Subodh Kumar Dinesh Manocha Department of Computer Science Department of Computer Science University of North Carolina University of North Carolina Chapel Hill NC 27599 Chapel Hill NC 27599

We present an algorithm for interactive display of trimmed NURBS surfaces. The algorithm converts the NURBS surfaces to Bézier surfaces, tessellates each trimmed Bézier surface into triangles and renders them using the triangle rendering capabilities common in current graphics systems. It makes use of tight bounds for uniform tessellation of Bézier surfaces into cells and traces the trimming curves to compute the trimmed regions of each cell. This is based on trim curve tracing, intersection computation with the cells, and triangulation of the cells. The resulting technique also makes efficient use of spatial and temporal coherence between successive frames for cell computation and triangulation. Polygonization anomalies like cracks and angularities are avoided as well. The algorithm works well in practice and, on the high end graphics systems, is able to display trimmed models described using thousands of Bézier surfaces at interactive frame rates.

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Supported by DARPA ISTO Order No. A410, ONR Contract N00014-94-1-0738, NSF Grant No. MIP-9306208,
Junior Faculty Award, University Research Award, NSF Grant CCR-9319957,
ARPA Contract DABT63-93-C-0048 and NSF/ARPA Science and Technology
Center for Computer Graphics and Scientific Visualization, and NSF Prime
Contract No. 8920219.

Postscript
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