3D Simulation To The Max
Immersive virtual reality enables a broad range of researchers to overcome challenges posed by space constraints, scale, or time variances.
CHALLENGE: Update a six-sided virtual reality system to meet today's needs and lead it into the next generation.
SOLUTION: Design a system that employs the highest resolution projectors available and one of the world's largest graphics computer clusters.
Viewers experience a 100 million pixel virtual cell simulation, partially funded by National Science Foundation grants, in the C6, located at Iowa State University's Virtual Reality Applications Center.
Immersive virtual relaity enables a broad range of researchers to overcome challenges posed by space constraints, scale, or time variances. Biologists use it to shrink themselves down to the cellular level. Manufacturers apply it to developing new products and managing business models. The military employs it to train for real-world combat.
At Iowa State University in Ames, Iowa, the Virtual Reality Applications Center (VRAC) is at the forefront of virtual reality technology. In 2000, VRAC opened the C6, the first six-sided immersive virtual reality system in North America. A new variation CAVE design (Cave Automatic Virtual Environment, see sidebar), the C6 is a 10-foot-by-10-foot-by-10-foot room in which computer images are rear projected on soft vinyl screens supplied by Stewart Filmscreen on all four walls and the ceiling. A single 2,000-pound, 2 ¾-inch thick piece of optically-correct acrylic allows images from the bottom projector to appear on the floor. One of the wall screens is mounted on a pneumatically actuated frame to allow for access to the C6.
Likening the 3D virtual reality experience to a very sophisticated version of a child's Fisher Price ViewMaster, in which the circular disk shows one image for the right eye and another for the left, Dr. James Oliver, director of VRAC, says the brain fuses those images together to make them appear three dimensional. “You don't see the edges of the boundaries; the walls just melt away, and objects come at you from outside or go out to infinity, he says. However, this vision is difficult to convey in a photograph or video because it becomes only two-dimensional. “Without the stereo effect, it looks like a big box with lights on the walls,” he adds.
A diagram of the C6 structure, showing the framework and image overlap requirements.
For its first five years, VRAC's C6 was one of most widely used virtual reality systems in the world. But by 2005, Oliver says that every performance dimension of the C6 needed improvement. “It had some unique innovations in its day,” he says. “But five years is a long time in technology.”
Securing nearly $5 million in funding from the U.S. Air Force Research Laboratory to upgrade the C6, VRAC set out to solicit bids for the project in mid-2005. VRAC received five bids for the project and selected Fakespace Systems, the display system integration division of Marshalltown, Iowa–based Mechdyne Corp., as the installer for the C6 updates in January 2006. Mechdyne was the original installer on the C6 project in 2000. Updates on the system began in May 2006.
In its detailed functional specifications, VRAC required that the new solution be capable of producing a minimum of 4 megapixels at a resolution of 2000 x 2000 per wall for a density of 16.67 pixels per inch. Knowing that increased resolution was high on the list of priorities, Kurt Hoffmeister, vice president of engineering for Mechdyne, says his company wanted to offer VRAC a solution that far exceeded this minimum requirement.
The C6 computer cluster is made up of 49 HP workstations; 48 provide two graphics outputs and one serves as the master node.
Fakespace incorporated 24 SRX-S105 SXRD projectors, manufactured by Sony Electronics, in the update. Introduced in July 2006, the SRX-S105 ultra high-resolution projector — one of four units in Sony's SXRD projector series — was specifically designed for large-venue and high-resolution applications. The 4096 x 2160 resolution of this projector is four times greater than the highest definition television currently available to consumers. On the 10-foot-by-10-foot walls of the C6, pixel density is greater than 34 pixels per inch, and with a total 24 projectors, the system achieves a 100 million pixel stereoscopic display, which is 16 times greater than C6's original display. Of the initial $5 million bid, the facility and technology upgrade — including projectors, electronics, and optics — made up more than $3.5 million of the cost.
Fakespace knew that the only way to meet VRAC's resolution requirement and support stereoscopic viewing with the current technology available was to provide multiple projectors per wall. Four projectors were stacked vertically for each surface, reaching about 10 feet high. “Two blend together to make up a 4096 x 4096 right eye image, and because it is stereoscopic, the other two projectors are providing the left eye image,” Hoffmeister says. “Because the projectors have to overlap each other to produce a square image, we're using Fakespace's own version of optical blending.”
Driving the C6 is a 96-channel workstation cluster — four separate graphic inputs for each projector — that was configured and installed by VRCO, the software division of Mechdyne. According to Matt Szymanski, vice president of VRCO, the cluster is comprised of 48 separate HP xw9300 workstations, each with two graphics outputs, plus an additional workstation to serve as a master node that houses the application and interaction software.
“Each workstation is responsible for generating an image for one-eighth of a given wall,” Szymanski says. “Each video signal coming from a PC is at the slightly greater than HD resolution of 2048 x 1080. Therefore, each wall is comprised of eight PCs generating two contiguous images —one for the left eye and one for the right eye — of 4096 x 4096 resolution, or more than 16 million pixels per side of the C6.”
Viewer Tracking and Sound
Providing the sound for the C6 is a custom, eight-channel audio system. Components include an M-Audio Delta 1010 computer multi-channel audio interface; Peavey MediaMatrix X-Frame 88 audio DSP mixer/processor and MM-8802 audio mixer/processor interface, and A/A-8P audio pre-amplifier; five Extron BUC102 audio balanced-unbalanced converters, and one pair of JBL Control 25AV loudspeakers. Existing audio equipment carried over from the original C6 design include two ATI1604 four-channel power amplifiers, three pairs of M&K S-85TV speakers, an M&K MX-5000 MK II THX subwoofer, and an Audio Technologies BU400 balanced-unbalanced converter.
“I guess you would describe it as 8.1,” Hoffmeister says. “Basically, there are eight channels of sound plus a sub. There is essentially a speaker in each corner, so the four upper corners and four lower corners have a speaker and can generate some directional sound when you're inside the cube.”
A critical portion of the C6 is the viewer tracking system, which links the computer visualizations to the viewer's point of view. “Where they're standing and where they are looking affects what is drawn,” Hoffmeister says. To enhance the viewer's experience, Fakespace incorporated inertial-acoustic IS900 tracking equipment from InterSense of Bedford, Mass. The viewer wears two or three sensors — one for the head and one or two for the hands — and built into the display are a series of small emitters that put out a signal that the tracker picks up on. From there, the computer application knows the person's location inside the C6. “What makes the whole experience so immersive and interactive is that the graphics are being drawn for your head position and point of view, and then with your hand position tracking, there's a certain amount of interaction as well,” Hoffmeister says.
Tweaking the Design
One of the C6's most innovative features — the projector stack — was also one of its greatest design challenges. “Where before we just had one projector for each surface, now we have four of them,” Hoffmeister says. The real installation challenge came with the floor and ceiling. On a catwalk above the system, the projectors are reflected off mirrors to illuminate the ceiling, and the same goes for the floor. “Just mounting that much additional equipment became a challenge,” he says. “Each projector weighs a little over 240 pounds, and there were a variety of safety issues with lifting and mounting that equipment overhead.”
Adding a substantial number of projectors increased the C6's brightness, but also led to heating/air conditioning and electrical challenges. While ventilation for the machine room housing the computers was specified in the design, the projectors also were emitting a significant level of heat, Oliver says, which was initially overlooked in the design plan. “We worked with our facilities people to add more HVAC in the C6 enclosure itself,” he says, which added an additional expense and delayed the construction schedule.
Katie Parrish is a technical writer based in Independence, Mo. She can be reached at firstname.lastname@example.org.