Terrain landform features play major roles in such fields as geomorphology type recognition

relief map generalization

DEM construction and hydrology analysis. This paper presents an automatic method to extract terrain landform features and organize drainage system into tree structure based on bend assessment using Delaunay triangulation model. Compared with traditional DEM or TIN based methods

this pure vector approach obtains not only the topological structure of drainage system in planar graph

but also the valley distribution polygon range. Depending on geometrical computation and judgment of vector line

polygon

the structured properties in drainage representation is enhanced

avoiding the case of noise disturbance in DEM based method. The core algorithm makes use of the ability of Delaunay triangulation in detecting hierarchical structure of each contour line. Three kinds of tree structure organization are discussed: the hierarchical binary tree representing bend inclusion relationship contained in single contour line

the plane structure tree representing valley topological relationship

the semantic hierarchical tree representing valley join level from the point of view of hydrology. This paper gives systemically experiment and detailed comparative analysis.