Scallop hull and its offset

A linear-time algorithm that computes the envelope of the offset of a monotone chain is presented. The scallop hull, an extended notion of the convex hull, of the monotone chain is first computed by using an approach similar to that of the convexhull construction algorithm. The offset of the scallop hull, which yields the desired envelope, can then be computed in linear time from the scallop hull, giving a tool path.