Automatic Gap Identification towards Efficient Contour Line Reconstruction in Topographic Maps

Automatic extraction and vectorization of contour lines from color topographic maps is an important precursor to obtaining useful information for many vector based GIS applications. In this work, a novel hybridized algorithm is developed for reconstructing the extracted contour lines from color topographic map. The extraction of contour lines from a topographic map leads to broken contour lines due to inherent characteristics of the map, thus posing a challenging problem of identifying gaps and then filling them. This has been addressed by developing algorithms based on connected components, graph theory, expectation maximization (EM) and numerical methods. Our algorithm operates by isolating the segments of those contours which have gaps and achieves in reducing the complexity of the matching of such segments by employing the EM algorithm. We also present a new scheme of filling gaps present in thick contours without the application of thinning algorithms.