eTech & Art
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  Reports from SIGGRAPH 2001


by Ben Wyrick
23 July 2002

Actual reality has proven to be much more affordable than its virtual counterpart. The high cost of creating and maintaining a virtual reality display is a severely limiting factor to most schools and galleries, according to Dave Pape and Josephine Anstey, who conducted an Educators Program workshop entitled "Building an Affordable Projective, Immersive Display."

According to Pape and Anstey, the goal of Virtual Reality (VR) systems is to interactively stimulate all the senses in realtime. Million-dollar VR installations like the groundbreaking CAVE project use multiple walls of projected video, special active-stereo goggles, and high fidelity surround sound. They require powerful, expensive workstations such as those manufactured by Silicon Graphics. CAVE-like environments also need large amounts of floor space for multiple video projectors and all the hardware which accompanies such ambitious projects.

But what if an institution wants to create a VR display without spending a small endowment? Pape and Anstey created an inexpensive VR system at the University of Buffalo.

At the heart of their system is the use of polarized left eye and right eye projections. Two video projectors overlap their images on a single 7' x 5' (2.1 x 1.5 m) projection screen. Each projector uses a circular polarizing filter, which corresponds to circular polarized glasses worn by participants. Circular polarizers were chosen over linear polarizers since the latter tend to distort images when a user's head tilts. To save costs, the filters are affixed to the projectors' lenses with plumbing equipment. One projector sends out an image which can only be seen by the participant's left eye, and similarly for the right eye. The polarizing filters ensure the proper projection is received by the proper eye. This creates a stereoscopic image for the participant, very similar to actual reality. This particular approach avoids the use of expensive active-stereo goggles. Instead, all that is required is a pair of inexpensive polarized glasses.

One drawback of this system is that a special projection screen must be used which preserves the polarization of light. Pape and Anstey have found that Stewart Filmscreen's "Disney Black" screen meets this criterion.

Aside from hardware decisions, software must also be considered. Commercial software can be expensive, but often comes with technical support. The University of Buffalo system uses CAVElib, OpenGL and Performer.

Following is Pape and Anstey's price breakdown for assembling a low-cost VR system:

Dual-processor PC with GeForce4 graphics card $2300

2 InFocus LP530 projectors $7800

2 Extron distribution amplifiers (needed for video signal) $480

Disney black screen and frame $3000

2 circularly polarizing filters $200

10 pairs of polarized glasses $500

Ascension Spacepad electromagnetic tracker $1460

Wanda pointing device (not vital) $2500

Tracker PC $500

Sound PC $800

Audio amplifier & speakers $1000

Miscellaneous cables, mounts, etc $500

Total $21,040


Pape and Anstey add that cheaper systems can be built, but with dubious results. The cost of purchasing or developing software roughly equals the total hardware cost, according to Pape.

Further and more complete information about building a low-cost VR system can be found at Pape and Anstey's website, www.resumbrae.com/info/cheapvr







Photos from SIGGRAPH 2002


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