Illustrating the statements of lemmata 3.3. and 3.4. The content of the stack forms a convex chain of edges sorted in increasing order of orientation after each loop. Follows directly from the fact that the stack chain is made of left turns and that it is monotone with respect to the y axis. In this paper we focus on weak external visibility of a polygon. This topic is as yet quite unexplored compared to its internal counterpart.
P is edge visible if for each point x P there exists a ray that supports P at x.
A triangulated graph is a planar graph where every face is a triangle except possibly the outer face. The regions R 1 and R 2 are simple and weakly visible from s. We use the following notation in the algorithm. 2.2 Cluster Analysis One of the most powerful approaches to image segmentation that lends itself to the application of complicated images such as those of outdoor scenes is the method of clustering and this is an area where a great deal of computational geometry can be readily applied.