Computing occlusion-free viewpoints

This paper presents methods to compute the locus of all viewpoints from which features on known polyhedral objects can be viewed in their entirety without being occluded by anything in the environment. Convex and concave polyhedra with or without holes and the viewing model of perspective projection are employed in this work. Initially, properties of the occlusion-free and occluded loci of viewpoints are determined. Based on these properties, two methods to construct these loci together with their complexity analysis are presented. In the first method, a boundary representation of the occlusion-free locus is obtained. In the second method, the locus of occluded viewpoints is expressed in terms of a constructive solid geometry representation that consists of a union of component solids. Implementation results and comparison of the two methods are given.