Deep vision: when walls become doors into virtual worlds.

It was when he was being measured for a new suit that Thomas A. DeFanti, a computer scientist and photographer at the University of Illinois in Chicago, came up with a new angle on virtual reality. DeFanti recalls looking at himself in the tailor's three-mirror booth and wondering whether he could combine computers and a projection system into a high-tech imaging system that would recreate a three-dimensional likeness that would look right from any viewing angle.

Back then in 1991, the only way to create the illusion of being immersed in a computer-generated world was to don a helmet outfitted with tiny computer monitors that fit directly over your eyes.

A few months later, DeFanti, Daniel Sandin, also of the University of Illinois, and some of their colleagues had turned the concept into something they called the CAVE, which stands for Cave Automatic Virtual Environment--a cubic room of screens onto which rear-screen projectors throw computer-generated views of a virtual scene.

A visitor to a CAVE sees--and, these days, sometimes hears, feels, and even smells--a three-dimensional world that seems to engulf him or her. That virtual world can include anything a computer can simulate, from the inside of an atom to an ancient Greek temple or the heart of the Milky Way. What's more, the CAVE dweller can move around the objects and experience them from all sides, just as he or she might in the real world.

Today, 11 years after DeFanti's tailor-shop revelation, CAVEs and wall- or desk-size displays using the same technology are proliferating at universities, businesses, and military and government sites (SN: 2/27/99, p. 136). Scientists use them to analyze data in new ways. Engineers use them to design new products with less reliance on physical prototypes. And many others, including artists, architects, and game designers, are using the systems to devise and display their creations. In short, CAVEs are coming out of the closet.

Most recently, an offshoot of CAVE technology has brought virtual reality to a much wider audience. Show goers at major planetariums and science centers have begun experiencing the sensations of flying through space or other virtual scenes rather than just looking at them. More and more of these entertainment productions embody the scientific simulations once confined to laboratories. Meanwhile, scientists working at these centers are also using the new facilities, after hours, as giant CAVE-like displays for their own research projects.

ROOM WITH YOUR VIEW With traditional visual media, from paintings to photographs to television sets, viewers can't opt for different viewing angles or perspectives. In CAVEs, they can.

To help keep the changing perspectives realistic, a CAVE user wears an eyeglass frame fitted with an electromagnetic or ultrasonic tracking device. It enables the computer to monitor the orientation of the person's head and eyes and redraw images in corresponding perspectives. If several people use a CAVE simultaneously, only the one with the tracker gets the full effect.

In addition to simulating various virtual perspectives, the computers behind some CAVEs can create an illusion of stereovision (SN: 11/12/94, p. 319). In real life, each eye sees a slightly different view of the world. The differences between those views enable our brains to construct 3-D portraits of objects.

To create that 3-D effect in a CAVE, each projector cycles through alternating images of right- and left-eye views at, typically, 60 repetitions per second of each. The CAVE user's eyeglasses are equipped with shutters or polarizing filters that make sure each eye sees only its intended view. The brain then melds those images into a single stereoscopic view (SN: 9/18/99, p. 184).

SUBMERGED IN DATA In a CAVE at the University of Maryland in College Park, an image of a tube with a propeller at one end floats in space. The propeller turns lazily as the cylindrical shell expands and contracts in full 3-D, as if it were breathing.

This particular simulation is designed for probing the vibrations of a torpedo's casing as the weapon travels through the water. The goal of this Navy-funded work is to find ways to dampen the vibrations and thereby make the weapons stealthier, says Amr M. Baz, a mechanical engineering professor and leader of the project.

With a few manipulations of a wand, graduate student Wael Akl zooms in on the torpedo until the view shifts from the outside to the inside of the cylinder. For Akl and the other two people in the CAVE, the cylinder appears to undulate, out then in, all around them. With more wand action, Akl installs different sets of virtual reinforcing rings into the shell so the group can observe how the rings affect the vibration pattern.

This CAVE provides more than just visual simulations of the device's behavior. Ten speakers broadcast sounds calculated to match what the vibrating torpedo casing would transmit into its surroundings. A researcher also can slip on a so-called haptic device, in this case a glove with which one person can "touch" the casing at different locations and feel its vibrations.

For these types of engineering studies, CAVE technology can save time and money by enabling designers to test their ideas before actually building anything. Today, every major car company and some airplane builders do vehicle design using CAVEs or less-elaborate systems that run on single walls or even a tabletop, says Jeff Brum, a product manager at Fake-Space Systems in Kitchener, Ont.

Many oil and gas companies are using such systems to create images of underground formations from existing seismic data. The 3-D projections help analysts locate fault lines and other features that provide clues to good drilling locations.

Some investigators are proving that some of the grandest CAVE-like displays can include whole audiences sitting in theater chairs. In one, people lean back and zoom through a 3-D representation of 100,000 stars derived from actual satellite-telescope data or see dramatic, simulated astronomical events.

After the show, however, the same theater has proven valuable for scientific research. Astrophysicist Michael M. Shara of the American Museum of Natural History in New York describes the museum's Hayden Planetarium as "the CAVE gone wild."

Some evenings, after the planetarium's virtual-reality shows have ended, he and Jarrod R. Hurley, also of the museum, have used the dome to project their computer simulations of dense clouds of stars known as globular clusters. The dome's enormity enables the astrophysicists to simultaneously view stars that are nearby one another yet quite distant from others, all the while maintaining proper scale, Shara explains.

With this unique tool of scientific visualization, Hurley and Shara have found evidence that stars in globular clusters come together and then break apart again into small groups far more frequently than previously thought.

Most theories of stellar evolution portray stars as lone entities or perhaps in a pair with one other star. The newly recognized "promiscuous" behavior, as Hurley and Shara have described it, allows for all kinds of unexpected swapping of stellar gases and other interactions that may dramatically change the life histories of as many as 70 percent of the stars in a cluster. "Things not explainable by conventional stellar evolution became crystal clear," Shara says. He and Hurley describe their ideas about stellar promiscuity in the May 1 Astrophysical Journal.

Before exploiting the planetarium as a CAVE-like display for research, the scientists had been running their simulations on ordinary computer monitors without fully realizing what they were seeing. In the dome, however, "there was a set of these `eureka' moments when you look up on the dome and you say, `Oh, geez. That's what's happening!'" Shara recalls.

NEVER STATIC Three years after inventing the CAVE, DeFanti, Sandin, and their colleagues had also developed a compact version dubbed the Immersadesk. The device is a table-like workstation that a user, wearing stereo glasses, stands in front of. By 1995, Fake-Space had begun manufacturing CAVEs and related products for the commercial market. Today, several other manufacturers are also building CAVE-style displays. The family of devices has grown to include large, single-panel walls and modular CAVEs that can be readily broken down and reassembled for trade shows and other traveling exhibits. And CAVE technology continues to evolve.

Last year, manufacturers introduced digital projectors based on microchips covered with millions of tiny, moving mirrors. DeFanti says the new projectors deliver images in CAVES seven times as bright as their predecessors, which are like ones in projection televisions. "Finally, the CAVE does not feel like it's in moonlight," he declares.

DeFanti and other virtual-reality researchers are also developing CAVE-like systems that use computer monitors rather than projectors. By eliminating distances between projectors and screens, monitors might make CAVE-like displays possible in a fraction of the space of current systems. Theoretically, each cubicle in an office could have its own CAVE, DeFanti speculates.

Researchers are also trying to make CAVE-like displays better for group experiences. To foster collaborative use for such applications as virtual travel, architectural tours, and training sessions, researchers at the Fraunhofer Institute for Media Communication in Sankt Augustin, Germany, unveiled in March a new booth called i-CONE. With its curved, high-resolution projection screen, I-cone allows up to a dozen people to simultaneously view undistorted scenes, claims Martin Gobel of the institute.

Some attempts to push the technology further have failed. For example, Gobel recalls that 3 years ago, the Fraunhofer Institute outfitted a display with odors, but no one noticed them unless they were danger signals, such as the smell of smoke. "It was disappointing that people couldn't smell what we were injecting," he says.

In a new and growing trend, the users of CAVEs and CAVE-like systems are networking them together. For instance, to create the visual sequences used in the current Hayden Planetarium show--"The Search for Life: Are We Alone?" which opened March 2--producers were able to connect the dome via the new high-speed academic network, Internet 2, to a CAVE at the National Center for Supercomputing Applications (NCSA) in Urbana-Champaign, Ill. NCSA's greater computing power and specialized software enabled the producers to run elaborate astrophysical simulations and to transfer excerpts from those simulations to New York for the show.

Despite their different equipment, in one after-hours work session, the two far-flung teams simultaneously inhabited the same scene and consulted about how to manipulate it.

"We both got into the same space, although we were 1,000 miles apart," says Carter Emmart, visualization director at the Hayden Planetarium.

Other networked users are sharing data, touring each other's virtual environments, or staging cyber-art exhibits. Whether stand-alone or networked, room-shaped or domed, CAVE-like displays are becoming portals to anywhere you can imagine.