Extracting Topographic Characteristic Lines Based on Constraint Delaunay TIN

In order to extract high-quality topographic characteristic lines,based on contour lines constrained Delaunay TIN,two employed methods of extracting the topographic characteristic lines are proposed in this paper.The first method is calculating the value of the turn angle, curvature and the shape index of contour vertex firstly,and then is to determine the threshold value according to the corresponding characteristic points set,with the rules the selected characteristic points will be connected to topographical lines .the second method is to take into account that Delaunay triangle is a triangle in 3-D space and calculate the flow direction of each small triangle at first,and then combination relations of the flow direction according to each two adjacent triangles of the public side is classified,the topographic characteristic lines are extracted according to the different edge types finally.The similarities and differences are compared through the experimental results,the existing differences is addressed in detail at last.