select the joint.
                  2    Choose Window→Attribute Editor to open the Attribute Editor.
                  3    In the Attribute Editor, click the X, Y, and Z Degrees of Freedom check
                       boxes to select the joint’s degrees of freedom.




216    Using Maya: Animation
                                                                            Building Skeletons
                                                                           Editing joint attributes


Editing a joint’s preferred angle
              This attribute influences how an IK handle will prefer to rotate a joint during
              inverse kinematics. If you are not familiar with inverse kinematics (IK), IK
              handles, and IK solvers, see Chapter 12, “Posing and Animating Skeletons.”
              The IK solver often can rotate a joint in a number of different ways in order
              to reach the goal. Similarly, when more than one IK handle passes through a
              joint, the first priority of all the IK solvers is to make all the IK handles reach
              their goals. Often a variety of joint rotations can allow the IK handles to
              reach their goals.
              Depending on how you want your character to move, some rotations are
              more appropriate than others. You can identify preferred angles for your




                                                                                                      Animation
                                                                                                      Character
              character’s actions. Two types of IK solvers, the single chain IK solver and
              the rotate plane IK solver, will then give those angles priority over other
              possible angles during joint rotation. The angles you give priority to are
              called preferred angles.
              Preferred angles can enable smoother motion during animation.

              To edit a joint’s preferred angle:
          1   Select the joint.
          2   Choose Window→Attribute Editor to open the Attribute Editor.
          3   Use the Preferred Angle fields to set the angle you prefer the joint to be in.
              The three values refer to the X, Y, and Z axes respectively. The angles are
              relative to the local coordinate system of the joint.

Editing stiffness
              This attribute influences how stiffly an IK handle can rotate a joint during
              inverse kinematics. If you are not familiar with inverse kinematics (IK), IK
              handles, and IK solvers, see Chapter 12, “Posing and Animating Skeletons.”
              When you use inverse kinematics to move a joint chain for animation, you
              can set some joints to move less freely than others. You can set joints in the
              mid-back of a human to move and bend less freely than those in the lower
              back, for example. The resistance to movement of a particular joint is called
              its stiffness.




                                                                  Using Maya: Animation       217
Building Skeletons
Editing joint attributes


                       Stiffness operates relatively between joints in a joint chain controlled by IK
                       handles. IK solver calculations for stiffness can require a little more time
                       than usually required, so use stiffness only when its effect is particularly
                       important.
                       You set the stiffness for each axis separately. You can use this for joints that
                       move in several directions. For example, a wrist joint moves more freely
                       bending toward the forearm than it does from side to side.




      Set stiffness
      high in Z-axis                                      Set stiffness
                                                          low in X-axis




                       Set stiffness to create realistic animation
                       Expert users have found that when stiffness is specified, the solver adjusts
                       the internal energy strictly under the constraint that the end effectors stay
                       fixed. Therefore, if there are no redundant degrees of freedom, the stiffness
                       won’t modify the single chain IK solver’s solution.

                       To edit a joint’s stiffness
                  1    Select the joint.
                  2    Choose Window→Attribute Editor to open the Attribute Editor.
                  3    In the Stiffness fields, enter values from 0 to 100.0 for the X-, Y-, and Z-axes.
                       The X-, Y-, and Z-axes are in the local coordinate system. 0 means the joint
                       moves freely, 50 is moderately stiff, and 100 fuses the joint so that it’s
                       immovable.
                       With stiffness set to 0, no stiffness is specified. This is the recommended
                       setting unless creating the effect of stiffness is particularly important.


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Editing joint orientation
              You can edit the orientation of a joint’s local axis. You can have the joint’s
              local axis oriented relative to the joint’s first child joint, or you can have the
              joint’s local axis oriented relative to the scene’s world axis. The orientation of
              a joint’s local axis is largely a matter of personal preference. Some expert
              users like to have the local axis of joints automatically orient towards first
              child joints, and other expert users prefer to have the local axis initially
              oriented the same as the scene’s world axis.
              By default, the orientation of a joint’s local axis is xyz. In this orientation, the
              positive X-axis points in the same direction as the joint’s wedge-shaped
              bone. That is, the X-axis points towards the center of the joint’s child joint. If
              the joint has more than one child joint, the X-axis points at the child joint that




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                                                                                                      Character
              was created first. The Z-axis points sideways from the joint and its bone
              connecting the child joint, and the Y-axis points at right angles to the X-axis
              and Z-axis. All three axes are aligned according to the right hand rule.
              For example, in a human skeleton the elbow joint’s X-axis would be pointing
              towards the wrist joint. With the arm lying flat, the elbow joint could twist
              about most of the X-axis, turning the rest of the arm. The elbow joint could
              partially swing up and down about the Z-axis, but it would not be able to
              pivot about the Y-axis.
              You can select various combinations of the X-, Y-, and Z-axes to specify the
              orientation of a joint’s local axis. The first axis in the combination is the axis
              that points at the joint’s first child joint. The third axis points sideways from
              the joint and its bone connecting the child joint, and the second axis points at
              right angles to the first axis and third axis. All three axes are aligned
              according to the right hand rule. In terms of yaw, pitch, and roll, rotation
              about the first axis produces roll, rotation about the second axis produces
              yaw, and rotation about the third axis produces pitch.
              Instead of orienting the joint’s local axis relative to the first child joint, you
              can set the local axis to have the same orientation as the scene’s world axis.
              In this case, the orientation would be set to “none.”

              To edit a joint’s orientation:
          1   Select the joint.
          2   Choose Window→Attribute Editor to open the Attribute Editor.
          3   Enter new values in the Joint Orient fields.
              The three values refer to the X-, Y-, and Z-axes respectively.


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Editing scale compensation
                       When you scale the size of a joint, you can either scale the child joints also or
                       prevent the scaling of the child joints. For example, if you increase the length
                       of a lower arm bone by scaling the elbow joint, the wrist joint and its bones
                       can either increase in size also or stay the same size. Either you can scale the
                       hand as well as the lower arm or you can just scale the lower arm.
                       Normally, when you scale a joint Maya will scale everything below it in the
                       skeleton’s action hierarchy. However, by setting a joint’s Scale Compensate
                       option on, you can prevent that joint and everything below it in the action
                       hierarchy from being scaled when the joint’s parent joint is scaled.
                       Additionally, expert users like to have Scale Compensate on to prevent
                       inappropriate shearing deformation effects on a character’s skin. Shearing
                       can occur when a given joint is scaled only along one or two of its axes.

                       To edit a joint’s scale compensation:
                  1    Select the joint.
                  2    Choose Window→Attribute Editor to open the Attribute Editor.
                  3    Toggle Segment Scale Compensate.
                       Turn on Segment Scale Compensate so that this joint will compensate for
                       scale factors applied to its parent. If the parent is scaled, this joint’s
                       translation values will be scaled but the scale will not apply to any of this
                       joint’s children.

Editing joint limits
                       You can restrict a joint to a certain range of motion so that it cannot rotate
                       beyond the angles you set as limits. You set these limits in the Limit
                       Information panel of the Attribute Editor for joints.
                       Expert users have found that it is best to not set joint minimum and
                       maximum limits extremely close (±5 degrees or less). These restrictive limits
                       can sometimes cause joints to get stuck during rotation.

                       To edit joint limits:
                  1    Select the joint.
                  2    Choose Window→Attribute Editor to open the Attribute Editor.




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3   Toggle on the boxes by the Min and Max limits of any value you want to
    change.
    For example, to set minimum and maximum limits for rotation in X, click the
    boxes to the left and right of Rot Limit X.
4   In the Limit X, Y, and Z fields under Translate, Rotate, and Scale, enter the
    angles between which you want to limit the joint’s motion.




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                                       Range of
                                       motion if
                                       the Z-axis
                                       rotation
                                       limits are
                                       set to -15,
                                       45




                                                Range of
                                                motion if
                                                the X-axis
                                                rotation
                                                limits are
                                                set to -45,
                                                90

                       Restricting joint rotation with the Limits attributes




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Dampening rotation near joint limits
             For most living creatures, when a joint rotates as far as it can, it tends to slow
             down or “dampen” before reaching its limit. For example, an elbow does not
             snap straight, but gradually slows down as the lower arm aligns with the
             upper arm. In animation terminology, the effect is that of an “ease-in.”
             Joint dampening applies resistance to a joint as it approaches its joint limits.
             Instead of the joint abruptly stopping when it reaches its limits, you can use
             damping to slow it down smoothly. Depending on the strength and range
             you set, a joint with dampening will not reach its limit boundary, unless
             forced.
             The dampening factor for joints affects only the solution computed by an IK




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                                                                                                    Character
             solver; it does not affect joints that are animated by other means.
             Two settings in the Attribute Editor control a joint’s dampening: Damp
             Range and Damp Strength.
         •   Minimum and Maximum Rotate Damp Range set the number of degrees
             inside the joint limits at which resistance begins to occur.
         •   Minimum and Maximum Rotate Damp Strength set the amount of
             resistance in the damp range.




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                                                                 Minimum
                                                                 damp range
                                                  Maximum
                                                  damp range
                                                                          Maximum damp
                                                                          strength affects
                               Maximum damp
                                                                          this area
                               strength affects
                               this area
                                                                     Minimum Z-
                                                                     axis joint
                                                    Maximum Z-       limit (-15)
                                                    axis joint
                                                    limit (45)


                       Damping the limits of a right wrist joint in the Z-axis

                       To dampen rotation near joint limits:
                  1    Select the joint.
                  2    Choose Window→Attribute Editor to open the Attribute Editor.
                  3    Use the Min and Max Rotate Damp Range and Rotate Damp Strength
                       fields to set the joint dampening attributes.
                       The Rotate Damp Range values let you set the angles inside the minimum
                       and maximum joint limits.
                       The Rotate Damp Strength of the resistance can range from 0, which takes
                       the joint all the way to its limit with no resistance, to 100, which stops the
                       joint at the outer edge of the damp range.
                       The values are relative within the IK handle’s joint chain.




224    Using Maya: Animation
12   Posing and Animating
     Skeletons

     After you’ve created a skeleton for your character, you skin the skeleton by
     binding the geometry to the skeleton. You can then create flexors for further
     skin deformation effects. Animating the character includes animating the
     skeleton and animating the effects provided by the flexors.




                                                                                     Animation
                                                                                     Character
     This chapter describes posing and animating skeletons. Posing and
     animating skeletons includes the following:
 •   “Understanding posing and animating skeletons” on page 226
 •   “Creating IK handles” on page 238
 •   “Setting IK handle creation options” on page 241
 •   “Editing IK handle attributes” on page 246
 •   “Editing IK solvers” on page 253
 •   “Using IK systems” on page 254
 •   “Posing IK chains” on page 256

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                •   “Using IK spline handles” on page 259
                •   “Animating IK chains” on page 280


Understanding posing and animating
skeletons
                    When you pose and animate a skeleton, you are specifying the skeleton’s
                    motion. The term for the specification of motion is kinematics. Posing and
                    animating skeletons involves two types of kinematics: forward kinematics
                    and inverse kinematics. Although the terms sound complicated, what they
                    refer to is easy to understand. Forward kinematics is ideal for creating
                    detailed arc motions because it requires the direct specification of each joint
                    rotation. Inverse kinematics is ideal for creating goal-directed motion
                    because it only requires the specification of a position and orientation that
                    the joints in a joint chain will rotate to reach.

Forward kinematics
                    In forward kinematics, when you pose a joint chain you rotate each joint
                    individually. For example, if you want a joint chain to reach for a particular
                    location in space, you have to rotate each joint individually so that the joint
                    chain can reach the location. To do this, you would rotate the joint chain’s
                    parent joint, then the next joint, and so on down the joint chain. When you
                    animate a skeleton posed with forward kinematics, Maya interpolates the
                    joint rotations starting with the root joint, then the root’s child joints, and so
                    on down through the skeleton’s action hierarchy. Maya proceeds “forward”
                    through the action hierarchy, starting at the root joint.
                    Posing and animating skeletons with forward kinematics is an excellent
                    approach for specifying detailed arc motions, but it can take a fair amount of
                    time if you are animating a large, complicated skeleton. Also, forward
                    kinematics is often not very intuitive for specifying goal-directed motion.
                    When you think about moving your hand to some location in space, you
                    don’t normally think about how you are going to rotate all the joints in your
                    arm.
                    The following sequence of five images illustrates the steps required to
                    extend a W-shaped joint chain with forward kinematics posing.




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Forward kinematics posing: joint chain’s root joint selected




                                                                                Animation
                                                                                Character
Forward kinematics posing: root joint rotation




Forward kinematics posing: subsequent joint rotation




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                     Forward kinematics posing: subsequent joint rotation




                     Forward kinematics posing: joint chain extended

Posing and animating with forward kinematics
                    To pose a skeleton with forward kinematics, you move, rotate, or scale joints
                    directly. You can do this in the same way that you move, rotate, or scale
                    other objects in Maya. For example, you can use the move, rotate, and scale
                    transform tools in the minibar. Alternatively, you could move, rotate, and
                    scale joints by using the Channel Box.
                    To animate a skeleton with forward kinematics, you can save keys in
                    selected frames as described in Using Maya: Animation, Keyframe. If you
                    would like to use motion capture data to drive the character animation, see
                    Using Maya: Animation, Motion Capture.
                    This chapter focuses on posing and animating with Maya’s inverse
                    kinematics tools.


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Inverse kinematics (IK)
            In inverse kinematics (IK), you can pose a joint chain based on a location in
            space you want the joint chain to reach. Inverse kinematics is more intuitive
            for goal-directed motion than forward kinematics because you can focus on
            the goal you want a joint chain to reach without worrying about how each
            joint will have to rotate. However, unlike forward kinematics, inverse
            kinematics requires that you use special tools for posing and animating.
            These tools are called IK handles and IK solvers.
            An IK handle is like a wire that can run through a joint chain, providing a
            way for you to pose the entire joint chain in one action. As you pose and
            animate the joint chain with the IK handle, the IK handle automatically
            figures out how to rotate all the joints in the joint chain by using its IK




                                                                                             Animation
                                                                                             Character
            solver.
            The IK solver is the motor intelligence behind the IK handle. For example, if
            you want a joint chain to reach a particular location in space, you can move
            the entire chain by using the IK handle that runs through the chain. Given
            where you want the joint chain to reach, the IK solver figures out how to
            rotate all the joints in the joint chain for you by means of Maya’s inverse
            kinematics methods.
            The following sequence of two images illustrates the steps required to
            extend a W-shaped joint chain with inverse kinematics posing.




            Inverse kinematics posing: IK handle selected




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                     Inverse kinematics posing: joint chain extended

Posing and animating with inverse kinematics (IK)
                    To pose and animate joint chains with inverse kinematics, you use IK
                    handles. The motor intelligence of an IK handle is provided by an IK solver.

IK handles and IK chains
                    An IK handle runs through a selected joint chain like a wire, providing you
                    with a way to move the entire joint chain. The joint the IK handle starts at is
                    called the start joint. The last joint in the joint chain controlled by the IK
                    handle is called the end joint. The start joint could be the skeleton’s root joint,
                    or any joint in the skeleton’s action hierarchy above the end joint. The IK
                    handle can pose all the joints in the chain, from the start joint to the end
                    joint. A joint chain that has an IK handle is called an IK chain. IK chains are
                    easy to use. However, some background on how they work can help you get
                    the most out of posing and animating with inverse kinematics.
                    The end of the IK handle, which is located at the end joint by default, is
                    called the end effector. The reason the end of the IK handle is called the “end
                    effector” is because it helps to bring about how the IK handle rotates the
                    joints in the joint chain so that the end of the chain can reach some location
                    in space. By telling the IK handle’s IK solver where the end of the IK handle
                    is, the end effector provides information the IK solver needs to figure out
                    how to rotate all the joints for you.




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             When you are posing and animating an IK chain, you also need to tell the IK
             solver the position and orientation in space where you would like the end
             effector to move to next. That information is provided by the IK handle’s
             goal. When you interactively pose an IK chain, what you are really doing is
             moving the IK handle’s goal. The IK solver looks at where the goal is, looks
             at where the end effector is, and figures out how to rotate all the joints in the
             IK chain to get the end effector to be where the goal is.
             A skeleton can have as many IK handles as you think you need for posing
             and animating its joint chains. However, be sure you are happy with which
             joint is the skeleton’s root joint before you begin creating IK handles. The
             skeleton’s root must not be between an IK chain’s start joint and end joint.
             You cannot create an IK chain that includes the root joint unless that joint is
             the start joint. Also, if you change which joint is the root joint, you will




                                                                                                 Animation
                                                                                                 Character
             invalidate IK chains that include the new root joint unless the joint is the
             start joint of an IK chain.

IK solvers
             IK solvers provide the motor intelligence of IK handles. IK solvers figure out
             how to rotate all the joints in a joint chain controlled by an IK handle. Maya
             offers four types of solvers:
         •   Single chain (SC) solver
         •   Rotate plane (RP) solver
         •   Spline solver
         •   Multi-chain (MC) solver

Single chain (SC) solver
             The single chain (SC) solver is ideal for posing and animating the IK chains
             for a character’s limbs, such as arms and legs. The single chain solver
             provides a straightforward mechanism for posing and animating a chain
             anywhere the joint chain can reach in the scene’s world space. The joint
             chain will tend to stay within the plane that best includes all the joint chain’s
             joints.
             An IK handle using a single chain is displayed as follows:




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                                                     Handle
                                                     vector

                        Start joint                             End joint          Goal




                                      Handle wire

                                                                            End effector



                     IK handle using single chain solver

                     Start joint
                    The start joint is where the IK handle begins. The start joint is the first joint
                    in the joint chain that is influenced by the IK handle. The start joint could be
                    the skeleton’s root joint or any other joint in the skeleton’s action hierarchy
                    above the end joint.

                     End joint
                    The end joint is the last joint in the joint chain controlled by the IK handle.
                    The end joint must be below the start joint in the skeleton’s action hierarchy.

                     Handle wire
                    The handle wire is the line that runs through all the joints and bones in a
                    joint chain controlled by the IK handle.The handle wire begins at the start
                    joint’s local axis and by default ends at the end joint’s local axis.

                     End effector
                    The end effector is the end of the IK handle. By default, the end effector is
                    located at the end joint’s local axis. However, the end effector can be offset
                    from the end joint. The end effector does not move from its location at the
                    end joint (or at some offset from the end joint) during posing and animating.
                    Also, note that the end effector is parented to the parent joint of the end
                    joint, not to the end joint.



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            Goal
            The goal indicates where you want an IK handle’s end effector to be. The
            goal, which is indicated by an axis, rests at the IK handle’s end effector.
            During posing, you can move the goal to any location in the scene’s world
            space. The IK handle’s end effector tries to keep up with the goal at all times.
            The IK handle’s single chain (SC) solver figures out how the end effector can
            have the same position and orientation as the goal’s position and orientation.
            The single chain (SC) solver figures out how to rotate the joint chain’s joints
            so that the end effector can reach the goal. However, depending on the
            rotational limits and fully extended length of the joint chain, the end effector
            might not be able to reach the goal’s current position and orientation.

            Handle vector




                                                                                               Animation
                                                                                               Character
            The handle vector is the line drawn from the start joint to the IK handle’s
            end effector. The end effector is normally located at the IK chain’s end joint.
            The purpose of the handle vector is to indicate at which joints the IK handle
            starts and ends. Because of the handle vector’s similarity to what some
            systems call a limb axis, some expert users refer to the handle vector as the
            limb axis.

            Single chain solver behavior
            The single chain solver first looks at the position (the translate X, Y, and Z
            attributes) and orientation (the rotate X, Y, and Z attributes) of the goal.
            Next, the solver figures out how to move the position and orientation of the
            end effector as close to the goal’s position and orientation as possible. To do
            that, the solver figures out how to best rotate the joints in the IK handle’s
            joint chain.
            Expert users have found that single chain solver IK chains that consist of
            between two and four joints are the easiest to pose. Extremely long IK chains
            can become awkward to pose and animate.
            Note that the joint chain controlled by an IK handle using a single chain
            solver cannot have any other IK handles running through any of its joints.

Rotate plane (RP) solver
            Like the single chain (SC) solver, the rotate plane (RP) solver is ideal for
            posing IK chains for a character’s limbs such as arms and legs. However, the
            rotate plane solver offers more manipulator tools for posing the chain than
            does the single chain solver. Also, the rotate plane solver is ideal for IK


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                    chains that you would like to stay in more or less the same plane, even
                    though that plane can rotate. For example, the shoulder, elbow, and wrist
                    joints of an arm all stay within the same plane, but that plane rotates as the
                    shoulder joint rotates.
                    An IK handle using a rotate plane solver is displayed as follows:




                       Pole vector                                        Twist disc
                       axis

                                         Plane
                                         indicator                                        Goal
                                                          Handle vector


                       Pole vector
                                                                     Handle wire
                                                                                       End joint
                           Rotate disc
                                            Start joint

                     IK handle using rotate plane solver

                     Start joint
                    The start joint is where the IK handle begins. The start joint is the first joint
                    in the joint chain that is influenced by the IK handle.The start joint could be
                    the skeleton’s root joint, or any other joint in the skeleton’s action hierarchy
                    above the end joint.

                     End joint
                    The end joint is the last joint in the joint chain controlled by the IK
                    handle.The end joint must be below the start joint in the skeleton’s action
                    hierarchy.

                     Handle wire
                    The handle wire is the line that runs through all the joints and bones in a
                    joint chain controlled by the IK handle. The handle wire begins at the start
                    joint’s local axis and by default ends at the end joint’s local axis.


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End effector
The end effector is the end of the IK handle. By default, the end effector is
located at the end joint’s local axis. However, the end effector can be offset
from the end joint. The end effector does not move from its location at the
end joint (or at some offset from the end joint) during posing and animating.
Also, note that the end effector is parented to the parent joint of the end
joint, not to the end joint. You can use the Hypergraph to view the
relationships between the end effector and the joints in the joint chain.

Goal
The goal indicates where you want an IK handle’s end effector to be. The
goal, which is indicated by an axis, rests at the IK handle’s end effector.




                                                                                    Animation
                                                                                    Character
During posing, you can move the goal to any location in the scene’s world
space. The IK handle’s end effector tries to keep up with the goal at all times.
The IK handle’s rotate plane (RP) solver figures out how the end effector can
have the same position as the goal’s position. The rotate plane (RP) solver
figures out how to rotate the joint chain’s joints so that the end effector can
reach the goal. However, depending on the rotational limits and fully
extended length of the joint chain, the end effector might not be able to reach
the goal’s current location.

Handle vector
The handle vector is the line drawn from the start joint to the IK handle’s
end effector. The end effector is normally located at the IK chain’s end joint.
Because of the handle vector’s similarity to what some systems call a limb
axis, some expert users refer to the handle vector as the limb axis.

Joint chain plane
The joint chain plane is the plane that would best contain all the joints in the
joint chain. By always containing the joints in the joint chain, the joint chain
plane controls how the joint chain can twist. The joint chain plane is not
displayed because you can infer it from where the joint chain’s joints are
located. However, the joint chain plane’s orientation is indicated by the
plane indicator displayed in the rotation disc. The joint chain plane can
rotate about the handle vector. Rotating the joint chain plane about the
handle vector has the effect of twisting the joint chain. (The degree of twist is
measured relative to the reference plane, which is the plane defined by the
handle vector and the pole vector.)




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                     Rotation disc
                    The rotation disc is located at the start joint. The rotation disc indicates how
                    the joint chain plane can rotate, which twists the joint chain. An indicator in
                    the rotation disc, called the plane indicator, shows the orientation of the joint
                    chain plane.

                     Twist disc
                    The twist disc is located at the end joint. You can use the twist disc as a tool
                    to twist the joint chain by rotating the joint chain plane.

                     Plane indicator
                    The plane indicator indicates the orientation of the joint chain plane, which
                    is the degree of twist in the joint chain relative to the reference plane. The
                    plane indicator can be thought of as the reflection of the joint chain plane in
                    the rotation disc.

                     Reference plane
                    For the joint chain plane to rotate and twist the joint chain, the plane must
                    rotate relative to some other plane so that the degree of twist can be
                    measured. The plane that the joint chain plane rotates relative to is the
                    reference plane. The difference between the two planes indicates the amount
                    the joint chain twists. The reference plane is defined by the handle vector
                    and the pole vector.

                     Pole vector
                    Like the handle vector, the pole vector starts at the start joint. Unlike the
                    handle vector, which always ends at its IK handle’s end effector, the pole
                    vector can end anywhere you want it to end. The purpose of the pole vector
                    is to help define the reference plane. During posing, you can sometimes
                    move the end effector through the reference plane, which moves the handle
                    vector through the reference plane. When that happens, the handle vector
                    and pole vector can appear to cross as the joint chain suddenly flips because
                    the degree of twist suddenly changes by 180 degrees. Because the reference
                    plane is defined by the handle vector and the pole vector, you can prevent
                    the flipping effect by simply moving the end of the pole vector to redefine
                    the reference plane.




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            Rotate plane solver behavior
            The rotate plane solver first looks at the position (the translate x, y, and z
            attributes) of the goal. Next, the solver figures out how to move the position
            of the end effector as close to the goal’s position as possible. To do that, the
            solver figures out how to best rotate the joints in the IK handle’s joint chain.
            Unlike the single chain solver, the rotate plane solver does not look at the
            orientation (the rotate x, y, and z attributes) of the goal. That is, the rotate
            plane solver figures out how to rotate the joints based on the goal’s position,
            but not on the goal’s orientation. The orientation of the entire joint chain can
            be controlled by twisting the joint chain with the twist disc. However, unlike
            the single chain solver, you cannot rotate the joint chain by rotating the IK
            handle’s goal.




                                                                                                 Animation
                                                                                                 Character
            Expert users have found that rotate plane solver IK chains that consist of
            between two and four joints are the easiest to pose. Extremely long IK chains
            can become awkward to pose and animate.
            Note that the joint chain controlled by an IK handle using a rotate plane
            solver cannot have any other IK handles running through any of its joints.

Spline solver
            The IK spline solver lets you manipulate a long, flexible joint chain that
            conforms to the shape of a curve. This solver is useful for animating the
            motion of tails, spines, tentacles, snakes, long necks, and similar objects.
            Expert users have found that spline solver IK chains that include ten or more
            joints with relatively short bones are ideal.
            For information on using IK handles with the spline solver, please see
            “Using IK spline handles” on page 259.

Multi-chain (MC) solver
            The multi-chain (MC) solver is ideal for IK chains that can be posed and
            animated by more than one IK handle. In such a case, each IK handle should
            use the multi-chain solver.
            For information on using the multi-chain (MC) solver, please see “Activating
            the multi-chain (MC) solver” on page 243.




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Creating IK handles


Creating IK handles
                  IK handles are tools that help you pose and animate joint chains with inverse
                  kinematics. You can create an IK handle for almost any joint chain. A joint
                  chain that has an IK handle is called an IK chain.
                  In any IK chain, the joint where the IK handle starts should be closer to the
                  skeleton’s root joint than the joint where the IK handle ends. Also, an IK
                  chain should not include the root joint unless the root joint is the start joint.
                  You use the IK Handle Tool to create IK handles. You can set certain IK
                  Handle attributes during IK handle creation from the IK Handle Tool’s Tool
                  Settings window. After you create the IK handles, you can edit IK handle
                  attributes by using the Attributes Editor. Note that you can also use Maya
                  Embedded Language (MEL) commands to create and edit IK handles. Some
                  expert users like to define hotkeys based on MEL commands for quickly
                  creating customized joint chains and IK handles.
                  During inverse kinematics posing and animating, the rotations of all the
                  joints in the IK chain are calculated, or “solved,” by an IK solver. Note that
                  IK handles using the single chain (SC), rotate plane (RP), and spline solvers
                  require that the joint chains they control be solved only by them. For
                  example, two IK handles using one of the single chain (SC), rotate plane
                  (RP), or spline solvers cannot overlap, allowing both to solve some of the
                  same joints.
                  Expert users have found that IK chains that consist of between two and four
                  joints are the easiest to pose and animate. Extremely long IK chains can
                  become awkward.
                  In creating IK handles, you can add IK handles to existing joint chains, or
                  you can create IK chains (joint chains with IK handles).

Adding an IK handle
                  You can create an IK handle for any joint chain.

                  To create an IK handle:
              1   Select Skeletons→IK Handle Tool.
              2   To change the tool options, select Skeletons→IK Handle Tool-Ë to open the
                  IK Handle Tool Options window.
                  See “Editing IK handle attributes” on page 246 for a description of the IK
                  Handle Tool options.


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         3   With the left mouse button, click the start joint and end joint for the IK
             handle.
             You can click the joints in either order: the IK handle is created with the end
             effector on the child joint.

Creating an IK chain
             An IK chain is a joint chain that has an IK handle. You can create IK chains
             in the same way that you create joint chains, but you must set the Joint
             Tool’s Create IK Handle option.

             To create an IK chain:




                                                                                                  Animation
                                                                                                  Character
         1   Select Skeletons→Joint Tool-Ë to open the Joint Tool’s Tool Settings
             window.
         2   Toggle on the Create IK Handle option.
             You can set IK handle options within the IK Handle Options heading. Click
             the triangle on the heading line to view the options. For information on IK
             Handle options, see “Editing IK handle attributes” on page 246.
         3   Create the joint chain as you would any skeleton. First, Click in the
             workspace at the position of the first joint.
             The joint is created.
         4   Move the pointer to the position you want the second joint to be and click
             again.
             The two joints are connected with a bone that indicates the direction of the
             joint chain’s hierarchy: the thinner end of the bone’s triangle points to the
             child joint.
             See “Positioning joints” on page 196 for tips on editing the positions of
             joints.
         5   Continue moving the pointer and clicking until you have created the chain
             of joints for the skeleton.
         6   When you finish creating all joints in the chain, press the Enter key.
             Ending the joint chain creates the IK handle.
             You can edit the IK handle in the Attribute Editor to change its attributes.




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Displaying IK handle’s end effector
                  A marker that identifies an IK handle’s end effector is not displayed by
                  default when you create an IK handle. However, if you would like to see the
                  end effector, you can tell Maya to display it.

                  To display end effector:
              1   Choose Window→Hypergraph to open the Hypergraph.
              2   In the Hypergraph, select the IK handle’s end effector.
              3   With the end effector selected, continue to press the right mouse button, and
                  from the pull-down menu, select Show.
                  An axis-shaped icon indicates the end effector.

Displaying IK handle’s goal and goal’s axis
                  Markers that identify an IK handle’s goal and the local axis of the goal are
                  not displayed by default when you create an IK handle. However, you can
                  tell Maya to display them after you create the IK handle.

                  To display goal and goal’s axis:
              1   Select the IK handle.
              2   Choose Window→Attribute Editor to open the Attribute Editor.
              3   Open Display if not opened.
              4   In Display, click Display Handle on to display the IK handle’s goal.
              5   In Display, click Display Local Axis to display the axis of the IK handle’s
                  goal.

Displaying IK handle’s twist disc and pole vector’s axis
                  An IK handle using the default rotate plane (RP) solver has two
                  manipulators that are not displayed by default when you create an IK
                  handle. These manipulators are the twist disc and the pole vector’s axis.

                  To display twist disc and pole vector’s axis:
              1   Select the IK handle.
              2   Click the Show Manipulator Tool icon.



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             If the IK handle uses the default rotate plane (RP) solver, the twist disc is
             displayed at the IK chain’s end joint. Also, the pole vector’s axis is displayed.
             If the IK handle uses the single chain (SC) solver, no additional manipulators
             are displayed.


Setting IK handle creation options
             You can have the various options and attributes of IK handles set
             automatically when you create the IK handle, or you can edit the IK handle’s
             attributes at any time. This section describes how to set IK handle creation
             options. To edit attributes after you create an IK handle chain, see “Editing
             IK handle attributes” on page 246.




                                                                                                 Animation
                                                                                                 Character
             Setting automatic IK handle attributes includes:
         •   “Viewing IK handle creation options” on page 241
         •   “Setting the current solver” on page 242
         •   “Setting autopriority” on page 243
         •   “Setting solver enable” on page 244
         •   “Setting snap enable” on page 244
         •   “Setting sticky” on page 244
         •   “Setting priority” on page 245
         •   “Setting weight” on page 245
         •   “Setting position vs. orientation (PO) weight” on page 246

Viewing IK handle creation options
             The IK handle creation options can be set from the IK Handle Tool’s Tool
             Settings window. When you create an IK handle, you use the IK Handle
             Tool. You can set the IK Handle Tool’s settings so that certain IK handle
             attributes will be set automatically.




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                   The IK Handle Tool’s Tool Settings window

                   To view automatically set IK handle attributes:
                   Select Skeletons→IK Handle Tool-Ë.
                   The IK Handle Tool’s Tool Settings window is displayed.

Setting the current solver
                   You can have either the single chain solver or the rotate plane solver set as
                   the current solver automatically provided when you create an IK handle.

                   To set the current solver:
               1   Select Skeletons→IK Handle Tool-Ë.


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          2   From the Current Solver pop-up menu, select either ikRPsolver or
              ikSCsolver.
              The rotate plane (RP) solver (called the ikRPsolver) is the default solver. The
              other solver you can select here is the single chain solver (called the
              ikSCsolver). Depending on the plug-ins you are using, other solvers may be
              available.
              To use the spline solver, you must work directly with the IK Spline Handle
              Tool (Skeletons→IK Spline Handle Tool).
              You can select the multi-chain (MC) solver if it has already been activated.

Activating the multi-chain (MC) solver




                                                                                                   Animation
                                                                                                   Character
              The multi-chain (MC) solver is only available through the use of a Maya
              Embedded Language (MEL) command. Once you enter the command, you
              can choose the multi-chain solver from the IK Handle Tool’s Tool Settings
              window.

              To activate the multi-chain solver:
          1   Choose Window→General Editors→Command Shell...
          2   In the Command Shell, enter the following command at the mel: prompt:
              createNode ikMCsolver.

              Now you can choose the multi-chain (MC) solver in the IK Handle Tool’s
              Tool Settings window.

Setting autopriority
              You can control the order in which IK chains are solved by having Maya
              automatically set their priority based on where the start joints are in the
              skeleton’s action hierarchy. When Maya automatically sets priority, IK
              chains whose start joint is the skeleton’s root joint have a priority of 1. IK
              chains whose start joints are child joints of the root joint have a priority of 2,
              and so on down the skeleton’s action hierarchy. The further an IK chain’s
              start joint is from the root joint, the lower its priority.

              To set autopriority:
          1   Select Skeletons→IK Handle Tool-Ë.
          2   Click Autopriority on or off. If off, all IK handles are given a priority of 1.



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Setting solver enable
                   After you create an IK handle for a joint chain, you can immediately begin
                   posing the new IK chain with inverse kinematics. However, if you would
                   like to pose with forward kinematics, you can temporarily turn off the IK
                   handle’s IK solver.

                   To set solver enable:
               1   Select Skeletons→IK Handle Tool-Ë.
               2   Click Solver Enable off or on (the default is on).

Setting snap enable
                   During posing, an IK handle’s goal can exceed the reach of the IK chain.
                   Maya will show you this by continuing to draw a line between the end
                   effector, which is located at the IK chain’s end joint by default, and the goal.
                   When you release the mouse button, the goal will snap back to the IK
                   handle’s end effector by default. If you prefer, you can have the goal remain
                   wherever you have moved it last, rather than have it snap back to the end
                   effector. Whether the goal snaps back or remains in its last location is largely
                   a matter of personal preference. At times some expert users like to see where
                   the goal is after it has exceeded the reach of the IK chain so they can make
                   adjustments more easily to the overall position of the entire skeleton.

                   To set snap enable:
               1   Select Skeletons→IK Handle Tool-Ë.
               2   Click Snap Enable off or on (the default is on).

Setting sticky
                   You can have an IK handle’s goal stick to any location in the scene. When
                   you move the start joint of the IK chain, or even the entire skeleton, the end
                   joint of the IK chain with a sticky IK handle will stick to its location while the
                   IK solver provides the appropriate joint rotations. For example, if you are
                   animating a human character that is reaching up or out while standing in
                   place, you can animate the natural articulation of the legs much more easily
                   by making the IK handles that end at the character’s feet sticky.

                   To set sticky:
               1   Select Skeletons→IK Handle Tool-Ë.

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          2   Click Sticky on or off.

Setting priority
              You can control the order in which a skeleton’s various IK handles calculate
              joint chain action during animation. Each IK handle can be assigned a
              priority. IK handles with a priority of 1 will be solved first, IK handles with a
              priority of 2 will be solved second, and so on.
              Maya can set these priorities for you based on where an IK handle’s start
              joint is in a skeleton’s action hierarchy, or you can give all IK handles a
              priority of 1. Having varied priorities for IK handles can improve overall
              inverse kinematics performance.




                                                                                                  Animation
                                                                                                  Character
              To set priority:
          1   Select Skeletons→IK Handle Tool-Ë.
          2   Slide Priority value to desired setting. Highest priority is 1.

Setting weight
              During animation, a skeleton with many IK chains can perform a wide
              variety of motions. Because of the specific ways the motions of IK chains can
              affect the overall position and orientation of the character’s skeleton, not all
              the end effectors may be able to reach their goals simulaneously.
              Consequently, some of the interpolated IK chain motions might not provide
              the effects you wish. For example, on a given limb with two IK chains that
              have the same priority, neither of the two IK chains might be able to reach
              their goals because they are pulling the limb in different directions. You can
              alleviate this situation by assigning the IK handles of those IK chains a
              weight.
              The assigned weight, combined with the current distance between an IK
              handle’s end effector and its goal, serve to prioritize the solutions of IK
              chains whose IK handles have the same priority settings.
              When the end effectors of two or more IK handles with the same priority
              cannot reach their goals simultaneously, the IK handles whose end effectors
              are furthest from their goals and whose weights are greatest will be solved
              first.

              To set weight:
          1   Select Skeletons→IK Handle Tool-Ë.


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              2   Slide Weight value to desired setting (must be 0 or greater).

Setting position vs. orientation (PO) weight
                  During animation, an IK handle’s end effector might be able to reach the
                  goal’s position or the goal’s orientation, but not both. You can control the
                  extent to which the end effector can reach the goal’s position versus the
                  goal’s orientation by setting the position vs. orientation (PO) weight. The
                  value of the PO weight ranges between 0 and 1. With a PO weight of 1, the
                  end effector will seek to reach only the goal’s position. With a PO weight of
                  0, the end effector will seek to reach only the goal’s orientation. With a PO
                  weight of 0.7, the end effector will seek to reach the goal’s position more
                  than the orientation. Finally, with a PO weight of 0.5, the end effector will
                  try to reach the goal’s position and orientation as equally as possible.
                  Note that IK handles using the rotate plane (RP) solver do not consider the
                  orientation of the goals, only the position. With IK chains being solved by
                  the RP solver, you control IK chain orientation by means of the twist disc.

                  To set position vs. orientation (PO) weight:
              1   Select Skeletons→IK Handle Tool-Ë.
              2   Slide POWeight value to desired setting.


Editing IK handle attributes
                  You can edit the attributes of an IK handle at any time by using the Attribute
                  Editor. This section describes how to use the Attribute Editor to edit an IK
                  handle’s attributes.
                  Editing IK handle attributes includes:
              •   “Viewing editable IK handle attributes” on page 247
              •   “Renaming an IK handle” on page 249
              •   “Editing transform attributes” on page 249
              •   “Editing skeleton info” on page 250
              •   “Editing IK handle attributes” on page 250
              •   “Editing IK solver attributes and choosing an IK solver” on page 251
              •   “Editing pivots” on page 251
              •   “Editing limit information” on page 252

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         •   “Editing display” on page 252
         •   “Editing node behavior” on page 253
             Note that you can access settings for an IK handle’s attributes, and also the
             Attribute Editor, by pressing the right mouse button while the cursor is on
             the IK handle you want to edit.

Viewing editable IK handle attributes
             To view or edit an IK handle’s attributes, use the Attribute Editor.




                                                                                               Animation
                                                                                               Character




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                  Attribute Editor for IK handles


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             To view editable joint attributes:
             Choose Window→Attribute Editor to open the Attribute Editor.
             The Attribute Editor is displayed.

Renaming an IK handle
             Maya names IK handles for you when you create them. By default, IK
             handles are numbered consecutively as you create them. For example, the
             first handle would be called “ikHandle1,” the second “ikHandle2,” and so
             on. You can rename the IK handles to better reflect their purpose in posing
             and animating your character. It’s a good idea to give IK handles meaningful
             names so that they are easier to select when you are working with Maya’s




                                                                                               Animation
                                                                                               Character
             editors, using the Hypergraph, or using the Outliner. For example, you
             could name an IK handle that goes from a right shoulder joint to a right
             wrist joint “RShtoWrist.”

             To rename an IK handle:
         1   Select the IK handle.
         2   Choose Window→Attribute Editor to open the Attribute Editor.
         3   Enter the new name in the ikHandle: field.
             The new name takes effect immediately.

Editing transform attributes
             An IK handle’s transform attributes include the following:
         •   Translate, rotate, scale, and shear transformations
         •   Rotate order
         •   Rotate axis
         •   Inherits transform option

             To edit transform attributes:
         1   Select the IK handle.
         2   Choose Window→Attribute Editor to open the Attribute Editor.
         3   Open Transform Attributes if not opened.




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              4   In Transform Attributes, you can make changes to the translate, rotate, scale,
                  and shear transformations. You can set the rotate order, which is by default
                  set to xyz. You can change the location of the rotate axis, which is by default
                  set to 0.0, 0.0, 0.0. Finally, you can toggle whether or not the IK handle
                  inherits transformations.

Editing skeleton info
                  An IK handle’s skeleton info include the following:
              •   Start joint
              •   End effector

                  To edit skeleton info:
              1   Select the IK handle.
              2   Choose Window→Attribute Editor to open the Attribute Editor.
              3   Open Skeleton Info if not opened.
              4   In Skeleton Info, note that the names of the IK handle’s start joint and end
                  effector are displayed. You can edit either of these by clicking on the right
                  arrow buttons next to their names.

Editing IK handle attributes
                  An IK handle’s handle attributes include the following:
              •   Snap enable
              •   Stickiness
              •   Priority
              •   Weight
              •   Position vs. orientation (PO) weight

                  To edit IK handle attributes:
              1   Select the IK handle.
              2   Choose Window→Attribute Editor to open the Attribute Editor.
              3   Open IK Handle Attributes if not opened.
              4   In IK Handle Attributes, you can edit snap enable, stickiness, priority,
                  weight, and position vs. orientation (PO) weight.


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                                                                 Editing IK handle attributes


Editing IK solver attributes and choosing an IK solver
             An IK handle’s solver attributes include the following:
         •   Solver enable
         •   IK solver selection (single chain solver, rotate plane solver, or the multi-
             chain solver if activated)
         •   Pole vector’s end location
         •   Twist

             To edit solver attributes and choose IK solver:
         1   Select the IK handle.




                                                                                                  Animation
                                                                                                  Character
         2   Choose Window→Attribute Editor to open the Attribute Editor.
         3   Open IK Solver Attributes if not opened.
             In IK Solver Attributes, you can choose the IK solver, snap enable, stickiness,
             priority, weight, and position vs. orientation (PO) weight.
         4   In IK solver, choose the IK solver you want to assign to the IK handle.
             By default, only two IK solvers are offered here: the single chain solver
             (ikSCsolver) and the rotate plane solver (ikRPsolver), which is the default IK
             solver.
             To use the spline solver, you must work directly with the IK Spline Handle
             Tool (Skeletons→IK Spline Handle Tool).

Editing pivots
             An IK handle’s pivots attributes include the following:
         •   Display rotate pivot toggle
         •   Display scale pivot toggle
         •   Local space rotate pivot and scale pivot
         •   World space rotate pivot and scale pivot

             To edit pivots attributes:
         1   Select the IK handle.
         2   Choose Window→Attribute Editor to open the Attribute Editor.
         3   Open Pivots if not opened.


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              4   In Pivots, you can edit the display rotate pivot toggle and the display scale
                  pivot toggle. Also, you can edit the coordinates for the local space pivot’s
                  rotate and scale transformations and the world space pivot’s rotate and scale
                  transformations.

Editing limit information
                  An IK handle’s limit information attributes include the following:
              •   Translation transformation limits
              •   Rotation transformation limits
              •   Scale transformation limits

                  To edit limit information attributes:
              1   Select the IK handle.
              2   Choose Window→Attribute Editor to open the Attribute Editor.
              3   Open Limit Information if not opened. Below it you can open Translate,
                  Rotate, and Scale.
              4   In Translate, Rotate, or Scale, edit the minimum, current, and maximum
                  transformation limits.

Editing display
                  An IK handle’s display attributes include the following:
              •   Display handle
              •   Display local axis
              •   Select handle
              •   Show manipulator default
              •   Visibility
              •   Template

                  To edit display attributes:
              1   Select the IK handle.
              2   Choose Window→Attribute Editor to open the Attribute Editor.
              3   Open Display if not opened.



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          4   In Display, toggle the Display Handle and Display Local Axis settings. Edit
              the coordinates of the Select Handle location. Select Show Manip Default as
              None, Translate, Rotate, or Scale. Check Visibility on or off, and check
              Template on or off.

Editing node behavior
              Maya’s system thinks of all its entities, including IK handles, as nodes. An IK
              handle’s node behavior attributes include the following:
          •   Caching
          •   Node state




                                                                                                Animation
                                                                                                Character
              To edit node behavior attributes:
          1   Select the IK handle.
          2   Choose Window→Attribute Editor to open the Attribute Editor.
          3   Open Node Behavior if not opened.
          4   In Node Behavior, check Caching on or off. Select Node State as Normal,
              HasNoEffect, or Blocking.


Editing IK solvers
              You can edit the settings of the IK solvers from the Attribute Editor. By
              default, Maya names the single chain solver the “ikSCsolver” and the rotate
              plane solver the “ikRPsolver.” Editing IK solver settings includes:
          •   Editing IK solver attributes: maximum iterations and tolerance
          •   Editing node behavior

Editing IK solver attributes
              An IK solver’s attributes include the following:
          •   Maximum iterations
          •   Tolerance

              To edit solver attributes:
          1   Select the IK solver.
          2   Choose Window→Attribute Editor to open the Attribute Editor.

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              3   Open IK Solver Attributes if not opened.
              4   In IK Solver Attributes, edit the Max Iterations setting and the Tolerance
                  setting.

Editing node behavior
                  Maya’s system thinks of all its entities, including IK solvers, as nodes. An IK
                  solver’s node behavior attributes include the following:
              •   Caching
              •   Node state

                  To edit node behavior attributes:
              1   Select the IK solver.
              2   Choose Window→Attribute Editor to open the Attribute Editor.
              3   Open Node Behavior if not opened.
              4   In Node Behavior, check Caching on or off. Select Node State as Normal,
                  HasNoEffect, or Blocking.


Using IK systems
                  An IK system can organize and manage a collection of IK solvers.

Creating an IK system
                  To create an IK system:
              1   Choose Window→Attribute Editor to open the Attribute Editor.
              2   Choose List→Auto Update, clicking auto update off (not checked).
              3   Choose List→Kinematics→IK Systems.
              4   Choose Object→ikSystem.
                  The Attribute Editor will now show information about an IK system whose
                  default name is “ikSystem.” You can change the name by typing in a new
                  name in the ikSystem: field.




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Accessing an IK system
             To access an IK system:
         1   Select an IK handle.
         2   Choose Window→Attribute Editor to open the Attribute Editor.
         3   In the Attribute Editor, click on Set Focus.
             The Attribute Editor will now display information about the IK system.

Renaming an IK system
             You can rename an IK system.




                                                                                                Animation
                                                                                                Character
             To rename an IK system:
         1   Access the IK system with the Attribute Editor.
         2   In the ikSystem: field, replace the current name with the name you would
             like to use.

Viewing an IK system’s IK solvers
             You can view and select the IK solvers Maya provides from the IK system.

             To view available IK solvers:
         1   Access the IK system with the Attribute Editor.
         2   Open ikSystem if not opened.
             The available IK are listed. By default, three IK solvers are listed: the single
             chain (SC) solver (default name: ikSCsolver), the rotate plane solver (default
             name ikRPsolver), and the spline solver (default name: ikSplineSolver).
             You can select and edit the solvers by double-clicking on the names in the
             list. When you double-click, Maya creates folders for the selected solvers in
             the Attribute Editor.

Editing global snap and global solve
             You can edit the global snap and global solve settings.

             To edit global snap and solve settings:
         1   Access the IK system with the Attribute Editor.

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              2   Open ikSystem if not opened.
                  Note the Global Snap and Global Solve check boxes below the listing of
                  available IK solvers.
              3   Click the Global Snap and Global Solve settings on or off.

Editing node behavior
                  Maya’s system thinks of all its entities, including IK systems, as nodes.The
                  IK system’s node behavior attributes include the following:
              •   Caching
              •   Node State

                  To edit node behavior attributes:
              1   Select the IK solver.
              2   Choose Window→Attribute Editor to open the Attribute Editor.
              3   Open Node Behavior if not opened.
              4   In Node Behavior, check Caching on or off. Select Node State as Normal,
                  HasNoEffect, or Blocking.


Posing IK chains
                  Posing IK chains includes the following:
              •   Posing with single chain (SC) solver IK handles
              •   Positioning with rotate plane (RP) solver IK handles
              •   Twisting with rotate plane (RP) solver IK handles
              •   Eliminating flip in rotate plane (RP) solver IK handles
              •   Sticky posing

Posing with single chain (SC) solver IK handles
                  To pose single chain (SC) solver IK handles:
              1   Select the IK handle.




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              You can select the IK handle directly or from the Hypergraph. In the
              Hypergraph, note that next to each end effector there is an icon you can click
              on to select the IK handle that the end effector belongs to.
          2   Select the Move Tool or the Rotate Tool.
          3   Press the right mouse button and pose the IK handle.
          4   The joint chain will move or rotate as you move the mouse.

Positioning with rotate plane (RP) solver IK handles
              To position rotate plane (RP) solver IK handles:
          1   Select the IK handle.




                                                                                                  Animation
                                                                                                  Character
              You can select the IK handle directly or from the Hypergraph. In the
              Hypergraph, next to each end effector is an icon you can click on to select
              the IK handle that the end effector belongs to.
          2   Select the Move Tool.
          3   Press the right mouse button and position the IK handle.
              The joint chain will move as you move the mouse.

Twisting with rotate plane (RP) solver IK handles
              To twist a joint chain with a rotate plane (RP) solver IK handle:
          1   Select the IK handle.
              You can select the IK handle directly or from the Hypergraph. In the
              Hypergraph, next to each end effector is an icon you can click on to select
              the IK handle that the end effector belongs to.
          2   Select the Show Manipulator Tool.
          3   Click on the twist disc (located at the end joint of the joint chain). With the
              right mouse button pressed, move the mouse to twist the joint chain.

Eliminating flip in rotate plane (RP) solver IK handles
              To eliminate flip:
          1   Select the IK handle if not already selected.




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                  You can select the IK handle directly or from the Hypergraph. In the
                  Hypergraph, next to each end effector is an icon you can click on to select
                  the IK handle that the end effector belongs to.
              2   Select the Show Manipulator Tool.
              3   Select the pole vector.
                  Note that the triangular object in the rotation disc is not the pole vector. That
                  object is the plane indicator. The plane indicator indicates the orientation of
                  the joint chain plane.
              4   Drag the pole vector so that it will not cross the handle vector. Preventing
                  the handle vector from crossing the pole vector will eliminate flipping.
                  The joint chain might twist while you drag the pole vector. This is because
                  when you change the pole vector, you change the orientation of the
                  reference plane. The joint chain’s twist is defined in terms of the difference in
                  degrees between the reference plane and the joint chain plane.

Sticky posing
                  When you position a joint chain with IK handles, you might want to stick
                  one or more IK handles to a location in space while you move other IK
                  handles. This “sticking” feature of IK handles is useful for positioning
                  characters engaging in movement where some part of the skeleton is
                  stationary during part of the motion. For example, your character might be
                  interacting with a solid object such as a floor or a step on a stairway.
                  When you make an IK handle sticky, the IK handle sticks as if stuck by a
                  piece of gum. The IK handle tends to stay stuck, but can be pulled away
                  depending on how you are moving the skeleton. The IK handle’s goal and
                  end effector tend to stay together, but can sometimes separate. A sticky IK
                  handle is indicated by a dark red sphere on the IK handle’s goal.
                  Note that sticky IK handles are only for interactive placement of a skeleton
                  in a keyframe. They are not active when you play an animation.

                  To do sticky posing:
              1   Select the IK handle if not already selected.
              2   Choose Window→Attribute Editor to open the Attribute Editor.
              3   Open IK Handle Attributes if not opened.
              4   In IK Handle Attributes, set stickiness to sticky.



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                                                          Posing and Animating Skeletons
                                                                     Using IK spline handles


             The dark red sphere at the IK handle’s goal indicates that the IK handle is
             now sticky. The IK handle’s goal is now set to the goal’s current position and
             orientation for as long as the IK handle is sticky.
         5   Pose the skeleton as desired. The sticky IK handle tries to keep its joint chain
             always reaching for where you’ve stuck the IK handle’s goal.


Using IK spline handles
             You can add an IK spline handle to a joint chain to animate the motion of
             tails, necks, spines, tentacles, bullwhips, snakes, and similar objects. After
             you add the handle, Maya’s IK spline solver rotates the joints when you
             manipulate a curve that’s part of the handle.




                                                                                                    Animation
                                                                                                    Character
                                          The seven IK spline handles
                                          on this creature control its
                                          neck, back, tail, and flippers.




                                                Plesiosaur by Matt Dougan


Creating IK spline handles
             You add an IK spline handle to a joint chain. To animate the joint chain, you
             manipulate a curve that’s part of the handle. You don’t manipulate the
             translation of the handle. You can also roll or twist the joint chain with
             convenient manipulators.




                                                                 Using Maya: Animation        259
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Using IK spline handles


                  The joint chain can be an independent hierarchy or part of a larger hierarchy.
                  By default, a curve is created for you when you create an IK spline handle.
                  Instead, you can create your own curve before you create the handle. In
                  either case, the joint chain mimics the shape of the curve.

                  To create an IK spline handle with a default curve and options:
              1   Create a joint chain.
                  To ensure the joint chain moves smoothly when you animate the curve,
                  create many joints close to each other (with short bones).
              2   Select Skeletons→IK Spline Handle Tool.
              3   Select the start joint for the IK handle.
              4   Select the end joint for the IK handle.
                  The IK spline handle appears on the joint chain with an automatically
                  created curve. The joints in the chain rotate to adapt to the shape of the
                  curve.

                  To create an IK spline handle with your own curve and options:
              1   Use modeling tools to create the curve.
                  Create a simple curve with no sharp bends to ensure the joint chain moves
                  smoothly when you animate the curve.
                  If you create a curve with fewer CVs, your control of the curve’s shape and
                  skeleton’s movement will be less precise, but you’ll be able to manipulate
                  the curve and its joint chain easier. With fewer CVs, you spend less time
                  selecting and dragging CVs, and you’re more likely to have a smooth curve.
                  Start with a curve having as few CVs as necessary. Add CVs only as needed
                  to improve control.
              2   Create a joint chain.
                  To ensure the joint chain moves smoothly when you animate the curve,
                  create many joints close to each other (with short bones).
              3   Select Skeletons→IK Spline Handle Tool-Ë.
                  The Tool Settings window appears. Set options as described in “Setting
                  options before creating the IK spline handle” on page 265. Turn off Auto
                  Create Curve. The option settings are saved for future use.
              4   Select the start joint for the IK handle.


260   Using Maya: Animation
                                                         Posing and Animating Skeletons
                                                                    Using IK spline handles


         5   Select the end joint for the IK handle.
         6   Select the curve.
             The IK spline handle appears on the joint chain. The joints in the chain rotate
             to adapt to the shape of the curve. If the curve is shorter than the joint chain,
             the extra length of the joint chain points out from the end of the curve in a
             straight line.

Animating the joint chain
             To animate the joint chain, you set keys for the appropriate attributes after
             you do any of these actions:
         •   manipulate the CVs of the curve




                                                                                                 Animation
                                                                                                 Character
         •   twist and roll the joint chain
         •   slide the joint chain along the curve
         •   translate, rotate, and scale the curve
             To see the effects of animating the joint chain more clearly, bind skin to the
             joint chain.

             To manipulate the CVs of the curve:
         1   Select the curve.
             To select a curve without selecting joints or other objects in the workspace,
             turn on      (Select by object type) and limit the selection specifiers to
             NURBS Curves. See Using Maya: Basics for details. You can also select the
             curve conveniently in the Outliner or Hypergraph.
             It’s helpful to display CVs and hulls as you work with CVs. With the curve
             selected in Select by object type mode, turn on Display→NURBS
             Components→CVs and Hulls.
         2   Move the CVs.
             Turn on      (Select by component type) and use the Move tool on the CVs.
             or
             From the Modeling menu, select Curves→Curve Editing Tool.
         3   Select Keys→Set Key to set keys at the desired frames.




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                                                        Tip
                  To improve speed as you play and scrub your animation, set keys only for
                  the CVs you animate. For instance, select the CVs, then choose Keys→Set
                  Key.
                  If you use the Curve Editing Tool, select Keys→Set Key-Ì, turn on All
                  Manipulator Handles, and click the Save button. Thereafter when you
                  choose Set Key, Maya sets keys only for the necessary CVs.

                  To twist and roll the joint chain:
              1   Select the IK spline handle.
                  To select the handle in the workspace, drag a selection box around the end
                  joint. The default selection priority ensures you’ll select the handle rather
                  than the end joint.
              2   Select Modify→Transformation Tools→Show Manipulator Tool.
                  Circular manipulators appear at the start joint and end joint.



                                                              Twist manipulator



                   Start joint

                                                                         End joint



                         Roll manipulator




              3   To roll the entire joint chain, click and rotate the circular manipulator at the
                  start joint.
              4   To twist the joint chain, click and rotate the circular manipulator at the end
                  joint.




262   Using Maya: Animation
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                                                           Using IK spline handles


    You can also adjust twist and roll by selecting the IK handle and entering
    values for Roll and Twist in the Channel Box or Attribute Editor. In the
    Attribute Editor, expand the IK Solver Attributes section to see these
    attributes.
5   Set keys for the handle’s Roll and Twist attributes.
    If the IK handle’s Solver Enable is on, the solver doesn’t use the IK handle’s
    Translate, Rotate, and Scale values as it rotates joints.

    To slide the joint chain along the curve:
1   Select the IK handle.
    To select the IK handle, turn on      (Select by object type) then drag a




                                                                                       Animation
                                                                                       Character
    selection box around the end joint of the handle. The default selection
    priority ensures you’ll select the handle rather than the end joint.
2   Choose Window→Attribute Editor to display the Attribute Editor.
3   Expand the IK Solver Attributes section.
4   Turn on Root on Curve.
    This constrains the start joint of the IK spline handle to a position on the
    curve. It also provides an offset manipulator to slide the start joint along the
    curve.
5   Choose Modify→Transformation Tools→Show Manipulator Tool.
    The offset manipulator appears at the start joint.




                                                      Using Maya: Animation      263
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                         Offset manipulator
                         at the start joint


              6   Drag the manipulator to slide the joint chain along the curve.
                  If you drag the start joint to the end of the curve, the child joints move off
                  the end of the curve in a straight line.




                                                                Offset manipulator at
                                                                the end of the curve




                  You cannot drag the manipulator past either end of the curve.
                  You can also enter values for Offset in the Attribute Editor to move the start
                  joint’s offset manipulator along the curve. Try various values over 0 to get
                  the desired position.


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                                                                    Using IK spline handles


             The Offset attribute is ignored if you turn Root on Curve off.
         7   Set keys for the Offset at the desired frames.

                                                  Note
             If you use Offset (or the offset manipulator) to animate a joint chain sliding
             on a curve, the start joint might flip unexpectedly. Use Offset only for
             small movements or when the start joint doesn’t rotate much.
             You can also use a motion path to prevent joint flipping. See “Preventing
             unwanted start joint flipping” on page 272.

             To translate, rotate, and scale the curve:




                                                                                                Animation
                                                                                                Character
         1   Select the curve.
         2   Use the Move, Rotate, and Scale tools to translate, rotate, or scale the curve.
             If you created the handle with Root on Curve off, translating, rotating, and
             scaling the curve doesn’t translate the start joint.
         3   Set keys for the appropriate Translate, Rotate, and Scale attributes.

Setting options before creating the IK spline handle
             This topic describes how to set IK spline handle tool options available before
             you create the handle. See “Tips for working with IK spline handles” on
             page 274 for additional information on how to use several of these options.
             For details on options you can set after creation, see “Setting attributes after
             creating the IK spline handle” on page 271.

             To set IK Spline Handle Tool options:
             Select Skeletons→IK Spline Handle Tool-Ë
             Set the following options in the Tool Settings window.




                                                               Using Maya: Animation     265
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Using IK spline handles




                  Root on Curve
                  If you turn this option on, the start joint of the IK spline handle is
                  constrained to a position on the curve. You can drag an offset manipulator to
                  slide the start joint (and its children) along the curve.
                  If you turn this option off, you can move the start joint away from the curve.
                  The start joint is no longer constrained to the curve. Maya ignores the Offset
                  attribute, and no offset manipulator exists at the start joint.




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                                         You can move the start
                                         joint and its children off
                                         the curve by turning off




                                                                                    Animation
                                                                                    Character
                                         Root on Curve.




                                     Note
If Root on Curve is off, the solver ignores any motion you previously
keyed with Offset. Set keys with Root on Curve off or on, not a mixture of
both.

If Root on Curve is off and you move the start joint far enough away from
the curve so that none of the joints can reach the curve, the bones point
straight at the closest point on the curve. If the curve is wavy, the joints jump
from closest point to closest point as you move the straightened joint chain
towards parts of the curve. This is correct operation.
The following figure shows a joint chain in four positions as it points
towards the closest part of the curve.




                                                   Using Maya: Animation     267
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                  You can also turn Root on Curve on or off after you create the IK spline
                  handle by selecting the IK spline handle and displaying the Attribute Editor.
                  To display the Attribute Editor, select Window→Attribute Editor.

                  Auto Create Root Axis
                  This option creates a parent transform node above the start joint in the scene
                  hierarchy. You can avoid unexpected start joint flipping by moving and
                  rotating this transform node rather than the start joint. See “Preventing
                  unwanted start joint flipping” on page 272 for details.
                  You can turn this option on only when Root on Curve is off.
                  If you turn on Auto Create Root Axis, you must turn off Auto Parent Curve
                  if you want to use the curve as a motion path. Otherwise, a dependency
                  graph loop occurs, which results in the display of a warning message and
                  incorrect handle operation.
                  You can set Auto Create Root Axis in the Tool Options window only as you
                  create the IK spline handle.

                  Auto Parent Curve
                  If the start joint has a parent, this option makes the curve a child of that
                  parent. The curve and joints therefore move with the transformations of the
                  parent.
                  If you create a handle that starts at a joint in the chain lower than the root
                  joint of your skeleton, turn this option on so the joint chain moves with the
                  transformations of its parent joint.
                  You can set this option in the Tool Options window only as you create the
                  IK spline handle.

268   Using Maya: Animation
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                                                       Using IK spline handles


Snap Curve To Root
This option affects the handle only if you create your own curve for the
handle. If this option is on when you create the handle, the start of the curve
snaps to the position of the start joint. The joints in the chain rotate to adapt
to the shape of the curve.
If you want to move the joint chain to the curve to use the curve as a fixed
path, turn this option off. Otherwise, turn this option on.
You can set this option in the Tool Options window only as you create the
IK spline handle.

Auto Create Curve




                                                                                    Animation
                                                                                    Character
This option creates a curve used by the IK spline handle.
If you turn on Auto Create Curve and turn off Auto Simplify Curve, the
curve passes through all the joints. This often creates so many CVs that the
curve is unwieldy to manipulate. For this reason, consider turning on Auto
Simplify Curve.
If you turn on Auto Create Curve and Auto Simplify Curve, creating the
handle automatically creates a simplified curve that has a shape similar to
the joint chain. The higher the Number of Spans, the closer the curve
matches the joint chain. The curve has a curve degree of 3 (cubic).
If you turn off Auto Create Curve, you must supply a curve for the joint
chain.
If the joint chain is part of an existing skeleton, you’ll typically turn this
option on. If you’re using a curve as a path for sliding the joint chain, you’ll
typically turn this option off.
You can set Auto Create Curve in the Tool Options window only as you
create the IK spline handle.

Auto Simplify Curve
This option sets the automatically created curve to the specified Number of
Spans. The number of spans corresponds to the number of CVs in the curve.
The curve has a curve degree of 3 (cubic).
If you create a curve with fewer CVs, your control of the curve’s shape and
skeleton’s movement will be less precise, but you’ll be able to manipulate
the curve and its joint chain easier. With fewer CVs, you spend less time
selecting and dragging CVs, and you’re more likely to have a smooth curve.


                                                  Using Maya: Animation       269
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Using IK spline handles


                  This option works only if Auto Create Curve is on.
                  You can set Auto Simplify Curve in the Tool Options window only as you
                  create the IK spline handle.

                  Number of Spans
                  This option specifies the number of CVs in the curve as follows:


                   Number       CVs
                   of Spans

                   1            4

                   2            5

                   3            6

                   4            7

                  This option is available only if Auto Create Curve is on.
                  You can set the Number of Spans in the Tool Options window only as you
                  create the IK spline handle.

                  Root Twist Mode
                  This option turns on Power Animator IK spline twisting. As you turn the
                  twist manipulator at the end joint, the start joint twists slightly with the
                  other joints.
                  With this option off, the start joint doesn’t twist. Use the roll manipulator at
                  the start joint to turn the start joint.
                  You can also set this option after you create the IK spline handle by selecting
                  the IK spline handle and displaying the Attribute Editor. To display the
                  Attribute Editor, select Window→Attribute Editor.

                  Twist Type
                  This option specifies how the twist occurs in the joint chain:
              •   Linear twists all parts evenly.
              •   Ease In twists more at the end than the start.
              •   Ease Out twists more at the start than the end.



270   Using Maya: Animation
                                                         Posing and Animating Skeletons
                                                                    Using IK spline handles


          •   Ease In Out twists more at the middle than at either end.
              You can also set Twist Type after you create the IK spline handle by
              selecting the IK spline handle and displaying the Attribute Editor. To
              display the Attribute Editor, select Window→Attribute Editor.

Setting attributes after creating the IK spline handle
              After you create an IK spline handle, you can specify settings for several
              attributes.

              To set attributes after creating the IK spline handle:
          1   Select the IK handle.




                                                                                                 Animation
                                                                                                 Character
          2   Choose Window→Attribute Editor to display the Attribute Editor.
          3   Expand the IK Solver Attributes section.
              The following attributes are displayed:
              Solver Enable   Turning this off disables the IK spline solver. If you’ve
                              bound skin to the joint chain, turn this option off before
                              returning the joint chain to the bind pose.
                              While this option is on, avoid moving individual joints or
                              you might encounter unexpected joint rotations. You also
                              cannot move or rotate the IK handle.
                              Be aware that the IK spline solver doesn’t operate if there
                              are joint limits on any of the joints controlled by an IK spline
                              handle.

              Offset          See the following note.
              Roll            See “Animating the joint chain” on page 261.
              Twist           See “Animating the joint chain” on page 261.
              Twist Type      See the following note.
              Root on Curve   See the following note.
              Root Twist
              Mode            See the following note.




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Using IK spline handles



                                                       Note
                  Twist Type, Root on Curve, and Root Twist Mode are available when you
                  select Skeletons→IK Spline Handle Tool-Ë.
                  In the Attribute Editor, Offset affects the joint chain only if you turn on
                  Root on Curve. For details on these attributes, see “Setting options before
                  creating the IK spline handle” on page 265.


Preventing unwanted start joint flipping
                  The start joint might flip undesirably when you move or rotate a curve or its
                  CVs in some directions or slide the joint chain along its curve. If flipping
                  occurs, it’s likely to do so only in a small range of rotation. The flipping is a
                  normal outcome of IK spline solver calculations.
                  If the orientation of a joint is more than 90 spatial degrees from its zero-
                  rotation value, it might flip unexpectedly as you rotate the curve or CVs. The
                  zero-rotation value is where the joint’s RotateX, RotateY, and RotateZ
                  attributes are 0 (relative to its parent joint’s coordinate system). Flipping is
                  most pronounced near 180 degrees.

                                                          Joint is at its zero-
                                                          rotation value.




                                                         Unwanted start joint rotation might
                                                         occur in the half-spherical region.
                                                         Flipping is pronounced in the
                                                         conical region.



                  You can prevent start joint flipping in most cases by positioning joints
                  appropriately when you create the joint chain. When you create each joint
                  after the start joint, position it roughly in its rest position—the average
                  position of its entire range of motion.




272   Using Maya: Animation
                                                Posing and Animating Skeletons
                                                           Using IK spline handles


    If you’ve positioned joints appropriately and joint flipping is still a problem,
    try parenting the start joint to another joint or to a transform node. See
    “Auto Create Root Axis” on page 268 and “Auto Parent Curve” on page 268.
    Unexpected start joint flipping might also occur when you animate a joint
    chain along its curve, for instance, when you slide a snake along a motion
    path. To prevent flipping in such cases, do these steps.

    To prevent flipping when a joint chain slides down its curve:
1   Select Skeletons→IK Spline Handle Tool-Ë to display the Tool Settings
    window.
2   Turn off Root on Curve, Auto Parent Curve, Auto Create Curve, and Snap
    Curve to Root.




                                                                                        Animation
                                                                                        Character
3   Turn on Auto Create Root Axis.
4   Select the start joint, then the end joint, and then the curve you’ve created.
    This creates the IK spline handle with a parent transform node above the
    start joint. In a subsequent step you’ll put the node on a motion path that
    prevents the start joint flipping.
5   Select the parent transform node, then Shift-click the curve.
    To select the parent transform node, drag a selection box around the start
    joint.
6   Select Paths→Attach to Path-Ë.
    The Attach to Path Options window appears.
7   Turn on Start/End.
8   For the Start Time and End Time, enter the frame range for the joint chain’s
    motion.
    The parent transform node and its child joint chain will move from the start
    of the curve to the end of the curve in the specified frame range.
9   Turn on Follow.
    If the curve has a 3D looping shape, you might also need to turn on Normal
    for the Up Direction to avoid unwanted flipping.
10 Leave other options at the default settings.
11 Click the Attach button.




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Tips for working with IK spline handles


                     When you play the animation, the parent transform node and joint chain
                     move along the curve path. The movement will likely be free of unexpected
                     flipping. However, flipping is unavoidable in some complex paths.
                     Note that you can still roll and twist the joint chain with the IK handle’s roll
                     and twist manipulators for additional control.

Working with soft body curves
                     If you change an IK spline curve to a soft body, you can add dynamic forces
                     to change the curve’s motion. For example, you can connect turbulence to
                     the curve to create random, erratic motion. See Using Maya: Dynamics for
                     details.


Tips for working with IK spline handles
                     This section provides tips for working with IK spline handles on most
                     characters. Subsequent topics offer suggestions specific to the type of
                     character and motion you’re creating.
                 •   To ensure the joint chain moves smoothly when you animate the curve,
                     create many joints close to each other (with short bones).
                 •   Create a simple curve with no sharp bends to help make the joint chain
                     move smoothly when you animate the curve. Use a small number of CVs.
                 •   When you add an IK spline handle to the skeleton of most creatures—
                     including fish and snakes moving along a motion path—parent each IK
                     spline start joint to a transform node or parent joint that’s not controlled by
                     an IK spline handle. This makes the joint chain move with the
                     transformations of the parent while avoiding unexpected joint flipping. See
                     “Preventing unwanted start joint flipping” on page 272 for details.
                     If you’re working on a character with a root joint that rotates little, for
                     instance, a swaying tree, you don’t need to parent the start joint to a
                     transform node or joint. The start joint can serve as the character’s root joint.
                 •   For a character such as a fish or snake moving along a motion path, if you
                     create a handle that starts at a skeleton’s root, turn on Auto Create Root
                     Axis when you create the IK spline handle. This prevents unexpected joint
                     flipping as you animate the automatically created parent transform node
                     along a motion path. Also turn off Auto Parent Curve.




274    Using Maya: Animation
                                                 Posing and Animating Skeletons
                                                Tips for working with IK spline handles


    If you create a handle that starts at a joint other than the skeleton’s root, turn
    on Auto Parent Curve and turn off Auto Create Root Axis so the handle’s
    curve and start joint move with the transformations of the parent joint.
•   When you manipulate a tail or neck parented to a spine, avoid moving the
    first CV of the curve for the tail or neck. Move the second CV minimally,
    preferably only along an imaginary line extending straight out from the end
    of the spine. Manipulate the other CVs freely. This technique ensures that
    the skin flows naturally where the spine meets the tail or neck.
•   To prevent unexpected results, Maya doesn’t let you overlap the same joint
    with two IK spline handles.
•   Do not parent the curve to the start joint. This creates a dependency graph
    loop that causes the start joint to chase the curve as the curve moves. To




                                                                                          Animation
                                                                                          Character
    detect such loops, use the MEL cycleCheck -all command described in the
    online MEL documentation.
•   Do not parent the curve to a transform node that would use that same curve
    as a motion path. In other words, don’t turn on Auto Create Root Axis and
    Auto Parent Curve if you plan to put the transform node on that curve. This
    creates a dependency graph loop.




                                                       Using Maya: Animation      275
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Tips for working with IK spline handles


Working with human skeletons
                      Because a human spine often twists, turns, and bends, an IK spline handle is
                      ideal for controlling it. For example, you can position the handle’s start joint
                      one joint hierarchically below (and positionally above) the skeleton’s root
                      joint. This causes the IK spline joint chain to move with the root’s movement
                      without unexpected joint flipping.




                                                      IK spline
                                                      handle



              IK spline
              handle
                                                                  Start joint

                                                                   Root joint




                                                                  Zoomed view of image on left




276    Using Maya: Animation
                                                        Posing and Animating Skeletons
                                                       Tips for working with IK spline handles


Working with animal skeletons
           Because an animal’s tail, back, and neck twist and turn independently,
           multiple IK spline handles are ideal for controlling them.


                                                          This skeleton has three IK spline
                                                          handles: on the tail, back, and
                                                          neck. The handles give precise
                                                          control of the spine.
                                         Handle


                                              Handle




                                                                                                 Animation
                                                                                                 Character
                                                                        Handle



                                                              Pelvic
                                                              region




           Here’s a close-up of the pelvic region of the preceding skeleton:

             Handle
                                             Handle




                                               Close-up of previous
                                               image’s pelvic region



           Note that you can use two rather than three handles for skeletons: one for
           the tail and one for the neck and back combined.



                                                              Using Maya: Animation       277
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Tips for working with IK spline handles


                     The start joint of the tail’s handle and the start joint of the back’s handle are
                     near the position of the skeleton’s root, but one joint below the root in the
                     skeleton’s hierarchy. This causes the IK spline joint chains to move with the
                     root’s movement without unexpected joint flipping.
                     If you use this approach, turn on Auto Parent Curve when you create the
                     handles. This ensures the curve and joints move with the transformation of
                     the root.
                     For most creatures, using only one handle for the tail, back, and neck won’t
                     give you adequate control.

Working with sinuous motion on skeletons
                     IK spline handles are useful for animating land or sea creatures that move in
                     sinuous or undulating patterns, for example, snakes, fish, and seals. The
                     skeleton’s root location is crucial for achieving the desired motion.
                     To animate a creature that glides smoothly along a path without abrupt
                     direction changes at the head or tail, put the root of the skeleton at the
                     character’s tail end.
                     Turn on Auto Create Root Axis to prevent unexpected joint flipping as you
                     transform the automatically created parent transform node. Also turn off
                     Auto Parent Curve. An example skeleton follows:




                                                  Handle


                                                                                  Handle
                                                                   Handle

                             Handle




                                            Handle

                                                                   The skeleton’s
                                                                   root is at its tail.




278    Using Maya: Animation
                                           Posing and Animating Skeletons
                                          Tips for working with IK spline handles


Though not visible in the preceding figure, a parent transform node appears
hierarchically above the start joint of the handle on the spine.
If the creature’s head or tail moves abruptly, put the skeleton’s root between
the spine’s midpoint and tail, for instance, near the pelvic region:



                Handle

                              Handle


                               Handle




                                                                                    Animation
                                             Handle




                                                                                    Character
      Handle

                                                  Handle



                    Handle        The root is in the
                                  pelvic region.




                Handle


                                                 Handle




                                        Handle



  Handle
                             Close-up of previous
                             image’s pelvic region


                                                     Using Maya: Animation   279
Posing and Animating Skeletons
Animating IK chains


                  Each handle’s start joint in the figure is separated from the root by one joint.
                  None of the IK spline handles pass through the root. This causes the IK
                  spline joint chains to move with the root’s movement without unexpected
                  joint flipping.


Animating IK chains
                  You can animate IK chains by keyframing or by using motion capture data.

Keyframing
                  For information on keyframing, please see Using Maya: Animation, Part 1:
                  Keyframe, which describes the tasks and tools for keyframing, including how
                  to set keys, edit key options, use the Graph Editor, use the Dope Sheet, and
                  use the Playblast window.
                  Please note the following keyframing tips for character animation:
              •   Set a minimum number of keys
              •   Use the Channel Box

                  Set a minimum number of keys
                  You can set a key for every transformation attribute in a scene. However, in
                  character animation, most expert users find that setting a minimum number
                  of keys assures the best use of system resources. They only key
                  transformation attributes that they want to be sure will be interpolated
                  between frames. For example, if only the transformation attribute for
                  translation along the X-axis of an IK handle’s goal has changed, expert users
                  will save a key for only that transformation attribute, not the entire IK
                  handle.

                  Use the Channel Box
                  In addition to the selections from the Keys pull-down menu, many expert
                  users often use the Channel Box to set keys for particular transformation
                  attributes. For example, if you select the Translate X channel and then press
                  the right mouse button, you can choose Key Selected to save a key for that
                  channel only. (Note that in the Channel Box, transformation attributes are
                  identified as channels.)




280   Using Maya: Animation
                                                    Posing and Animating Skeletons
                                                                 Animating IK chains


Motion capture
           For information on motion capture, please see Using Maya, Animation, Part 4:
           Constraints and Motion Capture. You can have motion capture data drive the
           IK handle’s goals, thereby posing the IK chains.




                                                                                          Animation
                                                                                          Character




                                                          Using Maya: Animation     281
Posing and Animating Skeletons
Animating IK chains




282   Using Maya: Animation
13   Skinning Skeletons

     Skinning skeletons is the process of binding a geometry to a skeleton so that
     the skeleton’s actions can deform the geometry. A geometry can be either a
     non-uniform rational B-spline (NURBS) geometry whose points are control
     vertices (CVs), or a polygonal geometry whose points are vertices. Once
     bound, the geometry becomes the skeleton’s skin. In effect, the skeleton’s
     skin provides the shape of the character’s surface. The skin moves as the
     skeleton’s joints move, because during skinning the geometry’s points (CVs




                                                                                     Animation
     or vertices) are identified as skin points and organized into skin point sets




                                                                                     Character
     that are bound to the skeleton’s joints.




     This chapter explains skinning. Skinning skeletons includes the following:
 •   “Understanding skinning” on page 284
 •   “Binding by closest point” on page 285
 •   “Binding by partition set” on page 287
 •   “Binding multiple objects as skin” on page 288
 •   “Returning to bind pose” on page 289


                                                      Using Maya: Animation    283
Skinning Skeletons
Understanding skinning


               •   “Displaying skin point set colors” on page 290
               •   “Editing skin point sets” on page 290
               •   “Detaching and reattaching skin” on page 290
               •   “Animating with skin and skeleton groups” on page 292
                   Note that skinning skeletons often requires use of the Set Editor. If you are
                   not familiar with the Set Editor, please refer to Using Maya: Hypergraph, Sets,
                   and Expressions.


Understanding skinning
                   Skin is a geometry that has been bound to a skeleton, and skinning is the
                   process of binding a geometry to a skeleton. After you’ve built a skeleton
                   and exercised how that skeleton can be posed and animated, you are ready
                   to give the skeleton some skin. First, pose the skeleton so that it fits the
                   geometry properly. Next, bind the geometry to the skeleton, making the
                   model the skeleton’s skin. This skin provides the surface of your character.
                   In Maya, there are two ways to skin a skeleton:
               •   Closest point skinning
               •   Partition set skinning

Closest point skinning
                   In binding by closest point, the geometry’s points (CVs or vertices) are
                   automatically organized into skin point sets based on the proximity of each
                   point to a joint. For each joint with a bone, a skin point set is created that
                   includes the points that are closest to the given joint. The points are then
                   identified as skin points, with each skin point being a member of only one
                   skin point set. In Maya, a collection of sets that can have no members in
                   common is called a partition. In organizing the geometry’s points for
                   binding, Maya partitions them into skin point sets. Because skin point sets
                   can have no members in common, a skin point cannot be bound to more
                   than one joint. In binding by closest point, Maya creates the skin point sets
                   for you. You can edit the sets after they are created to fine-tune the binding
                   of individual skin points.




284   Using Maya: Animation
                                                                        Skinning Skeletons
                                                                       Binding by closest point


Partition set skinning
            If the geometry has its points (CVs or vertices) organized into a partition
            whose sets you want to bind to joints, you can bind by closest partition.
            During modeling, you can partition a geometry’s points (CVs or vertices)
            into sets. A geometry that has the same number of sets as the skeleton has
            joints can be bound to the skeleton by partition set. In binding by partition
            set, a geometry’s already existing partition sets are bound to the skeleton’s
            joints as skin point sets. Each partition set is bound to the nearest joint as a
            skin point set.

Skin point set colors




                                                                                                  Animation
                                                                                                  Character
            Whether you bind by closest point or by partition set, Maya assigns each
            skin point set a color. The points in a given skin point are displayed in the
            set’s color. You can also have the skin point set’s joint be displayed in the
            skin point set’s color.

Bind pose
            After you’ve given the skeleton some skin, whe posed and animated the skin
            will deform based on the skeleton’s action. The only pose in which the skin
            is not deformed relative to the original geometry is the bind pose, which is the
            pose the skeleton was in when you bound the geometry to it.

Skin detachment and reattachment
            You can detach and reattach the skeleton’s skin at any time. Expert users
            detach and reattach when they want to add or remove a skeleton’s joints,
            change the skeleton’s bind pose, do some more modeling on the skin, or
            detach and then bind a different geometry for the skin.


Binding by closest point
            In binding by closest point, Maya automatically creates jointClusters for each
            joint, and distributes the points closest to each joint into that joint’s
            jointCluster set. Binding by closest point is the most common way to skin a
            skeleton.




                                                               Using Maya: Animation       285
Skinning Skeletons
Binding by closest point


                      If you plan to bind additional skins to the skeleton at a later time, you will
                      want to be able to return easily to the pose at which the first skins were
                      bound (the bind pose). Maya saves bind pose information for joints at which
                      you bind the skin, but not joints without skin.
                      Binding to the skeleton from the bottom of the skeleton’s action hierarchy
                      can make it difficult to return the skeleton to its bind pose. The easiest way
                      to ensure that you can return to the bind pose is to always bind from the top
                      of the hierarchy downwards. In cases where you wish to concentrate on the
                      lower part of the skinning first, it is best to bind simplistic substitute skins to
                      the upper part of the skeletal hierarchy to ensure that Maya saves bind pose
                      information for the entire skeleton. Late, you can delete the substitute skins
                      when you are ready to bind the actual skin.

                      To bind by closest point:
                 1    Select the geometry and skeleton.
                      If you are binding to the complete skeleton, select any joint. Maya will
                      understand that you want to bind the geometry to the entire skeleton
                      hierarchy that corresponds to the joint you have whose joint you have
                      selected.
                      If you are binding to selected joints only, explicitly select each joint that you
                      want to bind to.
                      Note that you can attach more than one geometry at a time. Select all the
                      geometries that you want to bind to the skeleton by clicking on one and then
                      Shift-clicking the others to select them.
                 2    Select Skinning→Bind Skin-Ë.
                      The Bind Skin Options window is displayed.
                 3    In Bind to, choose Complete Skeleton or Selected Joints.
                 4    Click Coloring on to color the joints according to the colors assigned to the
                      skin point sets.
                 5    In Bind Method, click Closest Point.
                 6    At the bottom of the Bind Skin Options window, click Bind.
                      The geometry binds to the skeleton. Maya puts the geometry’s points (CVs
                      or vertices) into skin point sets, and each set is controlled by the jointCluster
                      of the closest joint. The jointCluster name will correspond to the name of its
                      joint. For example, if a joint is named elbow, the corresponding jointCluster
                      will be named elbowCluster1.


286    Using Maya: Animation
                                                                      Skinning Skeletons
                                                                     Binding by partition set


           When you first bind the skin, all cluster percentages will be set to 1.0, giving
           the skin a rigid look around the joints. You can apply lattice or jointCluster
           flexors to smooth the transition about the joints, or modify the cluster
           percentages directly using the Set Editor.
           Note that because the skin is bound to the skeleton, the skin’s transformation
           attributes are locked. If you try to manipulate the transformation attributes,
           the manipulator appears gray, indicating the attributes are locked. If you
           decide you want to modify the geometry that you’ve bound to the skeleton
           as its skin, you must first unbind the skin from the skeleton. After you’ve
           modified the geometry, you can then rebind it to the skeleton.
       7   Exercise the skeleton to see how the skin point sets have been created. Note
           how the skin point sets move with the joints to which they are bound. You




                                                                                                Animation
                                                                                                Character
           might want to edit skin point set membership. To edit set membership, see
           Using Maya: Hypergraph, Sets, and Expressions.


Binding by partition set
           In binding by partition set, Maya binds a geometry’s existing partition sets
           to a skeleton. The number of sets should equal the number of joints with
           bones. For information on creating partitions in Maya, see Using Maya:
           Hypergraph, Sets, and Expressions.

           To bind by partition set:
       1   Select the geometry and the skeleton or the specific joints to you wish to
           bind.
       2   Select Skinning→Bind Skin-Ë
           The Bind Skin Options window is displayed.
       3   In Bind to, choose Complete Skeleton or Selected Joints.
       4   Click Coloring on to color the joints according to the colors assigned to the
           skin point sets.
       5   In Bind Method, click Partition Set.
           In the Partition window, select the name of the partition you wish to bind.
           Only partitions composed of point sets are valid for binding by partition.
           Default Maya partitions such as the renderPartition and layerPartition are
           not valid for binding since they contain sets of objects, not points.
       6   At the bottom of the Bind Skin Options window, click Bind.


                                                             Using Maya: Animation      287
Skinning Skeletons
Binding multiple objects as skin


                      Maya binds the selected partition’s sets to the skeleton, with each set bound
                      to the nearest joint.
                      Note that because the skin is bound to the skeleton, the skin’s transformation
                      attributes are locked. If you try to manipulate the transformation attributes,
                      the manipulator appears gray, indicating the attributes are locked. If you
                      decide you want to modify the model that you’ve bound to the skeleton as
                      its skin, you must first unbind the skin from the skeleton. After you’ve
                      modified the geometry, you can then rebind it to the skeleton.
                 7    Exercise the skeleton to see how the skin point sets have been created. Note
                      how the skin point sets move with the joints to which they are bound. You
                      might want to edit skin point set membership. To edit set membership, see
                      Using Maya: Hypergraph, Sets, and Expressions.


Binding multiple objects as skin
                      Maya allows you to bind many objects as skin. You can attach new objects as
                      skin at any time. There are two ways to attach additional objects to a
                      skeleton which already has a bound skin: using the bind skin menu, or using
                      set editing tools.

                      Binding additional objects with the Bind Skin menu:
                      When you add new objects as skin, the skeleton must be in the same position
                      that was in when you bound the original skin. This position is called the
                      bind pose. The following section contains more details on returning the
                      skeleton to the bind pose.
                      Once the the skeleton is at the bind pose, follow the bind by closest point
                      instructions to bind additional skins to the skeleton.

                      Binding additional objects using set membership:
                      A second way to attach new skins is with the Set Editor by adding points to
                      existing jointClusters. If you choose to attach new skins with set editing
                      tools, note that if the skeleton is not at the bind pose, the new skins will
                      immediately be deformed by the skeleton as soon as they are added to the
                      jointCluster’s set. If this deformation is not desired, move the skeleton to the
                      bind pose before adding the points into the jointCluster’s set.




288    Using Maya: Animation
                                                                     Skinning Skeletons
                                                                     Returning to bind pose


Returning to bind pose
           The pose a skeleton is in during skinning is called the bind pose. When you
           pose a character, the skeleton’s action causes skin deformations. The only
           pose that does not cause skin deformations is the bind pose; when the
           skeleton is in the bind pose, the skin is in the same shape that it was in when
           it was a geometry.
           Yo will want to return the skeleton to the bind pose before binding new skin
           geometries. You will also want to return the skeleton to the bind pose before
           adding lattice flexors.

           To return a skeleton to its bind pose:




                                                                                              Animation
                                                                                              Character
       1   Select any joint on the skeleton.
       2   Choose Skinning→Go to Bind Pose.
           The skeleton assumes the pose it had during skinning, when the geometry
           was bound to the skeleton.
           If possible, the skeleton assumes the pose it had during skinning, when the
           geometry was bound to the skeleton. It may not be possible for Maya to
           move the skeleton to the bind pose. Constraints, keyframed IK Handles, IK
           Handles using the spline solver, locked attributes and expressions can all
           create situations where a skeleton is unable to go to the bind pose. If the
           skeleton is unable to move to the bind pose, you will receive an error
           message saying: Error: Could not reach bindPose due to
           constraints, expressions, or keyframed handles. When this
           happens, a quick way to allow the skeleton to reach the bind pose, is to
           disable the source of the conflict:
       3   Choose Modify→Disable Nodes→All.
           Maya only stores the bind pose for joints which have skin attached. It is best
           to always bind skin from the top-down so that there are no joints above the
           bound skin that do not have skin attached. Otherwise, going to the bind
           pose may cause your skeleton or skin to become distorted. For this reason , it
           is best to have all of the skeleton and skins displayed when you go to the
           bind pose. If either the skeleton or the skins are distorted, undo, and
           consider resetting the skeleton’s bind pose to a new position.

           To reset a skeleton’s bind pose:
           You might want to reset a skeleton’s bind pose. You can do so as follows:



                                                            Using Maya: Animation      289
Skinning Skeletons
Displaying skin point set colors


                  1   Select any joint on the skeleton.
                  2   Choose Skinning→Preserve Skin Groups→Detach Skeleton.
                      The skin on the skeleton will move its undeformed position. If the
                      undeformed position is not appropriate for the new bind pose, position the
                      skin based on the new bind pose.
                  3   Choose Skinning→Preserve Skin Groups→Reattach Skeleton.
                      The new bind pose will be set at the current postion of the skeleton.


Displaying skin point set colors
                      Maya assigns each skin point set a color. When the points (CVs or vertices)
                      in a skin point set are displayed, the points are displayed in the assigned
                      color.

                      To display the skin point set colors:
                  1   Select the skin.
                  2   If the skin is from a NURBS geometry, choose Display→ NURBS
                      Components →CVs. If the skin is from a polygonal geometry, choose
                      Display→Polygon Components→Vertices. If the skin is a lattice geometry,
                      choose Display→Object Components→Lattice Points.


Editing skin point sets
                      You can edit skin point sets by using the Set Editor. For information about
                      the Set Editor, please refer to Using Maya: Hypergraph, Sets, and Expressions.


Detaching and reattaching skin
                      Occasionally, you might want to modify the skeleton, reset the bind pose, or
                      do some further modeling on the skin. To do so, you first need to detach the
                      skin from the skeleton. When you finish editing the skeleton or modeling the
                      skin, you can reattach the skin to the skeleton.
                      You can detach the skin in two modes:
                  •   Detach
                  •   Preserve Skin Groups - Detach


290    Using Maya: Animation
                                                                        Skinning Skeletons
                                                                Detaching and reattaching skin


             Typical reasons for using Detach include the following:
         •   You no longer want the geometry to act as a skin.
         •   You plan to change the topology of the skin geometry before reattaching.
         •   You want to reset the skin groups and percentage values to their default.
             Typical reasons for using Preserve Skin Groups - Detach include the
             following:
         •   You do not want to lose the current skin groups and percentage values.
         •   You want to reset the bind pose on the skeleton.
         •   You want to modify the skeletal hierarchy.
             Important: In order to reattach the skin while preserving skin groups, you




                                                                                                 Animation
                                                                                                 Character
             must detach the skin in preserve skin groups mode. If you detach the skin
             using the standard detach option, you must reattach the skin by
             reperforming the bind skin operation.

Detaching skin without preserving skin groups and
percentages
             To detach skin without perserving skin groups and percentages:
         1   Select the skin(s) you want to unbind.
         2   Choose Skinning→Detach Skin.
             The Detach Skin Options window is displayed.
         3   From History, choose Delete History, Keep History, or Bake History.
             The Delete History option will unbind the skin, move it to its undeformed
             position, and delete any unused jointClusters. The Keep History option will
             unbind the skin, and move it to its undeformed position, but will not delete
             unused jointClusters. The Bake History option will unbind the skin without
             moving it to its undeformed position, and delete unused jointClusters.
         4   Click the Coloring check-box to set whether to remove joint colors.
         5   At the bottom of the Detach Skin Options window, choose Detach to detach
             the skin.
             Unless you use the Bake History option, the skin will move to its uneformed
             location. The skin’s transformation attributes (translate,rotate, and scale) will
             be unlocked. Unused jointCluster’s in the skin’s history will be deleted
             unless you use the Keep History option.


                                                               Using Maya: Animation      291
Skinning Skeletons
Animating with skin and skeleton groups


Detaching skin while preserving skin groups and
percentages
                     To detach skin while preserving skin groups and percentages:
                1    Select a joint in the skeleton or explicitly select the joints which you wish to
                     detach.
                2    Choose Skinning→Preserve Skin Groups→Detach Skeleton or
                     Skinning→Preserve Skin Groups→Detach Selected Joints based on how
                     much of the skeleton you wish to detach.
                     The skin affected by the detached joints will move to its undeformed
                     position. Its transformation attributes (translate, rotate, and scale) will be
                     unlocked so that you can reposition it. To reattach the skin with its old
                     percentages and groups, use the Preserve Skin Groups - Reattach technique.

Reattaching skin while preserving skin groups and
percentages
                     You can only reattach the skin using this method if you detach the skin
                     using the Preserve Skin Groups - Detach options. If you detach the skin
                     using the Detach Skin method, your skin groups and percentages were
                     deleted so you should the basic Bind Skin operation to reattach the skin.

                     To reattach skin while preserving skin groups and percentages:
                1    Select the skeleton or explicitly select the joints which you wish to reattach.
                2    Choose Skinning→Preserve Skin Groups→Reattach Skeleton or
                     Skinning→Preserve Skin Groups→Reattach Selected Joints based on how
                     much of the skeleton you wish to reattach.


Animating with skin and skeleton groups
                     After skinning, create a group for your character that includes the character’s
                     skeleton and skin. Having a group that includes everything that your
                     character consists of can greatly ease the management of the character within
                     an animation, particularly when you have many characters in an animation.
                     You can easily view everything a character’s group can include from the
                     Hypergraph. For more information on using the Hypergraph, please see
                     Using Maya: Hypergraph, Sets, and Expressions.



292    Using Maya: Animation
                                                             Skinning Skeletons
                                            Animating with skin and skeleton groups


    To group skin and skeleton:
1   Select a skeleton and its skin.
2   Choose Edit→Group.
    A group for the character is created. Note that this group node should only
    be used for organizational purposes. It should not be used to translate,
    rotate, or scale the character. Moving the group node causes the skin to get
    doubly transformed since it is transformed once by the skeleton and a
    second time by the group node.




                                                                                      Animation
                                                                                      Character




                                                    Using Maya: Animation      293
Skinning Skeletons
Animating with skin and skeleton groups




294    Using Maya: Animation
14   Using Flexors

     Maya offers a wide variety of deformer tools for creating deformations.
     Flexors are high-level deformer tools for deforming a skeleton’s skin; their
     effects can be linked to the actions of the skeleton.




                                                                                      Animation
                                                                                      Character
     For more information about Maya’s basic deformer tools, please see Using
     Maya: Animation, Basic Deformers.
     This chapter describes flexors. Using flexors includes the following:
 •   “Understanding flexors” on page 296
 •   “Creating lattice flexors” on page 301
 •   “Positioning lattice flexors after creation” on page 302
 •   “Editing joint lattice flexor attributes” on page 302
 •   “Editing bone lattice flexor attributes” on page 313
 •   “Creating sculpt flexors” on page 324
 •   “Editing sculpt flexor attributes” on page 325

                                                       Using Maya: Animation    295
Using Flexors
Understanding flexors


                •   “Joint-driven sculpting” on page 325
                •   “Creating cluster flexors” on page 326
                •   “Editing cluster flexor attributes” on page 328
                •   “Editing with cluster flexor manipulators” on page 328


Understanding flexors
                    Flexors are high-level deformers that deform skin based on how a skeleton
                    moves. There are three types of flexors:
                •   Lattice flexors (joint lattice flexors and bone lattice flexors)
                •   Sculpt flexors (joint sculpt flexors and bone sculpt flexors)
                •   Cluster flexors (joint cluster flexors only)

Lattice flexors
                    Lattice flexors are tools for deforming the skin around joints and the bones
                    of joints. They can smooth or wrinkle skin around joints and provide muscle
                    definition around bones. You could use a joint lattice flexor to ease and
                    smooth the skin around a joint as it bends, or you could use a bone lattice
                    flexor to show bulging muscles around the bones of joints.




296    Using Maya: Animation
                                                             Using Flexors
                                                        Understanding flexors




                                                                                Animation
                                                                                Character
Skin bending around joint without lattice flexor (note creases)




                                               Using Maya: Animation     297
Using Flexors
Understanding flexors




                        Skin bending around joint with lattice flexor (note smoothed crease)

Sculpt flexors
                    Sculpt flexors provide a way to create various types of bulges and dips in a
                    character’s skin.




298    Using Maya: Animation
                                                                             Using Flexors
                                                                        Understanding flexors




                                                                                                 Animation
                                                                                                 Character
            Sculpt flexors are ideal for deformations such as muscle bulges, knee cap
            action, or elbow cap action. You can create sculpt flexors at joints (joint sculpt
            flexors) or at the bones of joints (bone sculpt flexors).

Cluster flexors
            Cluster flexors can provide realistic smoothing effects by allowing you to
            control the points in a skin point set around a joint with varying percentages
            of influence.




                                                               Using Maya: Animation      299
Using Flexors
Understanding flexors




                    To understand cluster flexors, you need some background on the role of the
                    basic cluster deformers in the skinning process. When you skin a skeleton,
                    the skin points are organized into a partition of sets called skin point sets. A
                    skin point set is created to correspond to each joint and bone combination.
                    Also automatically created for each skin point set is one of Maya’s basic
                    deformers, the cluster deformer. Cluster deformers that enable skinning are
                    called joint cluster deformers. A joint cluster deformer is what glues a skin
                    point set to a joint-and-bone combination so that the skin moves with the
                    skeleton. A joint cluster deformer is like a basic cluster deformer except that
                    it acts specifically on a skin point set. (For more information on basic cluster
                    deformers, please refer to Using Maya: Animation, Basic Deformers.)
                    Cluster flexors are high-level tools that provide you with a way to
                    manipulate joint cluster deformers. Cluster flexors can be created only at
                    joints (joint cluster flexors only) because they control joint cluster deformers.




300    Using Maya: Animation
                                                                                Using Flexors
                                                                          Creating lattice flexors


Creating lattice flexors
            Lattice flexors create a lattice deformer around a joint (joint lattice flexor) or
            bone (bone lattice flexor). The flexor’s effect on the skin around the joint or
            bone can be driven by the action of a joint.
            When you create a lattice flexor, the lattice’s reset (base) position
            corresponds to the bind pose.
            To edit a joint lattice flexor, see “Editing joint lattice flexor attributes” on
            page 302.
            To edit a bone lattice flexor, see “Editing bone lattice flexor attributes” on
            page 313.




                                                                                                     Animation
                                                                                                     Character
            To create a lattice flexor at a joint or bone:
        1   Put the skeleton in bind pose by clicking any joint or bone and choosing
            Skinning→Go to Bind Pose.
            It’s possible to create a flexor on a skeleton that’s not in the bind pose, but
            it’s not recommended—you might get unexpected results.
        2   Select the joint or joints on which you want to create a joint flexor. To create
            a bone flexor, select the parent joint of the bone. To create flexors on all joints
            or bones, select any joint on the skeleton.
        3   Choose Skinning→Create Flexor... .
            The Create Flexor window is displayed.
        4   From the Flexor Type: pull-down menu, choose lattice.
        5   To create one or more joint lattice flexors, use the Joints box. In the Joints
            box, click At Selected Joint(s) to create flexors only at the selected joints, or
            click At All Joint(s) to create flexors at all the skeleton’s joints.
        6   To create one or more bone lattice flexors, use the Bones box. In the Bones
            box, click At Selected Bone(s) to create flexors only at the bones of the
            selected parent joints, or click At All Bone(s) to create flexors for all the
            bones.
        7   To specify the divisions of the lattice, use the Lattice Options box. The
            default is 2 S divisions, 5 T divisions, and 2 U divisions. You can enter new
            numbers for the divisions or use the sliders. The greater the number of
            divisions, the smoother the deformation effect; the smaller the number of
            divisions, the faster the performance.



                                                                Using Maya: Animation          301
Using Flexors
Positioning lattice flexors after creation


                   8   Click Position the flexor if you want to adjust the location of the lattice
                       flexor before closing the Create Flexor window.
                   9   If you would like to move, rotate, or scale the flexor without worrying about
                       deforming the skin, you can do so now. Click Position the Flexor. Then
                       choose one of the transform tools (move, rotate, or scale) and change the
                       flexor’s position.
                   10 To create the lattice flexor(s), click OK.
                       Once you have created the lattice flexors, you edit them to control how they
                       deform the skin. To edit joint lattice flexors, see “Editing joint lattice flexor
                       attributes” on page 302. To edit bone lattice flexors, see “Editing bone lattice
                       flexor attributes” on page 313.


Positioning lattice flexors after creation
                       To position a lattice flexor after creation:
                   1   Put the skeleton in bind pose by selecting it and choosing Skinning→Go to
                       Bind Pose.
                   2   Select the lattice group from the Outliner.
                       The lattice group is the highest-level lattice in the Outliner. If you open this
                       lattice (the default name is lattice followed by a number), you’ll see the lattice
                       that deforms the skin underneath it (the default name is deformed followed
                       by a number).
                   3   Select a transform tool.
                       The manipulator of the selected tool appears on the lattice.
                   4   Move the lattice with the manipulator.


Editing joint lattice flexor attributes
                       The attributes of joint lattice flexors control how the flexors deform the skin
                       around joints. Use the Attribute Editor to edit joint lattice flexor attributes.
                       Editing joint lattice flexor attributes includes:
                   •   “Viewing joint lattice flexor attributes” on page 303
                   •   “Renaming joint lattice flexors” on page 303
                   •   “Editing rounding” on page 305


302     Using Maya: Animation
                                                                                  Using Flexors
                                                             Editing joint lattice flexor attributes


          •   “Editing creasing” on page 303
          •   “Editing length in” on page 306
          •   “Editing length out” on page 308
          •   “Editing width left” on page 310
          •   “Editing width right” on page 311

Viewing joint lattice flexor attributes
              To view joint lattice flexor attributes:
          1   Make sure the skeleton is not in the bind pose.




                                                                                                       Animation
                                                                                                       Character
              Flexors don’t deform skin in the bind pose. To see the effects of flexors, you
              must view the skeleton in another pose.
          2   Select a joint lattice flexor.
          3   Choose Window→Attribute Editor... .
              The Attribute Editor is displayed. In the Attribute Editor, you can modify
              the attributes of lattice flexors on joints to create specific effects.

Renaming joint lattice flexors
              By default, joint lattice flexors are given the name “jointFlexor” with a
              number added at the end. You can change the default name. Using names
              that describe the purpose of the lattice flexor can be helpful when you have a
              complex character with many flexors.

              To rename a joint lattice flexor:
          1   View the joint lattice flexor’s attributes in the Attribute Editor.
          2   In the flexorShape: field, enter a new name.

Editing creasing
              The creasing attribute affects the bulging of a joint’s point groups on the
              inside of a bend. When you enter a creasing value, the flexor points on the
              inside of the bend move inward or outward to change the shape of the
              bulge.
          •   A positive creasing value causes the skin to bulge outward.
          •   A negative creasing value causes the skin to tuck inward.

                                                                 Using Maya: Animation         303
Using Flexors
Editing joint lattice flexor attributes


                        The following figures illustrate positive and negative creasing.




                        Positive creasing effect with joint lattice flexor




                        Negative creasing effect with joint lattice flexor

                        To edit creasing:
                   1    View the joint lattice flexor’s attributes in the Attribute Editor.

304     Using Maya: Animation
                                                                               Using Flexors
                                                          Editing joint lattice flexor attributes


         2   In Creasing, enter a new value or use the slider.
             Note that you can also edit the creasing attribute from the Channel Box.

Editing rounding
             Rounding affects the bulging of a joint’s point groups on the outside of a
             bend. When you enter a rounding value, the flexor points on the outside of
             the bend move outward or inward to change the shape of the bulge.
         •   A positive rounding value causes the skin to bulge outward.
         •   A negative rounding value causes the skin to bulge inward.
             The following figures illustrate positive and negative rounding:




                                                                                                    Animation
             Positive rounding effect with joint lattice flexor                                     Character




                                                              Using Maya: Animation         305
Using Flexors
Editing joint lattice flexor attributes




                        Negative rounding effect with joint lattice flexor

                        To edit rounding:
                   1    View the joint lattice flexor’s attributes in the Attribute Editor.
                   2    In Rounding, enter a new value or use the slider. A positive rounding value
                        causes the skin to bulge outward, and a negative rounding value causes the
                        skin to bulge inward.
                        Note that you can also edit the rounding attribute from the Channel Box.

Editing length in
                        The Length In attribute affects the locations of flexor points along the joint’s
                        point group around the upper bone. When you enter a Length In value, the
                        flexor planes along the upper bone move away from or towards the joint.
                   •    A positive Length In value causes the lattices to move away from the joint,
                        spreading the bend effect up the upper bone.
                   •    A negative Length In value causes the lattices to move towards the joint,
                        making the bend effect more local to the joint.




306     Using Maya: Animation
                                                                   Using Flexors
                                              Editing joint lattice flexor attributes


When you change the Length In value, you modify the regions affected by
the round, crease, and width effects.
The following figures illustrate positive and negative length in effects.




                                                                                        Animation
                                                                                        Character
Positive length in effect with joint lattice flexor




Negative length in effect with joint lattice flexor


                                                  Using Maya: Animation         307
Using Flexors
Editing joint lattice flexor attributes


                        To edit length in:
                   1    View the joint lattice flexor’s attributes in the Attribute Editor.
                   2    In Length In, enter a new value or use the slider. A positive value causes the
                        deformation to spread farther up the bone towards the joint’s parent joint. A
                        negative value causes the deformation to concentrate towards the joint.
                        Note that you can also edit the length in attribute from the Channel Box.

Editing length out
                        The Length Out attribute affects the locations of flexor points along the
                        joint’s point group around the lower bone. When you enter a Length Out
                        value, the lattices along the lower bone move away from or towards the
                        joint.
                   •    A positive Length Out value causes the flexor lattices to move away from the
                        joint, spreading the bend effect down the lower bone.
                   •    A negative Length Out value causes the flexor lattices to move towards the
                        joint, making the bend effect more local to the joint.
                        When you change the Length Out value, you modify the regions affected by
                        the round, crease, and width effects.
                        The following figures illustrate postive and negative length out effects.




308     Using Maya: Animation
                                                                   Using Flexors
                                              Editing joint lattice flexor attributes




                                                                                        Animation
                                                                                        Character
Positive length out effect with joint lattice flexor




Negative length out effect with joint lattice flexor



                                                  Using Maya: Animation         309
Using Flexors
Editing joint lattice flexor attributes


                        To edit length out:
                   1    View the joint lattice flexor’s attributes in the Attribute Editor.
                   2    In Length Out, enter a new value or use the slider. A positive value causes
                        the deformation to spread farther down the joint’s bone. A negative value
                        causes the deformation to concentrate towards the joint.
                        Note that you can also edit the length out attribute from the Channel Box.

Editing width left
                        The Width Left attribute affects the bulging of a joint’s point groups on the
                        left side of a bend. When you enter a Width Left value, the flexor points on
                        the left side of the bend move outward or inward to change the shape of the
                        bulge.
                   •    A positive Width Left value causes the skin to bulge outward.
                   •    A negative Width Left value causes the skin to bulge inward.
                        The following figures illustrate positive and negative width left effects.




                        Positive width left effect with joint lattice flexor




310     Using Maya: Animation
                                                                                  Using Flexors
                                                             Editing joint lattice flexor attributes




                                                                                                       Animation
                                                                                                       Character
              Negative width left effect with joint lattice flexor

              To edit width left:
          1   View the joint lattice flexor’s attributes in the Attribute Editor.
          2   In Width Left, enter a new value or use the slider. A positive value causes
              the skin to bulge outward, and a negative value causes the skin to bulge
              inward.
              Note that you can also edit the width left attribute from the Channel Box.

Editing width right
              Width Right affects the bulging of a joint’s point groups on the right side of
              a bend. When you enter a Width Right value, the flexor points on the right
              side of the bend move inward or outward to change the shape of the bulge.
          •   A positive Width Right value causes the skin to bulge outward.
          •   A negative Width Right value causes the skin to bulge inward.
              The following figures illustrate positive and negative width right effects.




                                                                 Using Maya: Animation         311
Using Flexors
Editing joint lattice flexor attributes




                        Positive width right effect with joint lattice flexor




                        Negative width right effect with joint lattice flexor

                        To edit width right:
                   1    View the joint lattice flexor’s attributes in the Attribute Editor.



312     Using Maya: Animation
                                                                                Using Flexors
                                                            Editing bone lattice flexor attributes


          2   In Width Right, enter a new value or use the slider. A positive value causes
              the skin to bulge outward, and a negative value causes the skin to bulge
              inward.
              Note that you can also edit the width right attribute from the Channel Box.


Editing bone lattice flexor attributes
              To edit bone lattice flexor attributes, use the Attributes Editor. Editing bone
              lattice flexor attributes includes:
          •   “Viewing bone lattice flexor attributes” on page 313
          •   “Renaming bone lattice flexors” on page 314




                                                                                                     Animation
                                                                                                     Character
          •   “Editing length in” on page 314
          •   “Editing length out” on page 316
          •   “Editing width left” on page 318
          •   “Editing width right” on page 311
          •   “Editing bicep” on page 321
          •   “Editing tricep” on page 322

Viewing bone lattice flexor attributes
              To view bone lattice flexor attributes:
          1   Make sure the skeleton is not in the bind pose.
              Flexors don’t deform skin in the bind pose. To see the effects of flexors, you
              must view the skeleton in another pose.
          2   Select a bone lattice flexor.
          3   Choose Windows→Attribute Editor... .
              The Attribute Editor is displayed. In the Attribute Editor, you can modify
              attributes of lattice flexors on bones to create specific effects.




                                                                Using Maya: Animation        313
Using Flexors
Editing bone lattice flexor attributes


Renaming bone lattice flexors
                       By default, bone lattice flexors are given the name “boneFlexor” with a
                       number added at the end. You can change the default name. Using names
                       that describe the purpose of the lattice flexor can be helpful when you have a
                       complex character with many flexors.

                       To rename a bone lattice flexor:
                  1    View the bone lattice flexor’s attributes in the Attribute Editor.
                  2    In the flexorShape: field, enter a new name.

Editing length in
                       The Length In attribute affects the locations of flexor points along the bone’s
                       point group. When you enter a Length In value, the flexor planes move
                       away from or towards the center of the bone.
                  •    A positive Length In value causes the lattices to move away from the center,
                       spreading the bend effect to a greater area of the bone.
                  •    A negative Length In value causes the lattices to move towards the center,
                       making the bend effect more localized.
                       By changing the Length In value, you can lengthen or shorten the bulging
                       created by the other deformation parameters.
                       The following figures illustrate no effect, positive length in effect, and
                       negative length in effect.




314    Using Maya: Animation
                                                                   Using Flexors
                                               Editing bone lattice flexor attributes




                                                                                        Animation
                                                                                        Character
No length in effect with bone lattice flexor




Positive length in effect with bone lattice flexor




                                                  Using Maya: Animation         315
Using Flexors
Editing bone lattice flexor attributes




                       Negative length in effect with bone lattice flexor

                       To edit length in:
                  1    View the bone lattice flexor’s attributes in the Attribute Editor.
                  2    In Length In, enter a new value or use the slider. A positive value causes the
                       deformation to spread away from the center of the bone. A negative value
                       causes the deformation to concentrate towards the center of the bone.
                       Note that you can also edit the length in attribute from the Channel Box.

Editing length out
                       The Length Out attribute affects the locations of flexor points along the
                       bone’s point group. When you enter a Length Out value, the flexor planes
                       move away from or towards the center of the bone.
                  •    A positive Length Out value causes the lattices to move away from the
                       center, spreading the bend effect to a greater area of the bone.
                  •    A negative Length Out value causes the lattices to move towards the center,
                       making the bend effect more localized.
                       By changing the Length Out value, you can lengthen or shorten the bulging
                       created by other deformation parameters.



316    Using Maya: Animation
                                                                  Using Flexors
                                              Editing bone lattice flexor attributes


The following figures illustrate positive and negative length out effects.




                                                                                       Animation
                                                                                       Character
Positive length out effect with bone lattice flexor




Negative length out effect with bone lattice flexor




                                                 Using Maya: Animation         317
Using Flexors
Editing bone lattice flexor attributes


                       To edit length out:
                  1    View the bone lattice flexor’s attributes in the Attribute Editor.
                  2    In Length Out, enter a new value or use the slider. A positive value causes
                       the deformation to spread away from the center of the bone. A negative
                       value causes the deformation to concentrate towards the center of the bone.
                       Note that you can also edit the length out attribute from the Channel Box.

Editing width left
                       Width Left affects the bulging of a bone’s point group on the left side of a
                       bend. When you enter a Width Left value, the flexor points on the left side of
                       the bend move outward or inward to change the shape of the bulge.
                  •    A positive Width Left value causes the skin to bulge outward.
                  •    A negative Width Left value causes the skin to bulge inward.
                       The following illustrate positive and negative width left effects.




                       Positive width left effect with bone lattice flexor




318    Using Maya: Animation
                                                                                Using Flexors
                                                            Editing bone lattice flexor attributes




                                                                                                     Animation
                                                                                                     Character
              Negative width left effect with bone lattice flexor

              To edit width left:
          1   View the bone lattice flexor’s attributes in the Attribute Editor.
          2   In Width Left, enter a new value or use the slider. A positive value causes
              the skin to bulge outward, and a negative value causes the skin to bulge
              inward.
              Note that you can also edit the width left attribute from the Channel Box.

Editing width right
              Width Right affects the bulging of a bone’s point group on the right side of a
              bend. When you enter a Width Right value, the flexor points on the right
              side of the bend move inward or outward to change the shape of the bulge.
          •   A positive Width Right value causes the skin to bulge outward.
          •   A negative Width Right value causes the skin to bulge inward.
              The following figures illustrate positive and negative width right effects.




                                                                Using Maya: Animation        319
Using Flexors
Editing bone lattice flexor attributes




                       Positive width right effect with bone lattice flexor




                       Negative width right effect with bone lattice flexor

                       To edit width right:
                  1    View the bone lattice flexor’s attributes in the Attribute Editor.
                  2    In Width Right, enter a new value or use the slider. A positive value causes
                       the skin to bulge outward, and a negative value causes the skin to bulge
                       inward.
                       Note that you can also edit the width right attribute from the Channel Box.



320    Using Maya: Animation
                                                                               Using Flexors
                                                           Editing bone lattice flexor attributes


Editing bicep
             Bicep affects the bulging of a bone’s point group on the inside of a bend.
             When you enter a Bicep value, the flexor points on the inside of the bend
             move outward or inward to change the shape of the bulge.
         •   A positive Bicep value causes the skin to bulge outward.
         •   A negative Bicep value causes the skin to bulge inward.
             The following illustrate positive and negative bicep effects.




                                                                                                    Animation
                                                                                                    Character
             Positive bicep effect with bone lattice flexor




                                                              Using Maya: Animation         321
Using Flexors
Editing bone lattice flexor attributes




                       Negative bicep effect with bone lattice flexor

                       To edit bicep:
                  1    View the bone lattice flexor’s attributes in the Attribute Editor.
                  2    In the Attribute Editor, choose Extra Attributes.
                  3    In Bicep, enter a new value or use the slider. A positive value causes the skin
                       to bulge outward, and a negative value causes the skin to bulge inward.
                       Note that you can also edit the bicep attribute from the Channel Box.

Editing tricep
                       The Tricep attribute affects the bulging of a bone’s point group on the
                       outside of a bend. When you enter a Tricep value, the flexor points on the
                       outside of the bend move outward or inward to change the shape of the
                       bulge.
                  •    A positive Tricep value causes the skin to bulge outward.
                  •    A negative Tricep value causes the skin to bulge inward.
                       The following illustrate positive and negative tricep effects.




322    Using Maya: Animation
                                                                      Using Flexors
                                                  Editing bone lattice flexor attributes




                                                                                           Animation
                                                                                           Character
    Positive tricep effect with bone lattice flexor




    Negative tricep effect with bone lattice flexor

    To edit tricep:
1   View the bone lattice flexor’s attributes in the Attribute Editor.
2   In the Attribute Editor, choose Extra Attributes.



                                                      Using Maya: Animation        323
Using Flexors
Creating sculpt flexors


                  3   In Tricep, enter a new value or use the slider. A positive value causes the
                      skin to bulge outward, and a negative value causes the skin to bulge inward.
                      Note that you can also edit the tricep attribute from the Channel Box.


Creating sculpt flexors
                      You can create sculpt flexors at joints (joint sculpt flexors) or at the bones of
                      joints (bone sculpt flexors). You can use sculpt flexors to make skin slide
                      more realistically over a joint, or use them on bones to create bulges or dips
                      as the joint moves.




                      To create a sculpt flexor:
                  1   Put the skeleton in bind pose by selecting any joint and choosing
                      Skinning→Go to Bind Pose.
                      It’s possible to create a sculpt flexor on a skeleton that’s not in the bind pose,
                      but it’s not recommended—you might get unexpected results.
                  2   Select the joint or joints on which you want to create the flexor. If you want
                      to create a bone sculpt flexor, select the bone’s parent joint. To create flexors
                      on all joints or bones, select any joint of the skeleton.


324    Using Maya: Animation
                                                                               Using Flexors
                                                                 Editing sculpt flexor attributes


        3   Select Skinning→Create Flexor.
            The Create Flexor window is displayed.
        4   From the Flexor Type: pull-down menu, choose sculpt.
        5   Click the boxes under Joints and Bones to indicate where you want to
            position the flexor or flexors: at selected joints or all joints, and at selected
            bones or all bones.
        6   Set the Max Displacement, Dropoff Distance, Dropoff Type, Mode, and
            Inside Mode options as you would for a basic sculpt object.
            These options are described in Using Maya: Animation, Basic Deformers.
        7   Click OK to create the flexors on the joints and bones you indicated.




                                                                                                    Animation
                                                                                                    Character
            Once you have created the sculpt flexors, you manipulate them to deform
            the skin when the joints move. See “Joint-driven sculpting” on page 325.


Editing sculpt flexor attributes
            To edit sculpt flexors:
        1   Select the flexor you want to modify.
        2   Open the Attribute Editor by selecting Window→Attributes.
            The sculpt flexor’s attributes are displayed.
        3   Change the attributes as desired. These attributes are described in Using
            Maya: Animation, Basic Deformers.


Joint-driven sculpting
            To have a joint’s attributes drive the sculpt deformation, use the Set Driven
            Key tool. (For more information on Set Driven Key, please refer to Using
            Maya: Animation, Keyframe.)

            To set joint-driven sculpting:
        1   Put the skeleton in bind pose by selecting any joint and choosing
            Skinning→ Go to Bind Pose.
        2   Select the sculpt flexor.
        3   Select Keyframe→Set Driven Key... .


                                                                Using Maya: Animation       325
Using Flexors
Creating cluster flexors


                      The Set Driven Key window is displayed.
                      A default driver and driver attribute are loaded for you. The driver is the
                      joint whose motion controls the animation of the sculpt deformation. The
                      Attribute is the transform of driver joint that the sculpt deformation is
                      specifically keyed to.
                      Driver attributes include the following:
                      autoGuide       The guide axis (or axes) correspond to the axes the joint is
                                      permitted to rotate in (based on the Joint Limits setting in
                                      the Attribute Editor). Auto Guide is the default and works
                                      well in most cases.
                      rotateX         The guide axis is the joint’s X-axis.
                      rotateY         The guide axis is the joint’s Y-axis.
                      rotateZ         The guide axis is the joint’s Z-axis.
                      maxXYZ          The guide axes are the joint’s X-, Y-, and Z-axes.
                  4   In the browser, select the attribute you want to animate.
                  5   Set the key by clicking Key.
                      The key for the bind position of the character is created.
                  6   Select the handle of the joint chain, move the joint chain, and continue
                      setting keys by clicking Key.


Creating cluster flexors
                      Cluster flexors allow you to control how smoothly skin moves around joints
                      during posing and animating.




326    Using Maya: Animation
                                                                      Using Flexors
                                                               Creating cluster flexors




                                                                                          Animation
                                                                                          Character
    During skinning, cluster deformers are automatically created to bind skin
    point sets to joints. These cluster deformers that bind skin point sets to joints
    are called joint clusters. Joint clusters indicate their deformation effects on
    skin point sets by their drop-off values. The drop-off values are percentage
    values that indicate the range and magnitude of the deformation effects. By
    controlling the range and magnitude of drop-off, you can control the
    smoothness of skin around a joint.
    Cluster flexors provide a way for you to manipulate the drop-off directly.
    Rather than having to specify actual values for the percentages, you can use
    the cluster flexor’s manipulators to edit the deformation effects.

    To create a cluster flexor:
1   Put the skeleton in bind pose by selecting any joint and choosing
    Skinning→Go to Bind Pose.
2   Select the joint (or joints) on which you want to create the flexor.
3   Choose Skinning→Create Flexor... .
    The Create Flexor window is displayed.
4   From the Flexor Type: pull-down menu, choose jointCluster.



                                                      Using Maya: Animation       327
Using Flexors
Editing cluster flexor attributes


                  5    Click the boxes under Joints to indicate where you want to position the
                       flexor or flexors: at selected joints or at all joints.
                       Except for simple cases, you will probably want to adjust the cluster to
                       position it and change the percentages for the best effect on the skin bending
                       around the joint.
                  6    Click Create.
                       Cluster flexors are created at the selected joints.
                  7    Open the Hypergraph by choosing Window→Hypergraph... .
                       The Hypergraph will indicate the cluster flexor(s) as a “jointFlexor” with a
                       number appended. The number indicates the order in which the flexors have
                       been created.
                       When you select the cluster flexor, note that a “J” is displayed near the
                       cluster flexor’s joint.


Editing cluster flexor attributes
                       To edit cluster flexors:
                  1    Select the cluster flexor you want to edit.
                  2    Open the Attribute Editor by selecting Window→Attribute Editor... .
                       In the Attribute Editor, you can edit the attributes of the cluster flexor, the
                       cluster flexor’s shape, and the joint cluster deformer (the cluster deformer
                       that binds skin point sets to joints). The cluster flexor’s attributes folder is
                       identified as “jointFlexorn,” the cluster flexor’s shape attributes folder is
                       identified as “jointFlexor_Shape,” and the joint cluster deformer (the cluster
                       deformer that binds skin point sets to joints) attributes folder is identified as
                       “JointnClustern.”
                  3    Edit the attributes as desired. Note that the attributes of cluster deformers
                       are described in Using Maya: Animation, Basic Deformers.


Editing with cluster flexor manipulators
                       You can use the cluster flexor’s manipulators to edit the deformation effects
                       of joint clusters. A cluster flexor’s manipulators include of pair of rings.




328    Using Maya: Animation
                                                               Using Flexors
                                      Editing with cluster flexor manipulators




                                                                                 Animation
                                                                                 Character
Cluster flexor manipulator rings
Each ring includes two manipulators: a diamond manipulator and a radial
manipulator.




                                              Using Maya: Animation      329
Using Flexors
Editing with cluster flexor manipulators




                                             Diamond
                                             manipulator




                      Diamond manipulator (selected)
                      Located at the center of the ring, the diamond manipulator controls the
                      range of smoothing. The diamond manipulator controls the range of drop-
                      off of the joint clusters acting on the skin point sets bound to the current
                      joint and the current joint’s parent joint.




330    Using Maya: Animation
                                                                      Using Flexors
                                             Editing with cluster flexor manipulators




                                                        Radial
                                                        manipulator




                                                                                        Animation
                                                                                        Character
    Radial manipulator (selected)
    Located on the ring, the radial manipulator controls the magnitude of
    smoothing. The radial manipulator controls the magnitude of drop-off of the
    joint clusters acting on the skin point sets bound to the current joint and the
    current joint’s parent joint.

    To edit with the cluster flexor manipulators:
1   If you have just created the cluster flexor, you need to choose to have the
    cluster flexor manipulators displayed. In the Hypergraph, select the cluster
    flexor (identified as “jointFlexorn”). Open the Attribute Editor; from Display,
    click on Display Handle. A cross-shaped mark is displayed at the center of
    the joint, near the “J” that identifies the cluster flexor.
2   Select the joint with the Show Manipulator Tool.
    The cluster flexor manipulators are displayed.
3   Be sure the joint is not in the bind pose. Flexors do not provide deformation
    effects when the skeleton is in the bind pose. By having the joint in some
    other pose, you can see the effects of your editing.
4   To edit the range of smoothing, select one of the diamond manipulators.
5   Use the left mouse button to click and drag the diamond manipulator
    towards or away from the joint.
    The range of smoothing changes as you drag the manipulator.

                                                     Using Maya: Animation      331
Using Flexors
Editing with cluster flexor manipulators


                 6    To edit the magnitude of smoothing, select one of the radial manipulators.
                 7    Use the left mouse button to click and drag the radial manipulator towards
                      or away from the joint.
                      The magnitude of smoothing changes as you drag the manipulator.
                      Note that you can also edit the drop-off values of joint clusters from the
                      Attribute Editor. The Upper Value of the current joint’s joint cluster and
                      Lower Value of the parent joint’s joint cluster are controlled by radial
                      manipulators. The Upper Bound of the current joint’s joint cluster and
                      Lower Bound of the parent joint’s joint cluster are controlled by the diamond
                      manipulators. For total smoothing, the values, which are expressed as
                      percentages, should be equal 100.
                      Editing which skin points are in which skin point sets can also help to
                      control smoothing effects.




332    Using Maya: Animation
                                                                                                        Index




A                                   C                                     D
animating                           characters                            dampening
     characters 11, 27                  animating 27                         joints 67
     IK chains 124                      deforming 25                      Degrees of Freedom 52, 60
     keyframing 124                     flexors 25                        dependency graph loops
     motion capture 125                 geometry 12                          IK spline 112, 119
     necks, tails, spines 103           modeling 12                       diamond manipulator 173
     with skin and skeleton             skeletons 14
                                                                          Disconnect Joint 49
      groups 136                        skinning 22, 127
attributes                          child joints 16, 33
     editing joints 55
     setting IK spline handle 115
                                    closest point
                                        binding by 130
                                                                          E
Auto Create Curve 113               cluster flexors 25, 143               end effectors 76, 79
Auto Create Root Axis 112, 122          creating 171                         displaying 84
Auto Joint Limits 54                    editing attributes 172            end joints 35, 74, 76, 78
Auto Joint Orient 53                    editing with manipulators 175
Auto Parent Curve 122                   manipulators 172
Auto Simplify Curve 113             Connect Joint 46                      F
Autopriority 87                     control vertices (CVs) 22
                                                                          fish
                                    creating
                                                                               animating with IK spline 118,
                                        cluster flexors 171
                                                                                122
B                                       IK chains 83
                                        IK handles 82                     flexors 25, 140
                                        IK spline handle 103                   cluster flexors 25, 143
ball joints 52, 60
                                        joint chains 36                        lattice flexors 25, 140
Bicep deformation 165
                                        joints 36                              sculpt flexors 25, 142
bind pose 133
                                        lattice flexors 145               flipping
    reseting 133
                                        parent transform with IK               eliminating in rotate plane
    returing to 133
                                          spline 112                            (RP) solver IK handles 101
binding by closest point 130                                                   preventing IK spline start
                                        sculpt flexors 168
binding by partition set 131                                                    joint 116
                                    Curve Editing Tool 105
binding multiple objects 132                                              flipping in motion path
                                    curves
bone lattice flexors 145                auto-creating with IK spline           preventing IK spline start
bones 14                                  handle 113                            joint 117
    bone lattice flexors 145            auto-simplifying with IK spline   forward kinematics 20, 70
    compensating scale 54, 64             handle 113
                                                                                                                Index




                                        IK spline handle 103
                                        transforming IK handle 109        G
                                                                          geometry 12
                                                                             skin 22
                                                                             skinning 127


                                                                                 Using Maya: Modeling    333
Index



goal                               IK spline handle 103              joint cluster points 23
   displaying 84                       animating sinuous             joint clusters 23
goal’s axis                              motion 122                  joint lattice flexors 145
   displaying 84                       auto-creating curve 113
                                                                     joint limits 64
goals 77, 79                           auto-parenting curve 112
                                                                     Joint Orient 63
                                       creating 103
                                       curve 103                     Joint Tool 36
                                                                     joints 14, 32
H                                      human spines 120
                                       manipulating curve CVs 105,       Auto Joint Limits 54
handle vectors 77, 79                    119                             Auto Joint Orient 53
                                       motion path 117                   ball joints 52
handle wires 76, 78
                                       offset 108                        child joints 16, 33
human spines                                                             compensating scale 54, 64
                                       parenting to transform or
   IK spline handle 120                                                  dampening 67
                                         joint 118
                                       rolling 106                       Degrees of Freedom 52, 60
                                       selecting 107                     disconnecting 49
I                                      setting keys 106                  editing attributes 55
                                       sliding joint chain 107           editing joint limits 64
IK chains 35
                                       snapping curve to start           end joints 35, 74
    animating 124
                                         joint 113                       inserting 41
    Autopriority 87
                                       soft body on curve 118            joint chains 17, 33
    creating 83
                                       tail, back, and neck 121          joint lattice flexors 145
    posing 100
                                       tips for using 118                Joint Orient 63
IK handles 14, 20, 35, 74
                                       tool options 109                  limbs 34
    Autopriority 87
                                       twisting 106                      local axis orientation 63
    creating 82
                                   IK systems 98                         parent joints 16, 33
    editing attributes 94
                                       accessing 99                      positioning 40
    editing display 96
                                       creating 98                       Preferred Angle 61
    editing limits 96
                                       renaming 99                       removing 42
    end joints 74
                                       viewing available IK              renaming 58
    Priority 89
                                         solvers 99                      resizing display 40
    setting creation options 85
                                   Insert Joint Tool 41                  root joints 18, 32
    setting PO weight 90
                                                                         Rotate Damp Range 68
    setting weight 89              inverse kinematics 20, 70
                                                                         Rotate Damp Strength 68
    Snap Enable 88
                                                                         Scale Compensate 54
    Solver Enable 88
                                                                         Segment Scale
    start joints 74                J                                       Compensate 64
    Sticky 89                                                            setting creation options 50
                                   joint chain planes 79
IK solvers 21, 35, 75                                                    start joint 35
    editing attributes 97          joint chains 17, 33
                                                                         start joints 74
    IK spline solvers 81               adding to 37
                                                                         Stiffness 62
    multi-chain (MC) solvers 81        creating 36
    rotate plane (RP) solvers 77       inserting joints 41
    single chain (SC) solvers 75       limbs 17



334     Using Maya: Modeling
                                                                                                    Index




K                                   N                                    reference planes 80
                                                                         Remove Joint 42
keyframing 124                      Number of Spans 113, 114             Reroot Skeleton 50
    minimum keys 124                                                     rerooting skeletons 50
    using Channel Box 124                                                rolling
kinematics 70                       O                                         IK spline handle 106
                                                                         root joints 18, 32
                                    offset
                                                                         Root on Curve 107
L                                       IK spline handle 108
                                    overlapping                          Root Twist Mode 114
lattice flexors 25, 140                 IK spline handle joints 119      Rotate Damp Range 68
     bone lattice flexors 145                                            Rotate Damp Strength 68
     creating 145                                                        rotate plane (RP) solvers 77
     editing bone lattice flexor
      attributes 157
                                    P                                         behavior 81
                                                                              end effectors 79
     editing joint lattice flexor   parent joints 16, 33                      end joints 78
      attributes 146                partition set                             goals 79
     joint lattice flexors 145          binding by 131                        handle vectors 79
     positioning 146                partitions 22                             handle wires 78
Length in deformation 150, 158      pelvic region                             joint chain planes 79
Length out deformation 152, 160         positioning skeleton root             plane indicators 80
limbs 17, 34                             in 123                               pole vectors 80
     mirroring 45                   plane indicators 80                       reference planes 80
limits                              PO weight 90                              rotation discs 80
     joint limits 64                                                          start joints 78
                                    points 22
                                                                              twist discs 80
                                        skin point sets 22
                                        skin points 22                   rotation discs 80
M                                   pole vector’s axis                   Rounding deformation 149
                                        displaying 84
Mirror 45
                                    pole vectors 80
Mirror Across 45
                                    posing                               S
Mirror Joint 45
                                        IK chains 100                    Scale Compensate 54
mirroring 43                            sticky posing 102
                                                                         sculpt flexors 25, 142
modeling 12                         Power Animator                           creating 168
motion capture 125                      IK spline twisting in Maya 114       editing attributes 169
motion paths                        Preferred Angle 61                       joint-driven sculpting 169
                                                                                                              Index



    IK spline handle 117            Priority 89                          seals
moving                                                                       animating with IK spline 122
    start joint off IK spline
                                                                         Segment Scale Compensate 64
     curve 111
multi-chain (MC) solvers 81
                                    R                                    selecting
                                                                             IK spline handle 107
    activating 87                   radial manipulator 173


                                                                             Using Maya: Modeling       335
Index



setting keys
    IK spline handle 106
                                    Snap Curve To Root 113
                                    Snap Enable 88
                                                                        V
single chain (SC) solvers 75        Solver Enable 88                    vertices 22
    behavior 77                          IK spline handle 115
    end effectors 76                spline solvers 81
    end joints 76
    goals 77
                                    start joint flipping                W
                                         in motion path 117
    handle vectors 77                                                   Width left deformation 154, 162
                                         preventing IK spline 116
    handle wires 76                                                     Width right deformation 155, 163
                                    start joints 35, 74, 76, 78
    start joints 76
                                    stickiness 102
sinuous motion
    IK spline handle 122            Sticky 89
                                    sticky posing 102
                                                                        Z
skeletons 14, 32
    animating 14                    Stiffness 62                        zero rotation
    building 14, 31                                                        IK spline joint orientation 116
    combining 46
    construction strategies 50      T
    disconnecting 49
    flexors 25                      tips
    mirroring 45                        building skeletons with
                                         grid 32
    posing 14
                                        IK chain length 35
    rerooting 50
                                        IK chains with rotate plane
    skinning 22, 127
                                         (RP) solvers 81
    viewing hierarchy outline 39
                                        IK chains with single chain
skin                                     (SC) solvers 77
    binding 127                         IK spline handle creation 118
    skin point sets 22                  skeletons with many limbs 34
skin point sets 22                      using mirroring to create
    displaying colors 134                limbs 43
    editing 134                     tool options
skin points 22                          IK spline handle 109
skinning 22, 127                    transforming
    binding by closest point 130        IK spline handle curve 109
    binding by partition set 131    Tricep deformation 166
    binding multiple objects 132
                                    twist discs 80
    detaching skin 134
                                        displaying 84
    reattaching skin 134
                                    Twist Type 115
sliding
                                    twisting
    joint chain along curve 107
                                        IK spline handle 106
snakes
    animating with IK spline 118,
      122



336     Using Maya: Modeling

								
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