Automatic Extraction of Terrain Skeleton Lines from Digital Elevation Models

Terrain skeleton lines, among the most significant elements of topographical maps, are the valley lines that connect the deepest points of valleys, and the ridge lines that connect the highest points of ridges. In order to obtain correct and enough information about land forms from a topographical map, skeleton lines have to be considered and portrayed together with contours. Their extraction has a great importance in the different areas. They can be gathered from contours, digital elevation models (DEMs) or digital images automatically besides land surveying or photogrammetric stereomodels. In this study, a program called ‘RidgeValleyAxisPicker’ written for extracting ridge and valley lines from DEMs is used. It is based on the algorithm of Profile Recognition and Polygon Breaking (PPA) developed by Chang, et al. (1998). ‘RidgeValleyAxisPicker’ differs with PPA from two aspects: (1) profiles are not used in target recognition step and thus all height points are considered as targets, (2) branch reduction process is performed iteratively. All of the DEM points in 10 meter grid distance that are used in the case study are automatically collected from a stereomodel for a map at the scale 1: 5000. At the end of the study, the results are compared with the original topographic maps at the same scale from several aspects. In conclusion, although the method described in this paper for automatic extraction of terrain skeleton lines from DEMs can be working with huge amount of data quite rapidly, there are some cartographic problems on the extracted lines.