Output sensitive extraction of silhouettes from polygonal geometry

An algorithm to allow real time interactive extraction and orthographic display of silhouettes of complex two-manifold polygonal object(s) is presented. An off-line pre-processing of all the edges of all polygons enables the efficient extraction of the silhouette edges in real time, once a viewing direction is prescribed. During the interactive session, the time complexity of extracting the silhouette edges is linear in the number of edges in the silhouette, and is typically in the order of O(√n), where n is the number of polygons in the scene. The time complexity of the pre-processing stage is linear in n