In this paper

a new method for automatic extraction of ridge and valley axes from DEM

named as Directional Profile Approach(DPA)

is proposed. DPA can automatically determine whether a grid point in DEM is a possible ridge(or valley) grid point

according to the features of the profiles through this grid point. Applying this new method to extracting ridge and valley axes automatically from DEM

the following several procedures must be accomplished: First

the all elevation grid points which may be located in ridge and valley lines are automatically recognized with DPA. Then the modified Hilditch thinning algorithm is applied to selecting the ridge and valley grid points recognized by DPA. Third

the every two neighboring ridge points or valley points are connected and rudimentary form of the ridge or valley axes is constructed. Finally

the closed triangles in ridge and valley axes are broken and the short branches are removed. A real DEM was used for testing data

the ridge and valley axes extracted automatically by this method can basically represent the topographic features of the corresponding topographical map. Therefore

this new method is effective.