Extraction of Ridge Lines from Grid DEMs with the Steepest Ascent Method Based on Constrained Direction

Abstract

The extraction of ridge lines from digital elevation models is fundamental for generalizing digital elevation models (DEM ), analyzing digital valleys, remote sensing analysis, and topographic indices analysis. In this paper, the authors propose a method to extract ridge lines from a gridded DEM called the Steepest Ascent Method Based on Constrained Direction (SAMBCD). In the SAMBCD method, based on the overland flow simulation method and the steepest ascent method, the authors define control points and constrain the direction of connecting points in the process of organizing major ridge lines and minor ridge lines, respectively, among the discrete points of the catchment boundary. Specifically, with SAMBCD, the points on hill peaks and saddle points are first sorted and used as control points to constrain the connecting direction. Second, the major ridge lines are organized by connecting the relevant discrete points of the catchment boundary, following the constrained direction. Finally, the remaining discrete points of the catchment boundary are connected to form the minor ridge lines with the same constrained connecting direction. Many tests are performed to extract ridge lines in different regions. The results show that the method of SAMBCD is effective for decreasing the fracture, cross and rotation of extracted ridge lines. Moreover, SAMBCD has better performance in the continuity and integrity of ridge lines than the two basic methods mentioned above.