INTERMEDIATE MODELING for GIS: AT echnical Primer for Advanced by lL5dDRTg

VIEWS: 3 PAGES: 74

									                                Section II: Data Models and Data

    2.1.      GIS data models
    2.2.      Spatial analysis
    2.3.      Surface analysis
    2.4.      USGS digital data




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                 2.1. GIS Data Models
      GIS provides a stable modeling environment
       because of its Cartesian grid
      GIS employs both raster and vector
       methodologies
      Topology facilitates the spatial intersect, a
       function SQL is incapable
      GIS data representations may be either discrete
       or continuous
      Reference frames may be 1, 2, 2½, 3 or 4
       dimensional
      General GIS models may be classified as either
       field, object, or network


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
       What are Geographic Information Systems?
         – Automated means of compiling, storing,
           displaying, and analyzing spatial data
       Three General Capabilities:
         – Computer map—ties map locations to a
           Cartesian grid and thus facilitates the
           construction of mathematical models
         – Bring life to tabular data by consolidating
           information in one place using location as the
           organizational key
         – Facilitates the creation of new information




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
       Mechanics of Building Computer Maps:
         –   Computers do nothing but add and remember
         –   Easily map pictures with x-y coordinates
         –   Building x-y coordinates into a “picture” requires a
             stated data relationship between coordinates
         –   Data may be stored like a photograph or TV picture -
             RASTER where x-y coordinates hold attributes
         –   Data may be stored like a stick drawing of directed
             line segments - VECTOR where lines are assumed to
             connect x-y locations


                                            ……………..
                                            ……………..
                                            ……………..
                                            ……………..

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                 By using the mathematically relationships
                                    between x-y coordinate in terms of
                                 connectivity and proximity, GIS provides
                                   the structure necessary to perform a
                                            “Spatial Intersect”




                                               SQL


       What is contained within a boundary area?
       What is within a distance of a boundary?
       Delete those objects contained within.

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                          Three Methods of Spatial
                                          Intersect:

                                                                                   Cookie Cutters on
                                                                                     Graph Paper


      Connectivity: arc-node topology:
      Area Definition: poly-arc topology:                                             Tabular
      Contiguity: left-right topology:                                            Relationships of
                                                                                    Connectivity
        Asphalt                Concrete           Asphalt         Concrete




                                                                                        Stacked
        Bad                    Good                               Fair


                                                                                      Coordinates
                  48 54                   39      49         66
 25   TLMS 100001         65   0               TLMS 100002                   100




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques             Terra Genesis, Inc.
                                     Cookie Cutters on Graph
                                              Paper
     UPDATE: Merge new features


                    +           =
                                                            CLIP: Cookie cutter inside



                                                                            +       =

       ERASE: Cookie cutter outside


                      +          =



Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
          BUFFER:




                   UNION:



        IDENTITY: Add common                              INTERSECT: Delete areas not
        features from two maps                                common to primary


                     +            =                                     +        =



Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  Topological Relationships

     Connectivity: arc-node topology:
                                                                     Spatial primitives
       – Arcs must connect to other arcs at                             (line work)
         nodes
       – Distinguishes nodes from vertices
     Area Definition: poly-arc topology:
       – Arcs that connect to surround an                                   Topological
         area define a polygon                                                 rules
       – First and last node are always the
         same
     Contiguity: left-right topology:
                                                                              Spatial
       – Arcs have direction
                                                                             Intersect
       – Allows networks to be built
       – Creates left and right polygons



Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques     Terra Genesis, Inc.
                                   Problems with Topology

     GIS is set apart from RDBMS only by its ability to facilitate
      spatial intersect through topology
     Topology isolates GIS from mainstream IT
     Long proven RDBMS tools for version control and rollback
      cannot be applied to GIS venues
     Breach between IT and GIS management and operation

    Topology complicates data storage through complex tabular
     relationships
    The ratio of information to data is so low, it precludes large-scale
     enterprise implementation without additional fixes that further
     separate GIS from mainstream IT
    Low information ratios hinder Internet-enablement and client-
     server optimization


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                 In Large Implementations,
                                 Data must be Tiled:




                     Data Lock-down a Pressing Problem

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  Stacked Coordinates (Dynamic
                                  Location):
                                                                        PolyLine Event DLO
        Step 1: Bring shapes together                              (no measures necessary)
                       Attribute A
                                                 Attribute B


                   0    10   20    30 40 50 60 70 80 90 100 110 120
                                  PolyLineM Route DLO {x,y,z,m} required

        Step 2: Drop Event DLO end points to Route DLO
                       Attribute A
                                                Attribute B



                   0    10   20      30   40    50   60   70       80   90 100 110 120


       Step 3: Read polyLineM as a number line to build intersect
               table            ID#    From     To        Attribute
                                               100001          4        37          A
                                               100001         37        44         A&B
                                               100001         44        70          B




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques    Terra Genesis, Inc.
                                   Continuous Data Models that
                                      do not Store Topology
      Leaner data that need not be tiled, creating a
       continuous data set
      No topology implies attributes maintained with the
       spatial data within an RDBMS and not a dedicated
       GIS
      Spatial data within RDBMS offers temporal version
       control and traditional RDBMS rollback capabilities
      Relegates GIS to RDBMS support duties
      But . . . some mechanism must be devised to
       accomplish spatial intersect and connectivity




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                 The Raster Data Model:

        Pixel size - picture element or tessellation:
          – Larger, less resolution
          – Smaller, more memory & computation intensity
        Pixel shape:
          – Divisible into similar shaped units
          – Distance between centers should be equidistant
        Pixel Representation:
          – Cell value represents the value at the cell’s center
            only
          – Cell value represents the value of the entire cell face




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                     (1) Selecting Pixel Shape:


                         Squares are divisible, but distances are
                            not the same in every direction



           Circles are equidistant, but
                cannot be divided



                 Triangles, Hexagons, Bucky Balls
              You name it! The two design objectives
                      are mutually exclusive


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                     (2) Selecting Pixel Size:

      Cell = 1000 m                     Cell = 100 m                        Cell = 10 m



         oooooooo                         oooooooo                           oooooooo
         oooooooo                         oooooooo                           oooooooo
         oooooooo                         oooooooo                           oooooooo
         oooooooo                         oooooooo                           oooooooo



      Area = 120 ha                   Area = 120 ha                     Area = 120 ha
      Array = 30 x 40                 Array = 300 x 400                  Array = 3000 x 4000
     Count = 1200                    Count = 120 000                    Count = 12 000 000
    Memory = 4.8 kb                 Memory = 480 kb                   Memory = 48 Mb




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  (3) Cell Value Representation:

                   Case I-Value                                     Case II-Value
                  cell center only                                  entire cell face




            Continuous Field                                       Discrete Entities
          Floating Point Raster                                   Categorical Raster
      Interpolation between values                              Interpolation not valid
         No attributes assigned                                  Can attach attributes


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
     Three Classes of Data Models (ways of interpreting
      data values):
       –   FIELD MODEL: a continuous variation of one variable across
           space
       –   OBJECT MODEL: Space is subdivided into functional,
           unique, and discrete units
       –   NETWORK MODEL: Two dimensional representation of one
           dimensional space—up a street, down a street, no node-no
           turn
     How Spatial Data are Classified:
       –   1-D (linear)
       –   2-D (flat map - x,y)
       –   2 ½-D (surface x,y,only one z per x, y pair)
       –   3-D (solid - x,y,z-multiple z per x,y pair)
       –   4-D (temporal - x,y,z,t)

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
        Field Model                       Object Model                         Network
                                                                                Model
       002222333322210                     111111111111111                  111100000000000
       002233777775210                     999111199111111                  000110000000000
       023445578887521                     991111199991111                  000011111111111
       134555789876531                     999911199999111                  000010000010000
       111455788875211                     999999999111111                  000010000010000
       012455788775522                     444444411111111                  000010000010000
       012345777774210                     444444411111111                  000010000011111




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  2.1. GIS Data Models
Why is topology required within vector data models?
What are the constraints associated with topology?

Describe two ways to increase query speeds when vector
topology is required.

What two rules are used to select pixel shape?

Describe interpolation in terms of continuous and
discrete data models.

What is the difference between a solid and a surface
model?

Describe a field model.

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                   2.2. Spatial Analysis:

        The systematic and logical reduction (sifting
         through) of ALL data to find the NEEDED
         information
        Needle in the haystack we deal with daily
        Connect stacked maps with logical operators to
         reduce the available information, or, create new
         information more suited to the task
        LOCATION is used as the disparate integrator
        ASSUMES: correlations and consistencies are
         easier to visualize when data are stored and
         queried spatially


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                 4-classes of Spatial Analysis:

        Spatial Overlay &
       Contiguity Analysis


        Raster Analysis                                        Surface Analysis




                                                                    Network
                                                                    Analysis



Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                 Spatial Overlay & Contiguity
                                 Analysis:

           New maps created from the combination of others
           Light-table gymnastics
           McHarg 101


       A firm seeks land to build a new factory:
            • On a rail line
            • Non-sandy soil
            • Parcel > 2 hectares
            • Parcel price < $12 000 per hectare
            • Population < 2000, > 750/ hectare

       For a liquor license requested at 5th and Elm:
           • List home owners within 500 meters
           • List schools within 2 km
           • List/plot liquor license count within 10 km


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                       Raster Analysis via Map
                                               Algebra



                                   •                               =



                    New raster = in-raster 1 • in-raster 2
                    Where, •, is a mathematical operator

       Arithmetic, (+) (-) (x) (÷)                      Boolean, (TRUE or FALSE)
       Relational, (<) (>) () ()                      Logical, if, then, else



Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                    Local Raster Functions:
    Local raster functions have a
    1:1, cell to cell, correspondence
    between input and output



                                                           Example per cell operators
                                                           are sine, cosine, multiply,
                                                           and divide
                                  Input Raster
                                                           Several rasters may be
                                                           simultaneously examined on a
                                                           per cell basis to return
                                                           statistics for all corresponding
                                                           stacked cell values

                                Output Raster


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  Focal Raster
                                  Functions:
                                                                            Target cell



              Cell
         neighborhood

 Focal functions
 consider adjoining                                                           Input Raster
 cells to the target cell
 to determine the
 output cell value.


These types of functions
      help smooth data.
                                                                            Output Raster




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques    Terra Genesis, Inc.
                                      Zonal Raster Functions


                                                   Target cell
                              Input
                              Raster             Comparison
                                                    zone


                                                Zonal functions require two
                                Zone            rasters. Values from the
                               Raster
                                                secondary zonal raster are
                                                referenced during processing
                                                of each input cell.

                              Output
                              Raster

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                   Global Raster Functions
  Global functions generally produce a new raster that is the
  solution to a problem or spatial equation:
         • Path finding
         • Path finding through a weighted field
         • Surface functions: slope, shading, and shadow
         • Darcy flow and dispersion
         • Multivariate analysis




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  2.2. Spatial Analysis

  What are the four types of spatial analysis?

  What analysis type relies on spatial intersect
  capabilities?

  What is the difference between a raster and a raster
  surface?

  What is the primary purpose of a global raster?

  How can time be viewed in a raster? How about
  randomness? How about either in vector form?

  Describe some raster analysis applications.


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                   2.3. Surface Analysis

       Surface analysis looks at the slope of the line
        between adjacent points of a field model
       Color models and value stretching may be used to
        visualize the shape of a surface
       A zero slope is a horizontal line, and thus a contour
       A negative second derivative is concave down and
        models a water shed divide
       A positive second derivative is concave up and
        bounds a stream bed




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                    Surface Analysis:

        Finding isolines (contours), constant slope between points
        Finding slopes (1st derivatives) between points
        Finding inflexion points (2nd derivatives) between points
        Applying color models and value stretching for display


        Assumes a field model, and                         •   General surface shape
         so interpolation is a valid                       •   Cut and fill
          mathematical operation                           •   Fluid flows
           between point values                            •   Shadows
                                                           •   Visibility and view shed




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                    Raw Surface Data:




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                        RGB Color Model




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  Stretching Data Increases
                                          Contrast




              0             64            128               192             255 value




              0             64            128               192             255 value

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques    Terra Genesis, Inc.
                                   Color Model Application:




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                     The Shape of a Mountain:


                           z
        3000 m


        2000 m


        1000 m


    Sea Level                                                                            x
                                         1km            2 km            3 km


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                                Concave Down Inflection:



                                                            d2z/dx2 < 0
                                                          Local maximum
                                                        water shed boundary

                                                      Concave Up Inflection:
                                                                 d2z/dx2 > 0



                                                              Local minimum
                                                                stream bed

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                          Concave Up:

                                                 dz/dx < 0
                                                d2z/dx2 > 0
                                               energy losing
                                                depositing


                                   Concave Down:

                                                   dz/dx < 0
                                                  d2z/dx2 < 0
                                                 energy gaining
                                                    eroding

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                         Raw Surface Values:

          5       5       5       1       7       7       7       7         7      7

           1      1       1       1       5       5      5       5          5      7

          5       5       5       1       5      7       7       7          5      7

           5      9       5       7       5       7      9       7          5      7

           5      5       5       1       5       7      7       7          5      7

           1      1       1       1       5       5       5      5          5      7

          5       5       5       1       1      1       1       1          1      1

           7      7       7       1       5       5      5       5          5      5



Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques       Terra Genesis, Inc.
                                 Connecting Raw Points with
                                 Lines for Slope Analysis
         5       5      5        1        7       7       7       7         7        7

         1       1       1       1        5       5       5       5         5        7

         5       5       5       1       5        7       7       7         5       7

         5       9       5       7        5       7       9       7         5        7

         5       5       5       1        5       7       7       7         5       7

         1       1       1       1        5       5       5       5         5        7

         5       5       5       1       1        1       1       1         1       1

         7       7       7       1        5       5       5       5         5        5


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques       Terra Genesis, Inc.
                                   Surface Values with Slope = 0:

       5        5        5        1          7        7        7        7      7       7

       1        1         1        1        5        5        5        5       5       7

       5        5        5         1        5        7        7        7       5       7

       5        9         5        7        5        7        9        7       5       7

       5        5        5         1        5        7        7        7       5       7

       1        1         1        1        5        5        5         5      5       7

       5        5        5         1        1        1        1        1       1       1

       7        7         7        1        5        5        5        5       5       5

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                   Extracting and Vectorizing
                                   Contours:




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  Contour Development,
                                  Slope = 0:




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                   Connecting Slope < 0:

       5        5       5         1         7        7        7        7       7       7

       1        1        1        1         5        5        5        5      5        7

       5        5        5        1        5         7        7        7      5       7

       5        9        5        7         5        7        9        7      5        7

       5        5        5        1         5        7        7        7      5        7

       1        1        1         1        5        5        5        5       5       7

       5        5        5        1        1         1        1        1      1       1

       7        7        7        1         5        5        5        5      5        5

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                Flow Direction/Slope Vector Field




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                   Flow Direction:




                     elevation                                  elevation gradient




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                                                                       point
                                                                                     together
                                                                                    stream bed


                                                                                    point apart
                                                                                    water shed



                                                                                    point in line
                                                                                    water flow




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                   Stream Bed Inflection Points:




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                      2.3. Surface Analysis
 What is color/value stretching?

 How is slope defined?

 How are contour lines developed by a computer from a
 surface model?

 What is the mathematical restriction of a surface
 model?

 What may be said about interpolation in a surface
 model?

 Describe a stream and a water shed boundary in terms
 of slope arrows.

Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  2.4. USGS Digital Data

       DEM - Digital Elevation Model
       DOQ - Digital Orthophoto Quadrangle combine
        digital photography with DEMs
       DRG - Digital Raster Graph is a scanned and
        rectified quadrangle map
       DLG - Digital Line Graphs are linear
        transportation ,boundary and hydrographic
        features
       http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/
        ndcdb.html
       http://edcwww.cr.usgs.gov/webglis




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  DEM - Digital Elevation Model

        Digital representations of cartographic
         information consisting of an array of regularly
         spaced elevations
        Created from digitized or scanned cartographic
         map overlays
        Contour lines are scanned into digital form
        Mathematical algorithms parse out and
         interpolate ‘postings’ and a set interval




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                                 DEM Display Techniques


 95 1689 1692 1699 1697 1697 1704 1707 1709 1712 1721 1726 1729 1729
  1728 1727 1726 1726 1726 1726 1726 1727 1726 1725 1723 1720 1717
 1709 1707 1713 1714 1713 1706 1700 1690 1683 1682 1682 1682 1684 16
 80 1692 1692 1693 1691 1700 1705 1712 1713 1706 1695 1677 1674 1670
  1670 1670 1671 1674 1677 1679 1680 1683 1683 1685 1688 1690 1694
 1695 1698 1701 1703 1707 1712 1712 1718 1718 1721 1719 1719 1719 17
 19 1719 1719 1719 1719 1719 1719 1719 1719 1719 1718 1718 1716 1715
  1714 1713 1712 1710 1707 1706 1703 1707 1706 1707 1707 1707 1707
 1708 1708 1708 1708 1708 1707 1708 1704 1702 1701 1701 1701 1701 17
 00 1700 1701 1701 1704 1707 1708 1708 1707 1707 1707 1707 1707 1707
  1707 1707 1707 1707 1705 1705 1703 1702 1696 1691

   1 2 463 1 0.510420000000088D+06 0.462183000000000D+07 0.000
 000000000000D+00 0.156200000000000D+04 0.173000000000000D+04 1686 1686 16
 87 1686 1685 1685 1685 1686 1684 1686 1686 1687 1687 1688 1685 1679
  1677 1673 1676 1677 1681 1683 1686 1689 1690 1693 1696 1700 1706
 1713 1715 1722 1720 1719 1718 1717 1718 1720 1714 1710 1706 1705 17
 02 1700 1696 1690 1688 1689 1690 1692 1694 1695 1700 1703 1708 1717
  1725 1726 1725 1721 1714 1710 1708 1709 1712 1708 1703 1697 1695
 1694 1695 1688 1690 1697 1697 1701 1706 1713 1712 1711 1716 1726 17
 30 1730 1729 1728 1727 1727 1727 1727 1727 1728 1727 1725 1724 1723
  1720 1715 1714 1722 1721 1717 1710 1702 1691 1685 1682 1681 1680
 1680 1677 1682 1692 1687 1675 1683 1687 1706 1706 1704 1690 1676 16
 72 1669 1670 1670 1671 1671 1675 1676 1679 1681 1681 1684 1688 1689

           Raw File
  1692 1693 1695 1699 1700 1701 1704 1711 1718 1721    Gray Scale              Shaded Relief



Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques    Terra Genesis, Inc.
                                STORM KING MOUNTAIN PERSPECTIVE
                                - VIEW FROM SOUTH LOOKING NORTH




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                            DEM Applications

                                                         Sediment transport models
                                                         Slope, aspect, and habitat
                                                          models
                                                         Vegetative analysis
                                                         Land surface
                                                          characteristics
                                                         Water shed analysis
                                                         Animal vs. human conflict
                                                         Fire prevention
                                                         Erosion control


                                                      Old Faithful, WY


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
       Level 1 Before                     Level 1 After                     Level 2 After

                                Mount St. Helens
Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                   Laser Distance and Ranging
                                   (LIDAR)




                                                                 Digital Orthophoto:
                                                                    • 6 inch pixel
                                                                    • 1 m horizontal

                                                        Digital Elevation Model:
                                                           • 2.5 meter horizontal
                                                           • 15 cm vertical


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  Digital Orthophoto Quarter
                                  Quadrangles

      A digital image of an aerial
       photograph in \which
       displacements caused by
       terrain relief and camera tilts
       have been removed
      Created from digitally-
       corrected, scanned aerial
       photographs
      Combine photograph image
       characteristics with map
       geometric qualities




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                          DOQQ Components
                                                                            Digital Orthophoto
    Digitally scanned aerial photograph



            Digital Elevation Model



         Camera Position/Orientation Data




                                                    Automated Rectification Process




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                         DOQQ Characteristics


          •   Black and White or Color-infrared
          •   3.75-minute X 3.75-minute
          •   NAD 83 / UTM Projection
          •   Pixel represents 1 square meter
          •   50 - 300 meter overedge
          •   Header information + binary data




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
           Using the DOQ as a revision
             tool, it is easy to see the
          amount of change displayed by
             the new DLG road layer


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                  DRG - Digital Raster Graph

        Created by scanning a USGS topographic map at
         250 dpi or finer
        Georeferenced to Earth’s surface in UTM
        Used to collect/revise other digital data
        Greticuel screening is removed
        Color quantization to reduce the number of
         colors using RGB model
        Converted to Tagged Image File Format (TIFF)
        Final file size 5-15 MB




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                                        DRG of Grand Tetons



Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
        Leaking Underground
           Storage Tanks




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                        DRG files merged with DEM
                                        Nine quadrangles paneled together
                                        Drainage basin area clipped out


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                      DRG merged with DOQ




                          Used for:
             Resource management
             Data collection/revision
             Environmental assessment




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                          DLG - Digital Line Graph

        Digital vector representations of cartographic
         information
        Derived from hard copy cartographic sources
         materials, aerial photographs, or raster graphic
         products
        Contains a full range of attribute codes
        7.5 minute boundaries, PLSS, transportation,
         hydrography




Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
              Roads
              Hydrography


Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.
                                     2.4. USGS Digital Data
  What sources are currently used for DEM products?
  How will this change in the future?


  How is a DOQ produced?


  If you needed a background for a GIS model, what
  might you consider using?


  What does “ortho” mean?


  If you needed to develop a low-cost GIS from scratch,
  what might you consider using?
Intermediate Modeling for GIS: A Technical Primer for Advanced Techniques   Terra Genesis, Inc.

								
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