A Low-Cost Projection Based VR Display
Dave Pape, Josephine Anstey, Greg Dawe

Projection based virtual reality systems have become well
established in application areas such as computational
science, automotive engineering, and chemical
exploration.  These fields are often favored with large
budgets and can afford expensive, advanced displays.  VR
also has applications for art, cultural heritage, and
educational institutions, many of which have much smaller
budgets, or are not able to support and maintain high-end
graphics workstations.  A simpler, more affordable
projection based display system would be valuable for
these institutions.

Currently, worldwide, there are about 5 CAVEs in public
museums which show art and education projects.  Their
popularity with the public and the economics of
throughput mean that relatively large groups are shown
short demonstrations. Because of the limited time it is
unusual for visitors to interact directly with the
experience - very often a museum worker will navigate and
interact for them.  We believe that a cheaper system
would allow visitors longer, more hands-on, and possibly
more intimate experiences of virtual worlds.

This paper describes the construction of a single screen,
passive stereo, VR display based on commodity, or
otherwise low-cost, components.  We compare its quality
with that of high end systems like a CAVE or ImmersaDesk,
and discuss future directions for lower-cost VR systems.

The core elements of the system are three PCs, two LCD
projectors, tracking, and polarized stereo.  The main
computer, for the graphics, is a dual processor Linux PC
with a two-channel 3D video card.  The tracking system is
a PC with a Space Pad, and a wand interactive device. The
audio system is a PC with a generic audio card and
speakers (and optionally a mixer and more expensive
speakers).  All the PCs are connected by Ethernet.  The
stereo display uses circularly polarizing filters for the
two projectors and inexpensive polarized glasses.  As
with most immersive projection systems, we use
rear-projection to allow people to stand very close to
the screen.  Passive stereo in such systems has been
difficult in the past because standard rear-projection
screens do not preserve polarization; after evaluating
numerous screen materials, we have identified one that
produces very little stereo crosstalk (aka ghosting).

In basic performance tests, the low-cost system is
comparable to one using an SGI Onyx. The quality of the
graphics is inferior to high-end systems - aliasing can
be particularly bad with current PC video cards. The LCD
projectors also have lower resolution than high cost CRT
projectors, but are superior in terms of brightness and
contrast. The lightweight passive stereo glasses are less
encumbering, and less fragile, than active glasses.

This prototype system is being used in an undergraduate
media studies course, allowing students to create their
own interactive virtual environments.  We have also
adapted the same technology to create a monoscopic,
multi-screen display for an exhibit at the Smithsonian
Museum.  Future steps will be to expose the full system
to the rigors of a museum or gallery environment, and to
refine it in terms of durability and usability.