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592 VIRTUALREALITY ON THEINTERNET:COLLABORATIVEVIRTUALREALITYFigure 1: The CAVE and ImmersaDesk. (Left) A person in the CAVE wearing tracked shutter glasses to see the virtual world in
stereo and carrying the wand. (Right) A user sitting in front of the ImmersaDesk wearing the same tracked glasses and carrying
the same wand as in the CAVE. The CAVE and ImmersaDesk users can interact with the same virtual worlds from different pers-
pectives.CAVEs have four walls, a ceiling, and a floor to completely
surround the viewers. This larger space allows five people
to comfortably view the virtual world together, although
again only one person is head tracked (Figure 1).
Another approach is to take multiple screens and, in-
stead of wrapping them around the user, use them to give
the viewer a higher resolution wall made up of several
screens. A single screen, whether in a fish-tank virtual
reality setup or a CAVE, typically has a resolution of 1280
pixels by 1024 pixels. By combining several screens to-
gether, much higher resolutions are possible.
There are many different ways of interacting with the
virtual world and many different devices to allow that in-
teraction. The user may want to navigate a large space
with a joystick or use a set of buttons to change the proper-
ties of the virtual world. Just as the user’s head is tracked,
other parts of the user’s body can be tracked, so the user’s
body can itself be the interface. It’s typical to track the
user’s hand, or the controller the user is holding, to allow
the computer to see where the user is pointing.
Although visuals are the most obvious element of
virtual reality, audio is also important, to give the users
additional feedback. Haptics, the feeling of touch, is also
important in certain virtual reality applications. Often a
lack of feedback to one sense is compensated for by feed-
back to another sense. For example, if you don’t have hap-
tic feedback, you may get visual or audible feedback.
In order to keep up the illusion, the imagery of the vir-
tual world must be drawn at a rate of at least 15 frames
per second per eye. Otherwise, the world will seem to stut-
ter. In a movie theatre, we watch films composed of still
images moving at 24 frames per second and see smooth
motion; it’s the same in virtual reality. This is why vir-
tual reality requires very powerful computers and graph-
ics cards.
Throughout the 1990s, this required very expensive
computers, but now it is possible to do single-screen vir-
tual reality using high-end personal computers. There is
also current research going on in autostereoscopic dis-
plays, where the user will not need to use special glasses
to see computer-generated stereo imagery. For a morethorough discussion of virtual reality, see Sherman and
Craig (2002).COLLABORATIVE VIRTUAL REALITY
In the 1990s, more and more groups around the world
gained access to virtual reality equipment, making col-
laborative virtual reality possible. Again, there are sev-
eral definitions of collaborative virtual reality—every day
many people play collaborative or competitive games on
the Internet, which can be considered collaborative virtual
reality, and sometimes share environments with hundreds
of other players. Since the 1970s, text-based multiuser vir-
tual worlds such as MUDS and MOOS have been popular,
evolving from their origins as collaborative adventure
games and allowing people to communicate and interact
over very-low-bandwidth connections. In the mid-1990s,
with advances in both computing power and network
speeds, users could explore 3D worlds over the Inter-
net through VRML (virtual reality modeling language)
browsers.
For our purposes, collaborative virtual reality requires
connecting up the devices described in the previous
section, allowing people in several places to share a 3D
environment. Some research groups focus on support-
ing existing low-bandwidth Internet infrastructures or
massive connectivity involving thousands of participants
at the same time, as in military simulations or Internet-
based computer games (Singhal & Zyda, 1999) Our
focus on the use of virtual reality for manufacturing, for
scientific purposes, and for information visualization has
a different set of requirements. We are building systems
for small working groups, typically no more than seven
collaborators at a time but with large data distribution
requirements, to share high-fidelity audio and video
communications and large engineering and scientific
data stores over high-speed national and international
networks.
We want to provide high-quality interaction between
small groups of participants involved in design, train-
ing, education, scientific visualization, or computational