A method of constructing undersea TIN DEM based on vector nautical chart

A method for constructing an undersea digital elevation model(DEM) was proposed,using the soundings and coastline elements in a vector nautical chart.Three new algorithms were developed,respectively: borderline simplification;feature lines insertion;boundary representation.First,an improved Douglas-Peuker(DP) algorithm named "piecewise DP simplification with feature nodes" simplifies borderlines.Compared with traditional DP methods,the improved algorithm is able to maintain the 2D measurements of the polygonal element,the quantity of meshes decreases,the quality of the mesh improves after simplification,with less construction time,and the borderline retains its shape well.Second,an improved node refinement algorithm for inserting feature lines was proposed.Compared with the existing node refinement algorithms,this algorithm ensures the validity and stability of triangulation.Third,since the boundary of a region cannot be represented by the standard Delaunay triangulation,an algorithm for representing rational boundaries of a region was also proposed.Finally the method was tested on 3 real nautical charts with different styles,and the corresponding constrained Delaunay triangular irregular networks(CD-TIN) DEMs are shown in 2.5D,which match the nautical charts well,with high quality meshes and little calculation time.The results show that the proposed method is applicable for mapping various undersea terrains.