The StarCAVE, a third-generation CAVE and virtual reality OptIPortal.
- SourceAvailable from: Tom Peterka[show abstract] [hide abstract]
ABSTRACT: Virtual reality (VR) has long been hampered by the gear needed to make the experience possible; specifically, stereo glasses and tracking devices. Autostereoscopic display devices are gaining popularity by freeing the user from stereo glasses, however few qualify as VR displays. The Electronic Visualization Laboratory (EVL) at the University of Illinois at Chicago (UIC) has designed and produced a large scale, high resolution head-tracked barrier-strip autostereoscopic display system that produces a VR immersive experience without requiring the user to wear any encumbrances. The resulting system, called Varrier, is a passive parallax barrier 35-panel tiled display that produces a wide field of view, head-tracked VR experience. This paper presents background material related to parallax barrier autostereoscopy, provides system configuration and construction details, examines Varrier interleaving algorithms used to produce the stereo images, introduces calibration and testing, and discusses the camera-based tracking subsystem.ACM Transactions on Graphics 01/2005; 24(3):894-903. · 3.36 Impact Factor
- J.Acoust.Soc.Am. 01/1993; 93:2764-2778.
- Concurrency and Computation: Practice and Experience. 01/2003; 15:707-725.
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Future Generation Computer Systems 25 (2009) 169–178
Contents lists available at ScienceDirect
Future Generation Computer Systems
journal homepage: www.elsevier.com/locate/fgcs
The StarCAVE, a third-generation CAVE and virtual reality OptIPortal
Thomas A. DeFantia,∗, Gregory Dawea, Daniel J. Sandinb, Jurgen P. Schulzea, Peter Ottoa, Javier Giradoc,
Falko Kuestera, Larry Smarra, Ramesh Raoa
aCalifornia Institute for Telecommunications and Information Technology (Calit2), University of California San Diego (UCSD), United States
bElectronic Visualization Laboratory (EVL), University of Illinois at Chicago (UIC), United States
cQualcomm, Inc., United States
a r t i c l ei n f o
Received 19 February 2008
Received in revised form
18 July 2008
Accepted 22 July 2008
Available online 17 August 2008
CAVE, Computer-supported collaborative
a b s t r a c t
A room-sized, walk-in virtual reality (VR) display is to a typical computer screen what a supercomputer
is to a laptop computer. It is a vastly more complex system to design, house, optimize, make usable, and
maintain. 17 years of designing and implementing room-sized ‘‘CAVE’’ VR systems have led to significant
new advances in visual and audio fidelity. CAVEs are a challenge to construct because their hundreds
of constituent components are mostly adapted off-the-shelf technologies that were designed for other
uses. The integration of these components and the building of certain critical custom parts like screens
involve years of research and development for each new generation of CAVEs. The difficult issues and
compromises achieved and deemed acceptable are of keen interest to the relatively small community of
VR experimentalists, but also may be enlightening to a broader group of computer scientists not familiar
with the barriers to implementing virtual reality and the technical reasons these barriers exist.
The StarCAVE, a 3rd-generation CAVE, is a 5-wall plus floor projected virtual reality room, operating
at a combined resolution of ∼68 million pixels, ∼34 million pixels per eye, distributed over 15 rear-
projected wall screens and 2 down-projected floor screens. The StarCAVE offers 20/40 vision in a fully
horizontally enclosed space with a diameter of 3 m and height of 3.5 m. Its 15 wall screens are newly
developed 1.3 m × 2 m non-depolarizing high-contrast rear-projection screens, stacked three high,
with the bottom and top trapezoidal screens tilted inward by 15◦to increase immersion, while reducing
stereo ghosting. The non-depolarizing, wear-resistant floor screens are lit from overhead. Digital audio
sonification is achieved using surround speakers and wave field synthesis, while user interaction is
provided via a wand and multi-camera, wireless tracking system.
© 2008 Elsevier B.V. All rights reserved.
A key criterion for VR is the provision of a ‘‘immersive’’ display
with significant tracked stereo visuals produced in real time at
larger angle of view than forward-looking human eyes can see.
Immersion can be provided by head mounted displays and often
is. Another means for immersion is the room-sized projection-
based surround virtual reality (VR) system, variants of which
have been in development since at least 1991 [1–3]. The first
CAVE1prototype was built in 1991, showed full scale (3m3) in
∗Corresponding author. Tel.: + 1 312 996 3002; fax: +1 312 413 7585.
E-mail addresses: firstname.lastname@example.org, email@example.com (T.A. DeFanti),
firstname.lastname@example.org (G. Dawe), email@example.com (D.J. Sandin), firstname.lastname@example.org
(J.P. Schulze), email@example.com (P. Otto), firstname.lastname@example.org (J. Girado),
email@example.com (F. Kuester), firstname.lastname@example.org (L. Smarr), email@example.com
1The name CAVETMwas coined by the lead author of this paper for the VR room
being built at at the Electronic Visualization Laboratory (EVL), University of Illinois
public at SIGGRAPH’922and SC’92, and then CAVEs were built
for the National Center for Supercomputing Applications, Argonne
National Laboratory, and The Defense Advanced Research Projects
Agency. In the past 17 years, hundreds of CAVEs and variants have
been built in many countries. Software called ‘‘CAVElib’’  was
developed and is still widely in use.
The first generation CAVE used active stereo (that is 96–160 fps
field-sequential images separated by glasses that synchronously
blink left and right) to maintain separate images for the left and
right eyes. Three-tube cathode ray tube (CRT) Electrohome ECP
and then Marquee projectors (with special low-persistence green
phosphor tubes) were used, one per 3 m2screen, at a resolution
of 1280 × 1024 @ 120 Hz, thus displaying about the equivalent of
at Chicago (UIC), which was subsequently commercialized by the company that is
now Mechdyne, Corporation.
2Michael Deering of Sun Microsystems, Inc. exhibited a 3-wall similar system
for one user called the Portal at SIGGRAPH’92 . The 3-wall+floor CAVE at
SIGGRAPH’92 allowed multiple users.
0167-739X/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
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T.A. DeFanti et al. / Future Generation Computer Systems 25 (2009) 169–178
Fig. 1. The StarCAVE from above, looking down on a RNA protein rendering. The still camera taking the picture is not being tracked so the perspective is skewed, but this
image shows the floor as well as the walls and shows some of the effects of vignetting and abnormally severe off-axis viewing.
20/140 to 20/200 visual acuity.3Besides providingan experience
of ‘‘low vision’’,4the first CAVEs were relatively dim (the effect was
like seeing color in bright moonlight5), and somewhat stuttering
(the networked Silicon Graphics, Inc. (SGI) workstations, one per
projector, could maintain only about 8 updates of a very modest 3-
Ascension, Inc. Flock of Birds electromagnetic tethered trackers
were used to poll the 6 degree-of-freedom (DOF) position of the
user’s head and hand. There were three rear-projected walls and a
down projected floor, which gave a then novel complete feeling
of room-sized immersion. The screen frame was made of non-
magnetic steel to decrease interference with the tracker, and the
screen was a grey flexible membrane screen stretched over cables
in 2 corners. About 85% of the cost of the first generation CAVE was
in the 5 SGI Crimson workstations, later the 4-output 8-processor
A second-generation CAVE was developed by EVL in 2001,6
featuring Christie Mirage DLP 1280 × 1024 projectors that are
7 times brighter7than the Electrohomes of the first generation,
although 5 times the cost. Users’ color perception got much
better because of the brighter projectors delivering adequate
light to their eyes’ color receptors. Since chip-based projectors
(LCD, LCOS, DLP) do not have the numerous analog controls
on sizing that the CRT projectors did, there is no available
electronic adjustment on modern projectors for keystoning and
other distortions. Mechanical optical alignment requires precision
of frame fabrication, projector mounts, and the flatness and
squareness of the projector image through the lens to achieve
3Calculated by assuming 100 pixels/ft from 10’ away giving 6.84 arc min/pixel,
or ∼20/137. At this quality in vehicle interior simulations, for example, the
VR scene typically is). The metric equivalent of 20/20 is 6/6; 20/200 is 6/60. Randy
Smith of GM Research says, in an unpublished technical report, that GM’s 2.5 m2
CAVE’s acuity is (was) 20/200 .
4In typical drivers’ license exams, anything worse than 20/40 requires
additional evaluation; 20/200 in the worse eye is considered legally blind. Low
5See details in http://flywheel.caset.buffalo.edu/wiki/Image:Dcp_2640.jpg.
7The Christie Mirages claim 5000ANSI lumens, which on a 3 m × 3 m screen of
this type, through the active stereo eyewear, yields about 5fL brightness.
accuracies of 1 pixel in 1000. Now that there was brighter
projection, the screen material also had to be chosen carefully
to maximize contrast and minimize internal light spillage on
the other screens (too much of which reduces the contrast of
the images and makes them look washed out).8(None of these
problems occur with normal use of projectors since they are
not typically edge-matched, especially on multiple edges.) This
system also used active stereo at 60 Hz/eye (the projectors update
at 120 Hz) and could, with the SGI Reality Engine, get ∼25
graphic scene updates per second, a 3x improvement over the
For this CAVE, about 60% of the cost was in the SGI 8-processor
shared-memory cluster. This DLP-based CAVE is still built9and
to 1024×1024). The acuity is still roughly 20/140 acuity from the
center of a 3 m CAVE that has ∼1 megapixel/screen.
EVL’s research focus has always been aimed at practitioners
of scientific visualization and artists. While the first and second
generation CAVEs were quite effective in conveying immersion,
the 20/140 visual acuity resulted in ‘‘legally-blind’’ scientific
visualization, admittedly contradiction in terms, but it was state-
of-the-art VR at the time nonetheless. The number of pixels per
the time, so instead EVL research started to focus on tiled displays
with dozens to hundreds of megapixels . By adopting what
we learned from building these tiled displays and the computer
clusters that drive them, we were able to design the StarCAVE,
a third-generation tiled CAVE completed in July 2007 at Calit2 at
the University of California in San Diego; the down-projected floor
was added in May 2008. (See Figs. 1–3) The StarCAVE exploits
tiled visual parallelism to increase visual acuity to ∼20/4010from
3 m away, and brightness to ∼6 foot Lamberts (6fL), through
8We used a ‘‘Disney Black’’ screen, its unofficial name, from Stewart
(http://www.stewartfilm.com/). It has never been clear what the official name is,
but one can ask for it unofficially and get it.
10We used a scanned-in ‘‘illiterate’’ eye chart (the one with the E’s in various
directions) at the proper viewing distance to judge the acuity. We assume the
projectors are at optimal focus. 20/40 was subjectively discernable from 3 m. At
1.5 m from the screen, we discerned 20/60.
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T.A. DeFanti et al. / Future Generation Computer Systems 25 (2009) 169–178
Fig. 2. A photograph of the StarCAVE from the outside showing the entry door
the glasses,11uses LCOS LCD projectors with integrated circular
polarization coupled with passive lightweight circularly polarized
eyewear similar to sunglasses, instead of much heavier battery-
powered active shutter glasses used with second generation
CAVE DLP projectors. The StarCAVE achieves approximately 34
megapixels per eye, fully surround, including the floor (but no
ceiling). The cost is about the same as the first and second
generation CAVEs, except in 2007, the computers were only 10%
of the cost, the projectors 40%, the screens and frames 40% and
the tracking and audio the remaining 10%.12The StarCAVE was
primarily funded by Calit2, and is also supported by the OptIPuter
Also deserving of note is what we describe as a fourth-
generation CAVE, called the VarrierTM,14developed at EVL  and
replicated at Calit2. It is a 40 megapixel per eye autostereo device
(meaning no stereo glasses are worn by the user), and it is made
out of 60 LCD 1600×1200 panels (not projectors). It is also part of
the OptIPuter Project. See also EVL’s work on Dynallax , which
is an outgrowth of Varrier.
11Commercial movie theater screens typically achieve 14fL brightness. Bright-
ness on stereo movie theater screens is not standardized, but ranges from 0.5 to
7fL. The metric equivalent of 1 fL is 3.426 candelas/m2.
12Another 3rd generation CAVE-like system, the C-6, can be seen at Iowa State,
see http://www.public.iastate.edu/~nscentral/news/2007/mar/C6.shtml; It uses 24
Sony SXRD 4K projectors to get 100 megapixels per eye spread out on six screens.
13NSF Cooperative agreement ANI-0225642.
14Varrier is a trademark of the Board of Trustees of the University of Illinois.
2. Design of the StarCAVE
The StarCAVE was designed to be replicable by committed
researchers. In summary form, additional design criterion were:
prime user and several observers
• bright, high-resolution, high-contrast visuals at∼ 20/40 vision
• lifelike, immersive ambient auditory experience, dynamically
scaled to arbitrary virtual scenes, for one or more listeners,
which necessitates a platform to explore and evaluate
– multiple approaches to immersive audio experience, and
– sonification of scientific data in certain visualization contexts
• straightforward acquisition, operation, maintenance, and pos-
sible upgrades with commodity projectors and computers.
Within the following constraints:
• ADA compliance (wheelchair accessibility)
• a low-as-possible ambient noise environment
• seismic safety compliance
• a substantial but not unlimited budget (US$1,000,000)
• non-depolarizing rear and front projector screens.
The StarCAVE is contained in a room that is approximately
9.15 m3, which affected the choice of projectors, projection
distances, screen sizes, cable lengths, and computers.15ADA
compliance was also a consideration that made installing a rear-
projection floor (that is, projecting from the underneath) for us
impossible—there is no practical and safe way to get a wheelchair
onto a raised floor screen 3 m up in the air unless one installs
an elevator, not an option in an existing space.16Therefore, we
decided on a down-projection reflective floor, and rear-projection
horizontal surround screens, and no ceiling, a compromise that
has worked acceptably in the past with earlier CAVEs, and works
even better in the StarCAVE. The floor is painted with marine-
quality polyurethane that has aluminum particles suspended in
it, a commercially available product that, unlike normal front-
projection polarizing screens, can be walked on.
360◦surround VR changes the viewing paradigm so that the
user never needs to horizontally rotate the image as one must
when the screens fail to go all the way around, but one does need
to design a means for entry. We created a door by putting one of
the 5 walls on tracks perpendicular to that wall, which allow it to
slide open and closed (Fig. 3).
Building a CAVE-like display with passive polarization on more
than one screen, instead of using active shutter glasses, presents
challenges perhaps obvious only to a practitioner of projected
virtual reality, mainly due to the complexity of maintaining
polarization with rear projection, in particular. A polarized
projector beam cannot not be folded using mirrors at angles more
than ∼40◦, lest the polarization be lost, an issue because folding
is normally used to minimize the space needed outside a CAVE.17
The rear projection screens need to be polarizing-preserving, not
normally the case with rear-projection screens, and as diffuse (low
gain) as possible to minimize hot-spotting (see Fig. 4). The spec
15We recommend to anyone building a CAVE to get a bigger room. 6-wall CAVE-
like systems in Stockholm, Gifu, Iowa, and Louisiana have used mirrors or had big
enough rooms. Of course, one could request from the architects a 3 m2hole in the
floor and ceiling of a 3-story space, but this is harder done than said, in practice.
16We actually did specify an elevator, and one was provided, but the pathway
to the StarCAVE space was unfortunately blocked by a huge insurmountable steel
beam added during the value engineering phase, not to our knowledge until too
and there needs to be room for the projector body as well. This means a 3 m2CAVE
with normal lensing and unfolded optical paths requires a room ∼18 m on the
diagonal, minimally, with no obstructions. Not having a space that big or the option
of folding the optics, we procured, instead, very wide angle lenses that require only
1x the screen width, and smaller screens.
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T.A. DeFanti et al. / Future Generation Computer Systems 25 (2009) 169–178
Fig. 3. A photograph taken with the camera being tracked of the simulated interior of the Calit2 Building at UCSD. Note the minimal seams, excellent perspective rendering,
and the effect of the floor. Effects of vignetting and off-axis viewing are seen here as well, far more noticeable in still photographs than perceived when experienced live.
Fig. 4. Hotspotting of illumination (left) versus more even dispersion (right) on
polarizing preserving screens with different coatings.
attributes in optimistic qualitative, not quantitative terms; all we
tested failed to meet our requirements of less than 3% ghosting
on center. We worked with a custom screen manufacturer18for
a rigid screen with excellent characteristics as quantitatively
measured and qualitatively perceived. Thus, we use screens that
are 1.2 m by 2.13 m coated PMMA (polymethyl-methacrylate)
rigid plastic, illuminated from the back by JCV HD2K projectors
with 1:1 wide-angle lenses. All the projectors and screens need
to be held in place to sub-pixel precision, so a steel exoskeleton
18The single element rigid grey screen we use is the custom-fabricated rps Visual
Solutions’ ‘‘rps ACP Cinepro Ultra Screen’’. It has a specialized coating on a substrate
acrylic which creates an opaque screen. rps/ACP were extremely generous with
their time and effort in reformulating screen coatings until we were able to achieve
polarization separation of better than 5 stops (∼98%) in the middle and 3.4 stops
ratio of ∼8.5:1 and transmits about 50% of the rear-projected light. We needed to
use rigid screens because the typical flexible membrane screens used in CAVES
billow with air pressure, and in our case, would likely sag on the tilted top and
bottom rows, plus it is not known how to effectively coat a flexible screen with
this polarizing-preserving high-contrast spray coating.
and screen corner details were designed by Calit2’s Greg Dawe,
rpVisual Solutions, Inc. and ADF, Inc. and fabricated by computer-
assisted means. The screens are positioned in 5 columns of 3
panels high, with the top and bottom ones tilted in by 15◦to
maximize the practical on-axis user view of all the projectors19
(see Fig. 5). This required manufacturing and supporting 10
trapezoidal and 5 rectangular screens to very fine mechanical and
structural tolerances (0.1 mm, see Fig. 6), considering the size of
the StarCAVE. As noted above, one of the 5 columns, along with its
6 projectors, 3 screens, and 3 computers, rolls in and out 1.5 m on
tubular steel rails, thus providing access for people to the interior
of the StarCAVE.
The trapezoidal/pentagonal shape, an optimized solution to
fitting in the 9.144 m2physical room, also turns out to have many
advantages over the standard cubic CAVE. Interior light spillage
has been noticeable with cubic CAVEs, especially in variants that
did not use contrast-preserving (dark) screens. Since they form a
pentagon, none of the StarCAVE matte-surfaced screens directly
reflects on any other into the user’s eyes. The 108◦angle between
the screens (instead of 90◦) means less light spillage from screen
to screen, and screen to floor (a 105◦angle). The viewer also
sees somewhat less oblique views in that the typical comfortable
viewing angle is less off-axis than in a standard CAVE because
there are 5 screens20instead of 4. The tilted-in top screens also
mean that the lack of a ceiling screen is not much noticed—one
really has to look uncomfortably straight up to run out of projected
image.21In the Future Research section, we discuss user-centric
ghost and vignette mitigation, which can help improve the stereo
separation and further normalize the illumination in the StarCAVE
and conventional CAVEs.
1915◦was a carefully chosen angle; a few degrees more than 15 would be
more on-axis to the user, but the floor size, as well as the ceiling hole, would be
diminished by the increased angle. The floor-screen height is limited to a two step
rise above the room floor to allow sufficient room for Americans with Disabilities
Act (ADA)-compliant ramps within the room. The alternatives, demolition of the
concrete floor and excavation or the procurement and installation of an ADA
compliant lift and attendant ramps or demolition, were judged too costly.
for standing people.
never been experimentally verified to our knowledge.