Skeleton based contour line generalization

Contour lines are a widely utilized representation of terrain models in both cartography and Geographical Information Systems (GIS). Since they are often presented at different scales there is a need for generalization techniques. In this paper an algorithm for the generalization of contour lines based on skeleton pruning is presented. The algorithm is based on the boundary residual function and retraction of the skeleton of contour lines. The novelty of this method relies on pruning not only the internal skeleton branches, but also those skeleton branches placed outside the closed contour polygon. This approach, in contrast to original method which was designed for closed shapes is capable of handling also open polygonal chains. A simplified version of the skeleton is extracted in the first step of the algorithm and in the next a simpler boundary is computed. The simpler boundary as shown in this paper, can be found using three different ways: detection of stable vertices, computation of an average vertex and approximation of the boundary by Bezier splines.