The drainage network extraction from contour lines for contour line generalization

Unlike the simplification of independent line features, the generalization of terrain contour is to handle the “line group", which describes the geomorphologic characteristics, such as the terrain valley and ridge. In decision level, the real operation object in the terrain generalization is not the line segment itself but the drainage network contained in the contour representation. This paper presents a method to generalize contour based on the analysis of drainage structure. The first step is to extract the drainage system from the contour lines and build the associations between the valley branch and the bend group of contour lines. The second step is to analyse the properties of drainage tree structure to decide which branch to be removed, and then to perform the geometric elimination of bends. In this study the extraction of drainage system is directly from contour (other than from DTM data) based on the Delaunay triangulation model. Three kinds of tree structure organization are investigated: the hierarchical binary tree representing the bend inclusion relationship contained in each contour line, the planar structure tree describing valley topological relationship and the semantic hierarchical tree representing valley joint level structure from the point of view of hydrology.