Extracting silhouette curves of NURBS surfaces by tracing silhouette points

Extracting silhouette curves is a key part of hidden curve removal algorithms. It relates directly to the quality of graphics generated by the algorithm, and to the speed and space efficiency of the algorithm. This paper proposes an algorithm for extracting silhouette curves that numerically determines the starting and ending silhouette points, then traces each starting point to obtain the whole silhouette curve. Silhouette loops are obtained by tracing silhouette points on isoparametric lines. This a gorithm is suitable for extracting silhouette curves at any given tolerarce without surface subdivision. The algor ithm is fast and requires minimal storage space.