The Trick Is In The Triangles: Speeding Up 3-D Computer Models

A Johns Hopkins University computer scientist has developedsoftware that addresses this problem by significantly speeding upthe way a computer re-displays a three-dimensional model as itchanges position. The program, devised by Subodh Kumar, assistantprofessor of computer science, also gives designers greatercontrol 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 Webfor free downloading by designers who use the Irix operatingsystem. (A Windows version is being developed.) The program isavailable at:

http://www.cs.jhu.edu/~subodh/research/software.html

The secret to Kumar's software, he says, is in how it handlesNon-Uniform Rational B-Spline representations, or NURBS, themathematical shapes that computers can use to depict curvedsurfaces.

A computer can put NURBS together to form a three-dimensionalrepresentation of the complete object. Kumar's new softwarespeeds up this process when an electronic designer is creating orrefining 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 bytesthat you can keep in a file and send to anybody. But how do youbring it back on screen and manipulate it in three dimensions?"

One common technique is to convert the original model intonumerous tiny triangles that, when assembled on the computerscreen, look very much like the original shape. Each time thedesigner clicks a mouse to look at the model from a differentpoint of view, the triangles must be re-displayed in a new way.Kumar's software's streamlines this task by generating far fewertriangles and taking several other technological shortcuts. Theseimprovements, he says, "enable us to speed up the whole processof displaying the NURBS models by better than 100 to 200 timesover the older techniques."

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

While Kumar refines sLIB, he is allowing users of computergraphics systems to download the preliminary version at nocharge. "This provides us with a wide user base to test thesoftware," he explains. "It's not just a simple surface-renderingsystem. It's a whole framework in which you can test your ownideas, plug in your own little piece and see how it behaves."

The Hopkins researcher hopes that his software will someday allowa designer to take visitors on a highly detai