Two VR systems are currently in use at the VRMedLab. The ImmersaDesk™ and the
R2™, were developed at the Electronic Visualization Laboratory (EVL) here at UIC.
Both systems use CAVElib™ (VR software library developed at EVL) as their C++ VR
systems programming interface (SPI), or library. These VR platforms are derived from the
CAVE™ (CAVE Automatic Virtual Environment), introduced by EVL in 1992. The CAVE,
ImmersaDesk, and R2 are available commercially through Pyramid Systems Inc. The R2 is also
available through SGI through its RealityCenter™ solutions.
A user's head and hand orientation and position are acquired using an Ascension
tracking system with tethered electromagnetic sensors. Stereographics' LCD stereo shutter
glasses are used to separate the alternate fields being projected in user-centered
perspective stereo. This results in slightly different images being seen by each eye and
producing a stereo image for the user or users.
ImmersaDesk™
Developed at EVL in 1994, the ImmersaDesk is a drafting table format VR display. It
features a 67x50-inch rear-projected screen at a 45-degree angle. Up to 5 users wear
shutter glasses to view high resolution, stereoscopic, head tracked images. The
ImmersaDesk screen mostly fills a user's field of view, and at the same time enables the
user to look forward and down. One user's head is tracked, allowing an accurate
perspective to be generated. A tracked wand is also used, so that the user can interact
with the environment. The system is equipped with stereo sound supported by the Vanilla
Sound Server (VSS), sound server software developed at NCSA in Urbana, IL. The ImmersaDesk
cabinet is on wheels and folds up and fits through doors. It can be deployed in offices,
exhibition spaces, galleries or museums.
The ImmersaDesk was developed subsequent to EVL’s CAVE, a 10ft by 10ft by 10ft
rear-projected virtual reality room, as a less expensive and portable alternative to the
CAVE. Both the CAVE and the ImmersaDesk use the same CAVE library software (CAVElib).
Therefore, applications developed for the CAVE can be run on the ImmersaDesk, and vice
versa, without any code changes. Both the ImmersaDesk and R2 (discussed below) use a high
resolution, high bandwidth, short persistence CRT based Electrohome Marquis 8000 or 8500
series projector with projected optics folded by a mirror to increase Compactness. The
projector image is rear-projected onto a high-brightness, diffusing Plexiglas screen.
Standard resolution for both the ImmersaDesk and the R2 is 1280x1024 at 96Hz or 120Hz
stereo.
R2
Previously known as the ImmersaDesk2, the R2 is the most recent VR system from EVL to
become commercially available. According to EVL literature, "The primary design goals
are to accommodate shipment by air and allow "rapid" deployment. The secondary
goal is accessibility…striving for a portable, "one box", user friendly VR
delivery system. Like the ImmersaDesk, the R2 uses a rear-projected drafting-table style
VR system. Unlike the ImmersaDesk, the R2 has hydraulically powered screen-height
adjustments and screen angle adjustments which can change the screen angle from its
traditional 45-degrees to a vertical screen display suitable for large-screen presentation
purposes. The projector is linked to the screen to maintain constant projector/screen
orientation at any screen angle, making re-focusing and re-convergence unnecessary.
Ascension Technology SpacePad® Tracking System
Both the R2 and ImmersaDesk are equipped with this AC electromagnetic tracking system.
The current configuration supports two tethered sensors. One sensor is attached to the
master glasses; the pair worn by the navigator user. The SpacePad supports 6
degrees-of-freedom tracking. This means that the tethered user’s head orientation and
position in three-space is continuously being transmitted to the SpacePad, which in turn
makes this information available to the CAVE application via a CAVE tracker daemon on the
SGI and a CAVE tracker program running on the SpacePad PC. The CAVE library uses this
information to compute and display an off-axis perspective projection of the simulation
that is correct from the point of view and head orientation of the tethered user. The
second SpacePad sensor is attached to a Wand (a kind of 3D mouse with a joystick developed
at EVL). Since the wand is being tracked, it is used as the primary interactive device for
most applications. Like a mouse, it has three buttons which are monitored by the CAVE
library for use as picking and event initiators.
Ascension Technology miniBIRD™ Tracking System
The miniBIRD is a 6 degrees-of-freedom DC tracking system which uses one or more
miniaturized sensors. It lets you accurately track the spatial location of probes,
instruments and other devices. As electromagnetic tracking systems go, it is extremely
accurate. It is currently being used in surgery simulation research.
VR Audio System
The VRMedLab audio system is modeled closely after the EVL portable audio system
configuration. This equipment is used with the R2 and ImmersaDesk to support single-point
and multi-site, collaborative audio in virtual reality applications. The system’s hub
is a Mackie CR-1604 Micro Series mixer which allows multiple inputs and outputs to be
controlled. A Lectrosonic TH-3 Phone Interface which allows the phone lines to go in and
out of the mixer handles telephone communication. The primary user wears a Countryman
Headworn Microphone (Madonna Mic). This microphone is coupled to a Vega T25 Wireless
bodypack which transmits the audio to a Vega R22 UHF Wireless receiver which is connected
to a mixer-input channel. There is also a Crown Ambient Microphone which can pick up audio
from a wide area for a large number of people when individual microphones aren’t
possible. Both Onyx2s have audio inputs and outputs which are also patched into the mixer.
SGI Rack Onyx2™ IR2™
At present, SGI’s highest end graphics/computational platform and also one of the
worlds most advanced graphics machines. The single rack Onyx2 can accommodate up to eight
CPUs, and up to two fully expanded graphics pipes. The VRMedLab rack Onyx2 has one fully
expanded graphics pipe and one two-processor CPU node. It is capable of rendering a
512x512x256 volume of radiological data in real-time (~15 fps). The two Onyx platforms in
the VRMedLab are used to drive the ImmersaDesk and R2. Each computer handles both the
computational and graphics portions of the VR applications being run. UNIX operating
system.
SGI Onyx2 DS IR™
The SGI Deskside Onyx2 is a portable version of the Rack Onyx2. It is about the size of
a small coffee table. It can accommodate one graphics pipe and up to four CPUs. The
VRMedLab Deskside Onyx2 has 2 two-processor CPU nodes and 1 partially expanded graphics
pipe. Since it is so small, compared to the Rack Onyx2, it is ideal for conference duty.
UNIX operating system.
ATM Connections
Both Onyx2s are equipped with Asynchronous Transfer Mode (ATM) cards which connect
these machines to the West Camp OC3 ATM switch. ATM is a Sonnet fiber-optic protocol which
supports quality of service. West Campus is connected to East Campus via an OC12 ATM
backbone. OC12 supports speeds of 622 megabits per second. Through this network our lab
can connect directly via ATM to EVL’s vBNS and StarTap access points.
SGI Indigo2 Maximum Impact
Desktop UNIX workstation with medium end graphics capabilities.
SGI O2
Desktop UNIX workstation with video capabilities.
SGI 320 Visual Workstation
Two Intel™ processor workstations for Windows NT. High-end graphics performance
with a flat-panel monitor.
DELL PCs
