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Office of News and Information
Johns Hopkins University
3400 N. Charles Street
Baltimore, Maryland 21218-2692
Phone: (410) 516-7160 / Fax (410) 516-5251

February 25, 1998
MEDIA CONTACT: Phil Sneiderman

The Trick Is in the Triangles
Software gives graphics systems more speed, flexibility

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.

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

Kumar recently posted a preliminary version of the software, called sLIB (short for "surface library"), on the World Wide Web for free downloading by designers who use the Irix operating system. (A Windows version is being developed.) The program is available at:


The secret to Kumar's software, he says, is in how it handles Non-Uniform Rational B-Spline representations, or NURBS, the mathematical shapes that computers can use to depict curved surfaces.

At left 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. Versions at bottom have 5,210 triangles, at left, and 1,750 triangles.

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 re-displayed in a new way. Kumar's software's streamlines this task by generating far fewer triangles and 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.

While Kumar refines sLIB, he is allowing users of computer graphics systems to download the preliminary version at no charge. "This provides us with a wide user base to test the software," he 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."

The Hopkins researcher 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 the level of detail you can see on screen infinitely and still continue to display it at interactive speed," he said. "It may sound impossible, but it's more possible than it seems."

Kumar's research has been funded by the National Science Foundation, the Office of Naval Research and the Department of Defense. He began developing the software 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. This year he won a National Science Foundation CAREER Award, given annually to promising young faculty members.

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