The Johns Hopkins Gazette: March 9, 1998
Mar. 9 1998
VOL. 27, NO. 25


Computer Advance: The Trick Is In The Triangles

Scientist's software gives graphics systems more speed, flexibility

Phil Sneiderman
News and Information

Johns Hopkins Gazette Online Edition

Designers of complex structures--from toasters to nuclear submarines--often use computers to construct three-dimensional models electronically. But a snag can occur: The more detailed these models become, the longer it takes to put them in motion on screen.

Subodh Kumar, assistant professor of computer science, has developed software that addresses this problem by significantly speeding up the way a computer displays a three-dimensional model as it changes position. The program also gives designers greater control over the level of detail that appears on screen.

Subodh Kumar's new software speeds up the way a computer displays a three-dimensional model as it changes positions.

Eventually, Kumar's software could allow users to take a more realistic look around the interior of a building designed on a computer.

"You want to be able to move through this building, to walk through this building," says Kumar, whose research has been funded by the National Science Foundation, the Office of Naval Research and the Department of Defense. "You could put on virtual reality glasses, and they would show you what you're supposed to see on on this side of the room and on that side of the room. That's the tough part: to be able to display so many details in a small amount of time."

Kumar recently posted a preliminary version of the software, called sLIB for surface library, on the Web for free downloading by designers who use the Irix operating system; a Windows version is being developed. Allowing users to download the preliminary version while he refines it "provides us with a wide user base to test the software," Kumar explains. "It's not just a simple surface-rendering system; it's a whole framework in which you can test your own ideas, plug in your own little piece and see how it behaves."

Above are four images of a submarine's torpedo roller produced by sLIB software. The model, courtesy of Electric Boat, was designed using NURBS representation. The top left image is a shaded rendering. The top right version shows its 11,570 triangles. Version at bottom left has 5,210 triangles; the one at right, 1,750 triangles.

The researcher scientist began developing the program at the University of North Carolina, where he earned his doctorate in computer science. Kumar continued working on the project after joining the Hopkins faculty in 1996.

The secret to his software, Kumar says, is in how it handles Non-Uniform Rational B-Spline representations, the mathematical shapes that computers can use to depict curved surfaces. A computer can put NURBS together to form a three-dimensional representation of the complete object.

Kumar's new software speeds up this process when an electronic designer is creating or refining a simple or complex NURBS model.

"This NURBS surface representation is in the computer's memory," explains Kumar. "It's data, just a sequence of bits and bytes that you can keep in a file and send to anybody. But how do you bring it back on screen and manipulate it in three dimensions?"

One common technique is to convert the original model into numerous tiny triangles that, when assembled on the computer screen, look very much like the original shape. Each time the designer clicks a mouse to look at the model from a different point of view, the triangles must be displayed in a new way. Kumar's software streamlines this task by generating far fewer triangles and by taking several other technological shortcuts. These improvements, he says, "enable us to speed up the whole process of displaying the NURBS models by better than 100 to 200 times over the older techniques."

His software also lets a designer zoom in on a particular part of the model to continuously increase the level of detail visible at that location.

Kumar hopes that his software will someday allow a designer to take visitors on a highly detailed "virtual tour" through the interior of a submarine that exists only inside a computer; the computer model could then guide construction of the real vessel. "My dream is to increase infinitely the level of detail you can see on screen and still continue to display it at interactive speed," he says. "It may sound impossible, but it's more possible than it seems."

The sLIB program is available free on the Web at