Image Retrieval using Canonical Cyclic String Representation of Polygons

In image retrieval applications one of the boundary-dependent approaches is matching contours with their polygonal representation. We introduce (1) a new polygonal shape representation, (2) an efficient algorithm to compute a unique representation of a polygon to handle orientation and (3) a matching method that is invariant to rigid and affine transformation. In the method, polygons are represented by a sequence of distance vectors ordered in a predefined cyclic way. Each vector is composed of two primitives which are radial distance from the centroid to a vertex and the following edge distance in a specified direction. Matching of polygons is achieved by bitwise comparison of their string code. The algorithm has a computational complexity of O(n log n), hence it has advantage for practical use.