Auto-reconstructing Broken Contour Lines Extracted from Raster Topographic Maps

There often are various gaps on the extracted contour lines images after color raster topographic maps’ segmentation, which affect digitalizing contour lines quickly and automatically. In order to realize broken contour lines’ accurate matching and connection as many as possible, an efficient approach for broken contour lines’ automatic reconstruction is proposed in this paper. Firstly, the algorithm of multiple incremental back-tracing and getting weighted average of endpoint’s directional angle is designed for enhancing the precision of endpoint’s directional angle; then max constraint angles control mechanism with multiple graded ranks is used to control transitional smoothing degree, and obtain the chosen endpoints satisfying the condition; lastly, the algorithm combining weighted Euclidean distance and offset angle between endpoints is put forward to determine the optimum matching endpoint. Besides, bidirectional matching algo-rithm based on parabola shape is supplemented to solve the remaining complicated and acute end points located in ridge and valley areas. The end points close to the map’s edge are also prolonged in their respective line direction until reach the edge of map. The comparative experimental results indicate that the proposed approach holds higher accuracy and completeness, better stability and applicability.