The Alliance Display Wall in a Box effort provides by juanagui

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									The Alliance Display Wall in a Box effort provides information on how to build and and
use a tiled display wall.

Tiled display walls create a large-format environment for presenting high-resolution
imagery. The output from a collection of projectors is tiled together and projected to a
single display surface. A cluster of modestly priced Linux PCs, augmented with high-
performance graphics accelerator cards, can be used to drive the wall. The Alliance
DisplayWall-in-a-Box effort makes these high-end display systems easier to set up and
use.

The Alliance DisplayWall-in-a-Box is a collaborative effort with contributions from
Argonne National Laboratory, University of Utah, University of Illinois at Urbana-
Champaign, University of Minnesota, Princeton University, Stanford University, and the
National Center for Supercomputing Applications.

This documentation describes DisplayWall-in-a-Box Version 1.0, dated October 31,
2001.



DisplayWall-in-a-Box, v. 1.0                                                     Page 1
CONTENTS

Contents .............................................................................................................................. 2
Introduction......................................................................................................................... 3
Projectors ............................................................................................................................ 4
   Projector Technologies ................................................................................................... 4
   Projector Evaluation Factors........................................................................................... 5
   Minimum Projector Specifications ................................................................................. 7
Projector Positioners ........................................................................................................... 8
Screens .............................................................................................................................. 11
   Screen Evaluation Factors............................................................................................. 11
Shelves .............................................................................................................................. 12
Sample Wall Configurations............................................................................................. 13
   NCSA Configuration.1 (20-tile wall) ........................................................................... 14
   NCSA Configuration.2 (40-tile wall) ........................................................................... 15
   Alliance SC2000 Configuration.................................................................................... 16
   Argonne National Labs ActiveMural............................................................................ 17
   Argonne National Labs MicroMural2 .......................................................................... 18
   UIUC CS Department ................................................................................................... 19




DisplayWall-in-a-Box, v. 1.0                                                                                               Page 2
INTRODUCTION

The Alliance DisplayWall-in-a-Box includes guidelines for building a tiled display wall,
along with a software suite for displaying imagery on the wall. We describe how to build
a wall and connect it to a cluster of Linux PCs. Guidelines for building the wall include
information on choosing machines and graphics accelerators, evaluating projectors, and
selecting screens. Tiled walls must also deal with the challenge of precisely aligning the
projectors so that the output of adjacent tiles matches up properly to create a seamless
image. The Alliance DisplayWall-in-a-Box effort includes suggestions for positioning
projectors and aligning the imagery.

The DisplayWall-in-a-Box software toolkit includes utilities and applications for movie
playback, as well as complete visualization tools that can direct output to a tiled wall. As
part of the overall Alliance strategy for software deployment, the DisplayWall-in-a-Box
software is compatible with the Alliance Cluster-in-a-Box software.




DisplayWall-in-a-Box, v. 1.0                                                       Page 3
PROJECTORS

Projectors are usually the most expensive component of a display wall, so it is important
to choose carefully. Most tiled display walls are built using commodity-level projectors
built for the business presentation market. These are designed to be bright and
lightweight. They are not necessarily designed to give uniform illumination over the light
field, or to project a perfect rectangle. These considerations are important when tiling
multiple projectors together to create a seamless display field. Careful evaluation is
needed to identify models that will perform adequately and produce quality
visualizations.

Projector manufacturers discontinue current models and introduce new models
frequently, making it difficult to simply suggest 1 or 2 models. This section outlines the
basics of projector technologies and lists the factors that should be considered when
evaluating projectors. We also make note of projectors that have been used in existing
tiled display walls.




PROJECTOR TECHNOLOGIES

There are three types of technologies used in contemporary business presentation
projectors. The pros and cons of each technology are summarized in Table 1.




DisplayWall-in-a-Box, v. 1.0                                                       Page 4
 Technology                     Pros                      Cons

 LCD                            uniform illumination      fair contrast
 Liquid Crystal Display         good color                poor black level

 DLP                            high fill factor          sometimes poor uniformity
 Digital Light Processing       good contrast             color wheel artifacts
                                good black level          modulation not camera
                                                          friendly
                                                          major light leak

 DILA                           high resolution           high cost
 Digital Image Light            high fill factor          large
 Amplification                  uniform color             high power consumption
                                good contrast             expensive bulbs
                                good black level

       Table 1. Projector technologies in use today have advantages and
       disadvantages.



PROJECTOR EVALUATION FACTORS
The following evaluation factors should be considered when choosing projectors for a
tiled wall.

Resolution vs. cost
An increasing number of projectors support a resolution of 1280 x 1024, but at a cost that
is considerably more than XGA projectors of 1024 x 768 resolution.

Uniform illumination
The images of the projectors will be placed side by side on the screen and any falloff in
the illumination will be very noticeable. This is particularly apparent in the corners.
Many of the currently available projectors have uniformities greater than 80%. A value of
80% or greater is acceptable for use in a display wall.

Minimal geometric distortion
The images will be placed side by side on the screen and any non-linearity in the edges
will cause overlap or gaps between adjacent images causing geometric distortion. It is
often possible to minimize the distortion by adjusting the zoom on the projector.




DisplayWall-in-a-Box, v. 1.0                                                     Page 5
Low black level
Adjacent projector images may be overlapped on the wall in order to support blending.
This blending makes the edges between projectors less noticeable. Since a projector
always puts out some light, even when showing black, the overlapped area will be
slightly brighter than the rest of the image. Choosing a projector with a low black level
can minimize this effect.

Manual control for zoom and focus
Some projectors come with motorized zoom and focus controls. On these projectors it is
possible for the zoom and/or focus to change when the projector is turned off and on.
This can cause misalignment problems that will need to be constantly corrected. A
manual zoom and focus prevents this problem.

Manual control for color, brightness, white/black level
It is possible that projectors of the same model from the same manufacturer may have
slightly different color responses and brightness levels. It is important to find a projector
that allows the user to control the brightness and contrast of all 3 color channels, and
gamma. The more manual picture controls a projector provides, the more adjustable it
will be resulting in a better visual display.

Serial connection for computer control of power and settings
Some projectors have serial ports on them that can be used to control their operation in
the same way that the IR (infrared) remote does. This capability makes it easier to power
up/down the entire wall and make adjustments to a single projector.

Digital Video Interface
The image generators inside a projector are digital devices. Image quality can benefit
from sending digital video signals to the projector rather than traditional analog signals.

Long lamp life
Lamps typically cost from $300-$700, and have lifetimes of 1000-3000 hrs. Lamps with
a long life will reduce the cost of operating the wall.

Low power
Large arrays of projectors use a large amount of power. Choosing projectors with a low
power requirement will minimize the amount of heat emitted into the room.

Small size and weight
The smaller a projector is, the easier it is to mount and position. Also, the space
requirements are minimized.




DisplayWall-in-a-Box, v. 1.0                                                          Page 6
MINIMUM PROJECTOR SPECIFICATIONS
Resolution
1024x768 (XGA)


Light output
800 lumens or better


Uniformity
80% or better


Manual control for color, brightness, white/black level


Manual control for zoom and focus


Low black level




DisplayWall-in-a-Box, v. 1.0                              Page 7
PROJECTOR POSITIONERS
A significant challenge in building a tiled wall is the requirement that the projectors be
precisely aligned to create a seamless image.

Some walls are built by simply placing the projectors on shelves. It is very, very difficult
to align the projectors under these conditions, although this might work for walls as small
as 2 x 2.

Alliance members have experimented and designed a few devices for positioning
projectors. For example, Figure 1.shows one of the first designs developed, in a
collaborative effort between Princeton University and Argonne National Laboratory.




       Figure 1. This positioner design comes from Princeton University and
       Argonne National Labs. It can be custom machined by your local
       machine shop, working from CAD drawings available from the Alliance.

At NCSA, Vis team members have designed alternate projector positioners that allow for
more precise control over projector alignment. One design uses a collection of extruded
aluminum pieces, hinges, and threaded rods to manipulate the translation and rotation of
the projector image. The aluminum pieces come from www.8020.net. Each positioner
also uses a small front-silvered mirror mounted with finely threaded thumbscrews. The
mirror provides additional controls, especially to rotate the image.




DisplayWall-in-a-Box, v. 1.0                                                       Page 8
The challenge in designing positioning devices is to provide for precise control over the
position and orientation of the projector. Careful alignment is needed to make sure that
the output of each projector lines up properly with adjacent projectors. It is especially
important that the positioner afford control over each degree of freedom. The NCSA
positioner design uses a sliding bearing to slide the projector along the horizontal rail for
that row, in the plane parallel to the display screen. A vertical threaded rod with a hex nut
adjusts the positioner up and down. For larger movements, or for adjusting many
projectors, a power driver is a handy way to deal with the vertical adjustment. The lens
on the projector itself controls the zoom factor of the projector image. The projector
positioner also uses a small mirror mounted on the positioner. The projector points off to
the side, and bounces the image off the mirror towards the rear of the screen. The mirror
is attached to a plate. The mirror mount, attaching the mirror plate to the positioner
assembly, has two finely threaded screws that are used to adjust the angle of the mirror.

The NCSA mirror positioner is shown in Figure 2. NCSA staff designed this mirror
positioner from pieces of extruded aluminum. The projector beam is parallel to the rear
side of the screen, and bounces off the mirror to the screen.. Figure 3 shows a collection
of the positioners used in the 20-tile wall.




       Figure 2. NCSA staff designed this mirror positioner from pieces of
       extruded aluminum. The projector beam is parallel to the rear side of the
       screen, and bounces off the mirror to the screen.




DisplayWall-in-a-Box, v. 1.0                                                        Page 9
       Figure 3. Each of the NCSA mirror positioners is mounted to a custon
       frame. The image is beamed to the mirror and bounces to the rear of the
       screen.




DisplayWall-in-a-Box, v. 1.0                                                 Page 10
SCREENS

A variety of screen materials can be used with a tiled display wall, and some are more
appropriate than others.

Selection criteria focus on materials that optimize the image display from the projector,
the size of material available, and physical stability. For example, most tiled display walls
are rear-projected. In addition, a low gain (amount of light reflected from the screen
surface) and ability to provide good contrast minimize problems associated with projector
alignment.




SCREEN EVALUATION FACTORS

Low gain/diffuse
Compact projectors of the type typically used for display walls are very bright for the size
of image that they project. It is important to get a low gain screen with a wide viewing
angle to obtain the best image. Lenticular screen of the type commonly used with CRT
projectors are not appropriate for a display wall of LCD/DLP projectors.

Black or gray tint
The projectors used for display walls typically have poor black level performance. By
using a black or gray screen, as opposed to a white one, the perceived black level is
reduced.

Physical stability
Three screen types are available when classified by physical stability. These are fully
rigid, semi-rigid, and flexible. Fully rigid screens have very good physical stability and
noise damping but are impractical for large screens and are hard to move. Semi-rigid
screens have good physical stability but often come in panels that allow light leak.
Flexible screens are easy to install and take down but tend to warp with changes in air
pressure. Flexible screen are also available in large sizes.




DisplayWall-in-a-Box, v. 1.0                                                      Page 11
SHELVES

Shelving to hold the projectors is a surprisingly important part of a display wall.
Considering the following factors while choosing shelving material will improve the
appearance and function of the tiled wall.

Stability
The shelves should be as sturdy as possible. If the shelves are not stable enough, simply
bumping them may be enough to knock your carefully adjusted projectors out of
alignment.

Surface Texture
The shelving surface itself needs to be smooth and solid so that the projectors or bases
will sit squarely and securely, and will not easily move.

Adjustability
The capability to adjust the height of the shelves in rather small increments will enable
you to physically align the projected tiles more easily.




DisplayWall-in-a-Box, v. 1.0                                                     Page 12
SAMPLE WALL CONFIGURATIONS

It is very difficult to specify the “ideal” wall configuration. In some cases, a site might
not have a choice about machines, since they might already have a cluster and now they
want to add a display wall. It is also difficult to recommend specific models of projectors
and graphics accelerator cards, since models tend to come and go very quickly.

In the following section, we describe a number of existing display walls, including notes
on the types of machines that are used, the graphics cards, and the projectors. This is
intended to give some general guidelines about how existing walls have been configured.




DisplayWall-in-a-Box, v. 1.0                                                    Page 13
NCSA CONFIGURATION.1 (20-TILE WALL)




    •   Size: 20 tiles, arranged 4 across and 5 high, for 4096 x 3840 pixels
    •   Projectors: NEC VT540, 1024 x 768
    •   Cluster: 20 HP Kayaks, dual Pentium III, 550 MHz, 9 GB and 45 GB IBM
        Deskstar IDE 7200 RPM IDE disks
    •   Memory: 1 GB RDRAM
    •   Graphics accelerator: LeadTek GeForce2 Pro
    •   Front End: Dell Precision 420, dual 1 GHz Pentium III, 1 20 GB SCSI drive, 2
        40 GB IBM DeskStar 7200 RPM IDE disks
    •   Screen: 9 foot high, 12 foot across, flexible, from Stewart Screen
    •   Shelving: Projectors sit on a custom frame, constructed from aluminum
        extrusion from www.8020.net
    •   Positioners: Custom design from aluminum extrusion
    •   First Light: May 2001



DisplayWall-in-a-Box, v. 1.0                                                   Page 14
NCSA CONFIGURATION.2 (40-TILE WALL)
    •   Size: 40 tiles, arranged 8 across and 5 high, for 8192 x 3840 pixels
    •   Projectors: NEC VT540, 1024 x 768
    •   Cluster: 40 HP Kayaks, dual Pentium III, 550 MHz, 9 GB and 60 GB RAID IDE
        7200 RPM IDE disks
    •   Memory: 1 GB RDRAM
    •   Graphics accelerator: Nvidia Quadro Pro
    •   Front End: Dell Precision 420, dual 1 GHz Pentium III, 1 20 GB SCSI drive, 2
        100 GB IBM DeskStar 7200 RPM IDE disks
    •   Screen: 9 foot high, 18 foot across, flexible.
    •   Shelving: Projectors sit on a custom frame, constructed from aluminum
        extrusion
    •   Positioners: Custom design from aluminum extrusion
    •   First Light: November 2001




DisplayWall-in-a-Box, v. 1.0                                                   Page 15
ALLIANCE SC2000 CONFIGURATION




    •   Size: 6 tiles, arranged 3 across and 2 high, for 3072 x 1536 pixels
    •   Projectors: Proxima, 1024 x 768
    •   Cluster: 6 Dell 4100, Pentium III, 1 GHz, 256 MB, 40 GB IDE disks
    •   Graphics accelerators: Nvidia GeForce2
    •   Front end: Dell 4100, Pentium III, 1 GHz, 256 MB, 40 GB IDE disk
    •   Screen: 9 foot high, 12 foot across, flexible, from Stewart Screen.
    •   Shelving: Projectors sit on Gorilla Rack, from local home improvement store.
    •   Positioners: machined locally, based on Argonne/Princeton design.
    •   First Light: November 2000




DisplayWall-in-a-Box, v. 1.0                                                  Page 16
ARGONNE NATIONAL LABS ACTIVEMURAL




    •   Size: 15 tiles, arranged 5 across and 2 high, for 4292 x 1996 pixels
    •   Projectors:Epson 710c, 1024 x 768
    •   Cluster: 15 IBM IntelliStation, Pentium III, 500 MHz, 384 MB SDRAM, 9 GB
        IBM DeskStar 7200 RPM IDE disks, 18 GB Seagate 15000 RPM SCSI disk
    •   Graphics accelerators: Elsa Gladiac 920 (Nvidia GeForce 3 with 64 MB Ram
    •   Front end: IBM IntelliStation, Pentium III, 500 MHz, 384 MB SDRAM, 9 GB
        IBM DeskStar 7200 RPM IDE disks, 18 GB Seagate 15000 RPM SCSI disk
    •   Screen: 8 foot high, 16 foot across, Jenmar Visual System BlackScreen.
    •   Shelving: Projectors sit on Metro wire shelving, from www.metro.com.
    •   Positioners: machined locally, based on Argonne design.




DisplayWall-in-a-Box, v. 1.0                                                   Page 17
ARGONNE NATIONAL LABS MICROMURAL2




    •   Size: 6 tiles, arranged 3 across and 2 high, for 2532 x 1407 pixels
    •   Projectors:Epson 7500c, 1024 x 768
    •   Cluster: 6 IBM IntelliStation, Pentium III, 500 MHz, 384 MB SDRAM, 9 GB
        IBM DeskStar 7200 RPM IDE disks, 18 GB Seagate 15000 RPM SCSI disk
    •   Graphics accelerators: Elsa Gladiac 920 (Nvidia GeForce 3 with 64 MB Ram
    •   Front end: IBM IntelliStation, Pentium III, 500 MHz, 384 MB SDRAM, 9 GB
        IBM DeskStar 7200 RPM IDE disks, 18 GB Seagate 15000 RPM SCSI disk
    •   Screen: 44.5” high, 76” across, Jenmar Visual System BlackScreen.
    •   Shelving: FrameWorld aluminum extrusion, www.frame-world.com.
    •   Positioners: custom design with 6 degrees of freedom.
    •   First Light: November 2000




DisplayWall-in-a-Box, v. 1.0                                                  Page 18
UIUC CS DEPARTMENT




    •   Size: 18 tiles, arranged 6 across and 3 high, for 6144 x 2304 pixels
    •   Projectors:Epson PowerLite 7550c, 1024 x 768
    •   Cluster: 18 Dell dual Pentium III, 500 MHz, 512 MB SDRAM, 4 8 GB SCSI
        disks
    •   Graphics accelerators: Nvidia GeForce2 GTS
    •   Front end: Dell dual Pentium III, 500 MHz, 512 MB SDRAM, 4 8 GB SCSI
        disk
    •   Screen: 6 panels, JenMar Visual System BlackScreen
    •   Shelving: Projectors sit on metro shelving, www.metro.com
    •   Positioners: Chief LCD projector mounts




DisplayWall-in-a-Box, v. 1.0                                                   Page 19

								
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