BUILDING VIRTUAL REALITY ON A BUDGET
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
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
Wanda pointing device (not vital) $2500
Tracker PC $500
Sound PC $800
Audio amplifier & speakers $1000
Miscellaneous cables, mounts, etc $500
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
Further and more complete information about
building a low-cost VR system can be found at Pape and Anstey's