Demonstrated by Greg Favalora, cofounder and chief technology officer of Actuality (Reading, Mass.), the 3-D display dome relies on a basic concept that has been around since the late 1950s: projecting pictures rapidly onto a rotating screen.

It was clear that the 117-million-voxel 3-D display demonstrated by four-year-old Actuality is not yet ready for prime time, but it's close.

The rotating-screen approach, when done effectively, causes a viewer's brain to fuse the pictures to create an image "that appears to hover in three-dimensional space," explained Favalora, "enabling users to move around the display and view the image from any angle across a full 360 degrees." But what's been missing, he said, has been "efficient algorithms" to create high-resolution images.

At the heart of the Actuality display is a powerful graphics processing subsystem that maps image data into a 3-D space. It combines a Texas Instruments Inc. C6X DSP with a set of FPGAs that contain the company's advanced rendering algorithms, as well as what Favalora called voxel routers. "These let us shuffle around the bits very fast and do operations on individual voxels very quickly with a sort of rear-modify-write capability," he said. "We can do ANDing, ORing, exclusive ORing and masking operations automatically."

The graphics subsystem not only calculates the voxels that will be projected onto the spinning screen, which receives about 4,000 pictures/second, but it also applies sophisticated processing to pick up some jobs formerly requiring mechanical or optical parts. "We use software instead of mirrors and lenses," Favalora said. The system has a large, high-speed memory system and a graphics pipeline running at over 1 Gbyte/s.

Favalora has been working on 3-D displays since 1988. His work has garnered a National Inventors' Hall of Fame collegiate inventors award, as well as an MIT entrepreneurship competition award for "optical, electrical and software engineering."

Jointly founded by Favalora and 3-D display designer Michael Giovinco in a Cambridge, Mass., basement, Actuality now boasts a staff of seven. Favalora praised "two EEs who did all the electronics work" on the prototype: senior systems engineer Deidre Hall and senior electrical engineer Michael Richmond.

Favalora stressed that the SID demo was "a sneak preview of prototype No. 0.1 as we were finishing it up. We still have some bugs to work out." The prototype makes use of a 600-rpm screen and a projection engine mounted beneath the dome, which is based on a Texas Instruments digital micromirror device.

Actuality demonstrated eight-color images "floating" in a 10-inch-diameter volume. These included a molecular model and a computed tomography scan of a human skull, the latter taken "from a standard medical research database," Favalora said. "Thanks to Open GL, we can use a whole bunch of off-the-shelf software packages, and users don't really have to learn anything new to get 3-D."

The 3-D images demonstrated, which were nice and bright, were defined in the graphics subsystem as "a stack of flat 2-D slices arranged around a center line, like the sections of an apple around its core," Favalora said. The prototype's 117 million voxels are formatted as 198 slices of 768 x 768-pixel images. The system is capable of generating "hundreds" of colors at lower resolution, he noted.

As for remaining bugs, the prototype's displayed images wobbled and the mechanical system was pretty noisy. "We think the problem's with the bearing we're using," Favalora said, "and we're doing a lot of work minimizing air resistance." Several electromechanical problems are now being solved, he said, by changing over from certain off-the-shelf components to customized parts, "and there's an optical pickup we're tweaking."

Actuality is now busy lining up beta partners while it puts "the finishing touches" on the system, Favalora said. "We're now finishing the real-time computer interface, the SCSI interface and the user interface. We want to make sure that users can navigate their 3-D data just as intuitively as they did in 2-D."

Beta shipments will kick off in the fourth quarter. Commercial shipments are expected in 2002.