The New Method for Quickly Generating DEM Based on Raster Contour-CSE

CSE is a new method for quickly generating DEM based on raster contour. DEM is the basic model for generating three-dimensional terrain feature and it has a wide variety of application in GIS, geonomy analysis, civil engineering and so on. Generally speaking, there are three main methods for building DEM. One is based upon stereomeasurement with features of needing sufficiency photog rammetry stereo-mate and expensive instruments. The second is built upon contour digitizing with the peculiarities of low request of the data source and instruments but a long production cycle. The third is built upon the outdoor measurement with the characteristics of high precision, high cost and lowefficiency.This paper introduces a new method named CSE(color substitute elevation)which is used for quickly generating DEM from a contour map by image processing. CSE includes four steps:① Editing the contour image, including wiping off the conglutination of differing contour lines and connecting the disconnect contour lines in order to make every contour line substantive and continuous. ② Drawing out a corresponding table of elevation and color index according to the circles of contour lines in the contour map. ③All pixels of the same contour lines are dyed with the same color by image processing according to a color-elevation corresponding table and the output of the map is a set of X, Y, ColorIndex. ④The value of the color-index in the set is substituted with the corresponding elevation in order to get the com pact contour data of the map. Then section interpolation based on contour raster image is used for generating grid DEM. Compared with the method of digitizing contour for building DEM, CSE has characteristics on 4 facets. For editing contour data, CSE only processes the conglutinant or disconnect contour lines, and digitizing contour method needs to followevery contour lines; On the facet of original data collect precision, CSE is without edit error, and digitizing contour method has to add manual following error; When setting the elevation value to contour lines, many contour lines can be dyed in groups, then the elevation value substitutes the color index automatically with CSE, but digitizing contour method does it one by one; In addition, for DEM interpolation, due to getting compact contour line data, CSE can do section interpolation based on contour raster image quickly by the technology of database index, but with digitizing contour method, a TIN(triangulated irregular network)is built from contour vector data firstly, and some morbid triangles must be edited, then DEM interpolation is carried out based on TIN. As the result of above characteristics, the production cycle is shorten by about 3 times with CSE method and the maximum error of DEM is less than a half of the contour-interval in the map. A number of practices have proved that the method for quickly generating DEM based on raster contour-CSE is absolutely viable.