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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. DeFanti a,∗ , Gregory Dawe a , Daniel J. Sandin b , Jurgen P. Schulze a , Peter Otto a , Javier Girado c ,
Falko Kuester a , Larry Smarr a , Ramesh Rao a
a
California Institute for Telecommunications and Information Technology (Calit2), University of California San Diego (UCSD), United States
b
Electronic Visualization Laboratory (EVL), University of Illinois at Chicago (UIC), United States
c
Qualcomm, Inc., United States
article
info
Article history:
Received 19 February 2008
Received in revised form
18 July 2008
Accepted 22 July 2008
Available online 17 August 2008
Keywords:
CAVE, Computer-supported collaborative
work
Distributed/network graphics
Graphics processors
Graphics packages
Image displays
Interactive environments
Network communication
Sonification
Teleconferencing
Virtual reality
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 rearprojected 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.
1. Introduction
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 projectionbased surround virtual reality (VR) system, variants of which
have been in development since at least 1991 [1–3]. The first
CAVE1 prototype was built in 1991, showed full scale (3m3 ) in
∗
Corresponding author. Tel.: + 1 312 996 3002; fax: +1 312 413 7585.
E-mail addresses: tdefanti@ucsd.edu, tom@uic.edu (T.A. DeFanti),
gdawe@ucsd.edu (G. Dawe), dan@evl.uic.edu (D.J. Sandin), jschulze@ucsd.edu
(J.P. Schulze), potto@ucsd.edu (P. Otto), jgirado@gmail.com (J. Girado),
fkuester@ucsd.edu (F. Kuester), lsmar@ucsd.edu (L. Smarr), rrao@ucsd.edu
(R. Rao).
1 The name CAVETM was coined by the lead author of this paper for the VR room
being built at at the Electronic Visualization Laboratory (EVL), University of Illinois
0167-739X/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.future.2008.07.015
public at SIGGRAPH’922 and 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’’ [4] 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 m2 screen, 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.
2 Michael Deering of Sun Microsystems, Inc. exhibited a 3-wall similar system
for one user called the Portal at SIGGRAPH’92 [3]. The 3-wall+floor CAVE at
SIGGRAPH’92 allowed multiple users.
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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.3 Besides providingan experience
of ‘‘low vision’’,4 the 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 3D perspective scene per second, insufficient for smooth animation).
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 nonmagnetic 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
SGI Onyx.
A second-generation CAVE was developed by EVL in 2001,6
featuring Christie Mirage DLP 1280 × 1024 projectors that are
7 times brighter7 than 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
3 Calculated 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
odometer/speedometer gauges can’t be read, even when in focus (as everything in a
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 [5].
4 In typical drivers’ license exams, anything worse than 20/40 requires
additional evaluation; 20/200 in the worse eye is considered legally blind. Low
vision is sometimes used to describe visual acuities from 20/70 to 20/200, according
to http://en.wikipedia.org/wiki/Blindness.
5 See details in http://flywheel.caset.buffalo.edu/wiki/Image:Dcp_2640.jpg.
6 See http://www.evl.uic.edu/pape/CAVE/DLP/.
7 The 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
first-generation SGI Crimsons, resulting in much smoother motion.
For this CAVE, about 60% of the cost was in the SGI 8-processor
shared-memory cluster. This DLP-based CAVE is still built9 and
sold, although PCs now run the 1280 × 1024 screens (often cropped
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 stateof-the-art VR at the time nonetheless. The number of pixels per
screen was impractical to improve with the projector technology of
the time, so instead EVL research started to focus on tiled displays
with dozens to hundreds of megapixels [6]. 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 ∼20/4010 from
3 m away, and brightness to ∼6 foot Lamberts (6fL), through
8 We 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.
9 See http://www.fakespace.com/cave.htm.
10 We 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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2. Design of the StarCAVE
The StarCAVE was designed to be replicable by committed
researchers. In summary form, additional design criterion were:
• Fully-tracked VR immersion (360◦ look-around capability) for 1
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 possible upgrades with commodity projectors and computers.
Within the following constraints:
•
•
•
•
•
Fig. 2. A photograph of the StarCAVE from the outside showing the entry door
nearly closed.
the glasses,11 uses LCOS LCD projectors with integrated circular
polarization coupled with passive lightweight circularly polarized
eyewear similar to sunglasses, instead of much heavier batterypowered 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%.12 The StarCAVE was
primarily funded by Calit2, and is also supported by the OptIPuter
Project.13
Also deserving of note is what we describe as a fourthgeneration CAVE, called the VarrierTM ,14 developed at EVL [7] 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 [8], which
is an outgrowth of Varrier.
11 Commercial movie theater screens typically achieve 14fL brightness. Brightness 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 .
12 Another 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.
13 NSF Cooperative agreement ANI-0225642.
14 Varrier is a trademark of the Board of Trustees of the University of Illinois.
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.15 ADA
compliance was also a consideration that made installing a rearprojection 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.16 Therefore, 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 marinequality polyurethane that has aluminum particles suspended in
it, a commercially available product that, unlike normal frontprojection 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
15 We recommend to anyone building a CAVE to get a bigger room. 6-wall CAVElike 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 m2 hole in the
floor and ceiling of a 3-story space, but this is harder done than said, in practice.
16 We 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
late.
17 Normal projector lenses require a throw distance of at least 2x the screen width,
and there needs to be room for the projector body as well. This means a 3 m2 CAVE
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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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.
sheets on available screen materials describe polarizing preserving
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 manufacturer18 for
several months to iteratively develop and test coatings, and created
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
18 The 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
(∼90%) at the screen corner from 1.5 m away. This screen has a remarkable contrast
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 computerassisted 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 m2 physical 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 screens20 instead 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.21 In 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.
19 15◦ 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.
20 6 and 7 screen columns were also considered but wouldn’t fit in the room unless
the screens were shrunk accordingly, which would make 3 of them not high enough
for standing people.
21 6-screen cubic CAVEs, when the entry is tightly closed, have potential air supply
considerations. A CAVE full of people may well quickly up all the oxygen but this has
never been experimentally verified to our knowledge.
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Fig. 5. StarCAVE diagram showing sectional field of view, projector light paths, and screens (measurements in inches).
Fig. 6. Detail showing size of pixels and number of which are blocked by screen
edge supports in (left to right) 1st, 2nd, and 3rd generation CAVEs, in inches.
3. Choice of the StarCAVE projectors
As mentioned above, we chose to use polarized stereo for the
StarCAVE.22 Achieving stereo in any projected VR system typically
absorbs ∼90% of the projector lumens because one needs to
polarize both the projector and the user’s glasses, losing between
3 and 4 stops (88%–94%) of the light. In order to minimize internal
light spillage and maintain contrast, rather dark grey screens are
used in successful CAVEs, which means another stop of light is
typically lost (5 stops is 97%, which means only 3% of the light
gets through to the screen). One method to get enough light is
to use theater-bright (5000–10,000 lumen) projector(s), but these
are ∼$100,000 each, take significant power (2kW for 5000 lumens
and 4kW for 10,000 lumens) and cooling, and they are physically
big and heavy. Fortunately, JVC makes HD2K projectors which
are designed for stereo simulator installations, and which output
cleanly polarized light. By reversing the direction of the circular
polarization with a retarder plate, with near zero loss of light, one
polarizing filter is eliminated, gaining about a stop in brightness.
These 1920 × 1080p projectors are about 1/10th the weight,
cost and power of big theater projectors and accept short throw
wide-angle lenses, which means the throw distance is the same
22 We also investigated color-separation stereo encoding with Infitec [9] filters,
but this technique only works well with xenon lamps which only are found on
theater-class projectors, well out of our price and power budget.
as the screen width, a critical feature, as noted above, for fitting
in a room without folding the projection with mirrors (which,
remember, will de-polarize the light if at an angle >40◦ ). Since
the HD2Ks are projecting on screens that are about 1/4th the size
of classic 3 m2 CAVE screens, another two stops of brightness are
gained, so even with these claimed 800-lumen projectors (which
we measure to be 300 lumens after 100 h of lamp use) the StarCAVE
affords the user 6fL/eye through the circularly polarized eyewear
at 50–1 contrast.23 JVC provided us software to intensity- and
gamma-match the 34 projectors so they are all adjusted to the
same color and brightness (within +/ − 1/5 stop), an intractable
manual task. We did, however, need to manually position and
align the projectors, which took days of work and is not perfect.
(See the Future Research section for thoughts on auto-alignment
techniques.) One feature is that these projectors can be remotely
controlled through their serial ports, which means one does not
need climb scaffolding to manually turn them on and off (which
would really have been manual since we had to tape over the
projector’s remote control receivers because the tracker camera
infrared illuminators were interfering with them!).
4. Choice of StarCAVE computers
Every projector pair for the 15 vertical screens and two halffloor screens is driven by a computer node (specifically, an
Intel quad-core Dell XPS 710 computer using ROCKS [10] and
CentOS [11], with dual Nvidia Quadro 5600 graphics cards). We
use an additional XPS 710 machine as the head node to control
the rendering nodes, for a total of 18 nodes. The nodes are
interconnected with 1 Gigabit Ethernet and 10 Gigabit Myrinet
networks and connected to out-of-room networks with 5 × 10
Gigabit Ethernet. We chose these particular Dells because they
were available with the 1KW power supplies needed to power
the dual 5600 cards and because they have large (∼12 cm) fans
23 Details: readings taken with Minolta F Spotmeter at ISO setting of 100 while
multiple screens displayed 4 × 4 black & white pattern from the center of the
StarCAVE. Projector output at the (projector side) center of the screen: ∼12fL. White
field at the (viewer side) center of the screen: ∼8.5fL (∼1/2 stop loss due to screen).
White (through eyewear) at center screen: 6fL (∼1/2 stop loss due to eyewear).
Black (through eyewear) at center screen: less than 1/10fL, thus >50:1 contrast
ratio. Worst case white through eyewear) off axis from StarCAVE center to a screen
corner: ∼1.3fL, which is 2 stops, a significant amount.
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(unlike rack-mounted PCs) that are relatively quiet. (Low fan noise
is important in any audio-visual environment if quality audio
using speakers is a goal. We could not move the computers to
another room because DVI copper cables for 1920 × 1080p images
are (maximally) about 15 m long; extending the 34 dual-link
DVI signals over fiber to our server room would cost about as
much as the computers themselves, so we carefully listened to the
computers fan noise before we bought them!24 ) We also bought
spares of parts not easily replaceable: one rectangular and one
trapezoidal screen, 2 XPS 710/5600 computers, and four HD2K
projectors which we use for a 2-screen development system in a
VR lab, but which are available for StarCAVE maintenance when
needed. Both the specific computers and projectors we use have
already been discontinued, replaced by newer models, so it is
considered critical for maintenance to have identical spares bought
with the rest and set aside.
5. Tracking
For head and hand tracking we use a wireless, optical tracking
system by ART Tracking [12]. It consists of four infrared cameras
and a Flystick2, a six degree-of-freedom (DOF) device with five
buttons and an analog joystick. We mounted the cameras at the
top of the walls. The ART system communicates via Ethernet with
a VRCO Trackd [13] demon running on the head node of the
rendering system. Trackd provides the application developer with
6 DOF positions for hand and head, as well as the status of all
buttons and the joystick on the joystick. The ART system has an
accuracy of under a millimeter at 60 Hz.
6. Audio for the StarCAVE
Two very significant impediments are encountered when trying
to provide an auditory experience to match the resolution and
immersive quality of the StarCAVE’s visuals:
• The StarCAVE’s virtually seamless, 360-degree rear projection
screen construction precludes the use of laterally placed
loudspeakers which are normally used to enhance spatial
imaging of sound. Lateral speakers would cause shadowing or
block the user’s view of screens.
• The acoustical environment is extremely difficult to control
given the StarCAVE’s extremely acoustically reflective screens
in a symmetrical deployment, devoid of free-field or absorptive
attenuation, which causes unusual modal artifacts (e.g., resonances and cancellations). These considerations shaped all ensuing decisions concerning the physical design of the system.
Much discussion focused on driver element designs and
materials. Ribbon tweeters, planar speakers and thin line arrays
were investigated but rejected as too difficult to mount or control.
Head-tracked, binaural, headphone approaches were identified
and explored as an obvious choice for a single user solution,
and an implementation using new, custom software is under
development. However, headphone-based, head-tracked systems
are unsuitable for multiple simultaneous users who may also
want to be conversing with each other. Since space and therefore
speaker size was limited, a sub-satellite speaker system, as found
in consumer and professional 5.1 systems, was chosen.
We investigated new small speaker enclosures designed
by MeyerSound, Inc. for use in the LCS Constellation active
reverberation enhancement system. These small, wide-range,
wide-dispersion speakers, measuring 10 cm2 , were selected for
24 Noise level of PCs is not something given in manufacturers’ specifications, nor
is this information available on the web.
audio quality, robustness, positional versatility, their integrated
equalization and system controls, and enthusiastic manufacturer
support. It was hypothesized that a combination of direct and
reflected sound from three arrays of 5 speakers would provide
ample coverage for either 5.1 multichannel audio (which matches
well to the 5-sided StarCAVE environment) or up to 15 channels
of discreet audio diffusion. Models of radiation and absorption
patterns were sketched onto design drawings and a plan for exact
speaker placement evolved:
• Cluster 1: 5 MM4 speakers mounted in a tight cluster overhead
with radiation patterns directed at the upper portion of the 5
screens, which would in turn reflect at a lowered angle onto the
ears of the listener.
• Cluster 2: 5 MM4 speakers mounted at the top-corner of each
upper screen, sharing the mounting structure of the infrared
positional tracking emitters, radiating directly.
• Cluster 3: 5 MM4 speakers mounted at the bottom-center of
each lower screen, angularly directed at the ears and exiting
through the open top of the structure
• A subwoofer channel was designed into the flooring structure
of the StarCAVE, with ports in each of the five corners.
15 channels of amplification are provided by QSC Multichannel power amps. Equalization and panning are controlled by 2
Meyer/LCS Matrix 3 units, calibrated by Richard Bugg of MeyerSound. Additional analysis equipment was brought in to help with
system calibration. Extensive equalization was required, as analysis revealed extensive spectral non-linearities, as anticipated (see
Fig. 7).
Run-time electronics and panning was initially handled by a
large MaxMSP [15] patch running ICST Ambisonics [14] and using
two MOTU multichannel interfaces. All source and control, with
the exception of system EQ, has now been integrated into a series
of MaxMSP patches running on a Mac desktop computer. Soundfile
playback is handled here along with tone and noise source testing.
Several approaches to panning and imaging are implemented
including Ambisonics, VBAP [16] and UCSD’s Designer-derived
spatializers [17]. Positional and user input is tracked from a
StarCAVE Linux computer, and communicated to the audio host.
Next, we installed a Yamaha YSP-1100 sound projector, which
uses 40 speakers in a single rectangular enclosure 1, 030 × 194 ×
118 mm in size25 (see Fig. 8). This approach uses a derivative of
wave-field synthesis [18] (WFS) to direct tightly focused ‘‘beams’’
of audio, in order to provide consumers with surround sound
without using rear speakers. The system depends upon bouncing
first reflections off the side walls; in this context the extreme
acoustic reflectivity of the StarCAVE actually worked in our favor.
The Yamaha YSP technology was difficult and time-consuming
to calibrate and several positions were tried before we began to
achieve some degree of convincing surround sound. The YSP device
will only process Dolby or DTS encoded surround audio, which
limits its immediate usefulness without modification or additional
equipment.
The initial MM4 implementation produced reasonably good
results with some sense of immersion and good audio fidelity.
Users noticed that loud levels overloaded the space, resulting in
degraded intelligibility, and a sense of missing lateral energy was
noticed, as was an impression of too much overhead energy. The
imagery was somewhat unstable and lacking in spatial clarity,
which we hypothesize is due to the wide diffusion patterns of the
speakers in a too-reflective environment.
25 See http://www.yamaha.com/yec/ysp1/idx_spec_ysp1100.htm.
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Fig. 7. Full range impulse response of StarCAVE before equalization, showing extreme spectral non-linearities.
Performance of the floor-mounted subwoofer was found to be
sufficient for its intended use, though low frequencies are noticeably localized in the lower part of the structure. An additional overhead subwoofer should alleviate that problem. Listeners respond
favorably to the low-frequency physical sensation of bass transferred through the floor.
Comparison of the performance of the various spatial processing and diffusion approaches is a complex task and the subject of
ongoing study. Testing for subjective and objective data is being
designed.
We found that although difficult and time-consuming to
calibrate, the Yamaha YSP technology provided stable imagery
and a good sense of immersion with somewhat less unintended
overhead directionality than the initial approach. Fidelity was
worse than the Meyer components, but the YSP has a wide variety
of useful calibration features such as beam width and focal length,
wide ranging horizontal and vertical directivity controls, and is
relatively inexpensive. Image control was better than the Meyer
components and the usefulness of the YSP is leading to the design
and implementation of a custom WFS system.
we duplicate critical data on the 500 GB local drives on each PC,
which considerably cuts down on startup time, if warranted. We
are currently experimenting with distribution of data over the 10G
Myrinet connections to each PC, since speed in loading models is
important to users.
Among the new applications we wrote for the StarCAVE in 2007
and early 2008 are:
• The Protein Viewer (Fig. 1): This application connects the
•
7. Software for the StarCAVE
We currently support two software environments to drive
the StarCAVE: OpenCover, which is the OpenSceneGraph-based
VR renderer of COVISE [19], and EVL’s Electro [20]. However,
any software capable of driving a multi-screen and multi-node
environment should be able to run in the StarCAVE (e.g., CAVElib),
as long as it can accommodate the tilt of the upper and lower
displays, as well as handle the pentagonal arrangement of the
walls, both of which are, of course, non-standard configurations
for immersive virtual reality systems. We use ROCKS-based OS
distribution and management to quickly install and recover nodes.
As mentioned before, the projectors are connected via their serial
ports to simplify remote control of all their programmable features,
including on/off.
8. Applications in the StarCAVE
Most of the applications that run in the StarCAVE were
developed over the two years that our prototype 4-projector,
two screen test version existed before the StarCAVE was finished.
Once the StarCAVE’s walls were configured in OpenCOVER [21],
porting the software to the StarCAVE was mostly a matter of
recompiling the source code. Since there are 17 rendering PCs,
•
•
•
StarCAVE to the PDB data bank server [22] to download one
of ∼50,000 protein structures and display it in 3D. We use
PyMOL [23] to convert the PDB files to the VRML format,
which our visualization software can read. The user can
choose between different visualization modes (cartoon, surface,
sticks), load multiple proteins, align proteins, or display the
corresponding amino acid sequence. The high resolution of the
StarCAVE and its surround display capability allows the user to
view a large number of protein structures at once, which the
scientists do to find similarities between proteins.
Bay Bridge: We created an application that displays CAD
models of parts of the new San Francisco Oakland Bay Bridge
in the StarCAVE. This application allows users to walk/fly
through these parts at their real size to find material clashes,
construction errors, and draw conclusions with regards to
constructability.
Neuroscience: We created a virtual replica of the Calit2 building
(Atkinson Hall) to allow users to walk through it in the
StarCAVE. We are currently working with neuroscientists to
find out if the human brain works similarly for wayfinding tasks
in the StarCAVE and in the real world (see Fig. 9.).
OssimPlanet: We integrated the Google Earth-like software
library OssimPlanet [24] with OpenCOVER, allowing us to fly
over the earth with highly detailed satellite images and 3D
terrain. We have used this API in different application domains,
from the visualization of ocean currents to genomics.
Palazzo Vecchio: We visualized a LIDAR scan of the Hall of
the 500 with about 26 million points as a point cloud in
the StarCAVE. Our custom data distribution and rendering
algorithm achieves a rendering rate of about 10 frames per
second.
9. Future work on the StarCAVE
The StarCAVE is a computer science research project as well
as a science, engineering and art production facility. We would,
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is more ghosting as one gets more off axis to the screen and/or
projector. Since full mitigation would consume perhaps 2 stops of
brightness, making the image 4 times dimmer, partial mitigation
at least is worth investigating, especially if it only marginally
degrades real-time performance. Several publications have been
published on this topic, for the general case [27] as well as the
application to passive stereo systems [28]. More research needs to
be done to incorporate angular effects of the glasses (including the
orientation to screen when circular polarization is used, the angle
the glasses are held relative to screen, and the angle the viewing
ray has to the screen).
Fig. 8. Yamaha YSP-1100 sound projector (top), MM4 speaker (middle), and Art
Tracker camera (bottom).
Another area of research is auto-alignment, something that is
well understood in software and available in firmware on high-end
projectors, but would need to be implemented in the Nvidia 5600
GPU for the StarCAVE (given the HD2K projectors), in addition to
the hotspot and ghost mitigation, both of which would also use the
GPUs.
As noted above, the StarCAVE operates at about 20/40 visual
acuity. In order to improve this to 20/20, we would need to
upgrade from 1920 × 1080p projectors to 4K projectors (3840
or 4096 by 2160 or 2400), if their form factor were about the
same. However, 4K projectors are likely to be bigger and cost
∼$100,000 each for a while, and we’d need to buy at least another
15 computers and 30 GPUs, find a projector manufacturer to
internally polarize the red, green, and blue all the same direction
(not normally the case), or switch to Infitec, and we’d need to
provide up to 4x the power and cooling. Doubling the visual acuity
would be a $4,000,000 equipment upgrade at current prices, but
prices fortunately do tend to drop over time.
Fig. 9. Subject in the neuroscience project navigating the Calit2 building, Atkinson
Hall. The stereo was not turned off for this photograph, hence the double image.
for instance, like to build on work by Aditi [25] and incorporate
user locality-based spatial illumination compensation, since we
have accurate 6 DOF information from the tracker. We can mitigate
the vignetting due to projector angle and screen hotspotting by
creating an inverse hotspot that tracks the user and is even
dependent on the particular eye. This technique is possible in
virtual reality environments today by taking advantage of the
programmability of modern graphics hardware. A fragment shader
can be written to take as an input the position of the hotspot and a
brightness falloff value, and then this can be applied to every frame
rendered by the system. In our head-tracked system, the location
of the hot spot needs to be updated for every frame because one’s
head tends to be on the move, even if only slightly. This approach
works only for one viewer, the head-tracked user. In order to
support multiple users, the system would need to be modified to
support multiple head-tracked users, and the display of multiple
stereo image pairs on the screen [26]. In order for the algorithm to
work, empirical measurements with a camera or light meter and
good approximate 3D positions of lenses, screen, and viewer would
be necessary.
In addition, for all but stark black situations, one could subtract
out a small percentage of the other eye’s image to mitigate the
ghosting, again weighted by the user’s tracked position since there
As to future audio work, the StarCAVE head node can output
spatialized sound by sending information about the sound sources
to a Mac G5 computer running a Pd (Pure Data) [29] patch.
Content generation software based in Max and Pd is frequent in
our Calit2 environment, but have yet to be fully adapted to the
StarCAVE systems. Similarly all components needed for convincing
wireless binaural audio have been developed, but integration
and refinement work remains. With the help of industry affiliate
MeyerSound, a small group of dedicated computer music and
engineering students are exploring and developing StarCAVE audio
technologies.26
Acknowledgements
UCSD receives major funding and from the State of California
for the StarCAVE. UCSD receives funding for StarCAVE application
development from the Gordon and Betty Moore Foundation
for CAMERA, the Community Cyberinfrastructure for Advanced
Marine Microbial Ecology Research and Analysis. UIC has received
numerous NSF, DARPA, and DOE awards for virtual reality research
and development from 1992 to the present. Any opinions, findings,
and conclusions or recommendations expressed in this publication
are those of the authors and do not necessarily reflect the views of
the funding agencies and companies.
26 Audio assistance: MeyerSound: Richard Bugg, Steve Ellison, Will Lewis; Barry
Threw, Jann Wissmuller, UCSD: Tom Erbe, Jann Wissmuller, Grace Leslie, Suketu
Kamdar, Kevin Larke, Kyle Knickerbocker, Toshiro Yamada, Michelle Daniels and
Chris Schlyer.
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Thomas A. DeFanti, Ph.D., at the University of California,
San Diego, is a research scientist at the California Institute
for Telecommunications and Information Technology
(Calit2). At the University of Illinois at Chicago, DeFanti
is director of the Electronic Visualization Laboratory
(EVL), and a distinguished professor emeritus in the
department of Computer Science. He has researched
computer graphics since the early 1970s. His credits
include: use of EVL hardware and software for the
computer animation produced for the 1977 ‘‘Star Wars’’
movie; contributor and co-editor of the 1987 NSFsponsored report ‘‘Visualization in Scientific Computing;’’ recipient of the 1988
ACM Outstanding Contribution Award; he became an ACM Fellow in 1994.
177
Gregory Dawe, MFA, is a Principal Development Engineer
at the California Institute for Telecommunications and
Information Technology (Calit2). Prior, at the University of
Illinois at Chicago, Dawe was Manager of System Services
at the Electronic Visualization Laboratory (EVL). He holds
a B.A in Design from the University of Illinois at Chicago
and a MFA from the School of the Art Institute, Chicago.
Daniel J. Sandin is director emeritus of the Electronic
Visualization Lab (EVL) and a professor emeritus in the
School of Art and Design at the University of Illinois at
Chicago (UIC). Currently Sandin is a researcher at EVL at
UIC and at CALIT2 part of the University of California at
San Diego. Sandin’s latest VR display system is Varrier,
a large scale, very high resolution head tracked barrierstrip autostereoscopic display system that produces a VR
immersive experience without requiring the user to wear
any glasses. In its largest form it is a semi-cylindrical array
of 60 LCD panels.
Jurgen P. Schulze, Ph.D., is a Project Scientist at the California Institute for Telecommunications and Information
Technology in San Diego, California. His research interests
include scientific visualization in virtual environments,
human-computer interaction, real-time volume rendering, and graphics algorithms on programmable graphics
hardware. He holds an MS from the University of Massachusetts and a Ph.D. from the University of Stuttgart,
Germany.
Peter Otto has served on the faculties of Cal Arts and SUNY
Buffalo, and as Director of Music Technology at Istituto
Tempo Reale, Florence. He is currently on the faculty of
UC San Diego’s Department of Music as Director of Music
Technology where he played a key role in the development
of UCSD’s Interdisciplinary Computing and the Arts Major
(ICAM).. In January 2008 Otto was named Director of Sonic
Arts Research and Development at UCSD’s CalIT2. Peter
Otto holds a Master’s Degree in composition from the
California Institute of the Arts.
Javier Girado, Ph.D., is a Staff Engineer at Qualcomm
(Graphics team). He earned his M.S degree from the
Buenos Aires Institute of Technology (ITBA), held a
research fellowship at the Industrial Technology National
Institute (INTI), Argentina. He taught at the National
Technology University (UTN) and the ITBA. He completed
his Ph.D. from the University of Illinois at Chicago
(UIC) in 2004. He worked as a Postdoctoral Researcher
at the California Institute for Telecommunications and
Information Technology (Calit2), University of San Diego,
California until 2007. His research interests include virtual
realty (VR), auto-stereoscopic displays, computer vision, and neural networks. He
specializes in camera-based face detection and recognition to support real-time
tracking systems for VR environments, and video conferencing over high-speed
networks.
Falko Kuester, is the Calit2 Professor for Visualization
and Virtual Reality and an Associate Professor in the
Department of Structural Engineering at the Jacobs School
of Engineering at UCSD. He received his MS degree
in Mechanical Engineering in 1994 and MS degree
in Computer Science and Engineering in 1995 from
the University of Michigan, Ann Arbor, and the Ph.D.
from the University of California, Davis, in 2001. His
research is aimed at creating intuitive, collaborative digital
workspaces, providing engineers and scientists with a
means to intuitively explore and analyze complex, higherdimensional data. In support of this research, he is developing new methods
for the acquisition, compression, streaming, synchronization and visualization of
data, including the ultra-high resolution HIPerWall and HIPerSpace visualization
environments.
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Larry Smarr is the founding director of the California Institute for Telecommunications and Information
Technology and Harry E. Gruber professor in the Jacobs
School’s Department of Computer Science and Engineering at UCSD. Smarr received his Ph.D. from the University of Texas at Austin and conducted observational,
theoretical, and computational-based astrophysical sciences research for fifteen years before becoming the
founding director of the National Center for Supercomputing Applications (1985) and the National Computational
Science Alliance (1997),. He is a member of the National
Academy of Engineering and a Fellow of the American Physical Society and the
American Academy of Arts and Sciences. Smarr is Principal Investigator on the NSF
OptIPuter LambdaGrid project and is Co-PI on the NSF LOOKING ocean observatory
prototype.
Ramesh Rao received his MS degree in 1982 and Ph.D.
degree in 1984, both at the University of Maryland,
College Park. Since then he has been on the faculty of
the department of Electrical and Computer Engineering
at the University of California, San Diego, where he is
currently Professor and Director of the San Diego Division
of the California Institute of Telecommunications and
Information Technology and Qualcomm Endowed Chair
in Telecommunications and Information Technology. His
research interests include architectures, protocols and
performance analysis of computer and communication
networks. He was the Editor of the IEEE Transactions on Communications and was a
member of the Editorial Board of the ACM/Baltzer Wireless Network Journal as well
as IEEE Network magazine. He has been twice elected to serve on the Information
Theory Society Board of Governors (’97 to ’99 and ’00 to ’02).