A Robust Divide and Conquer Algorithm for Progressive Medial Axes of Planar Shapes

The medial axis is an important shape representation that finds a wide range of applications in shape analysis. For large-scale shapes of high resolution, a progressive medial axis representation that starts with the lowest resolution and gradually adds more details is desired. In this paper, we propose a fast and robust geometric algorithm that computes progressive medial axes of a large-scale planar shape. The key ingredient of our method is a novel structural analysis of merging medial axes of two planar shapes along a shared boundary. Our method is robust by separating the analysis of topological structure from numerical computation. Our method is also fast and we show that the time complexity of merging two medial axes is O(n log nv), where n is the number of total boundary generators, nv is strictly smaller than n and behaves as a small constant in all our experiments. Experiments on large-scale polygonal data and comparison with state-of-the-art methods show the efficiency and effectiveness of the proposed method.The topographical data used in Table 2, Figs. 1 and 24 is courtesy of U.S. Geological Survey. The authors also thank the CGAL Open Source Project (https://www.cgal.org/) to make the CGAL software public available. This work was supported by the Natural Science Foundation of China (61322206, 61521002, 61432003) and the NRF grant funded by the Korea government (2012R1A2A1A05026395)