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Đường nét từ Mô hình kỹ thuật số địa hình Đường viền sản xuất đã được một trong các ứng dụng truyền thống của DTMs. Chương này được dành cho việc sản xuất các đường nét từ DTM. 11,1 Tiếp cận với các đường nét từ DTM Các đường cong có thể được sản xuất hoặc lưới điện dựa trên tam giác dựa trên DTM, hoặc bằng cách một phương pháp vector hoặc raster. Như vậy, về mặt lý thuyết nói, sự kết hợp bốn cho đường nét từ DTM: 1. 2. 3. 4. vector dựa trên đường nét từ một mạng lưới dựa trên. | CHAPTER 11 Contouring from Digital Terrain Models Contour production has been one of the traditional applications of DTMs. This chapter is devoted to the production of contours from DTM. 11.1 APPROACHES FOR CONTOURING FROM DTM Contour lines could be produced from either grid-based or triangulation-based DTM either by a vector-based or by a raster-based method. Thus theoretically speaking four combinations are available for contouring from DTM 1. vector-based contouring from a grid-based DTM 2. vector-based contouring from a triangulation-based DTM 3. raster-based contouring from a grid-based DTM 4. raster-based contouring from a triangulation-based DTM. The first two approaches are widely used. Raster-based contouring from a gridbased DTM is not widely used although it is not difficult. Raster-based contouring from a triangulation-based DTM is not practical because the triangulations are normally for irregularly distributed data and thus it is not possible to form a raster structure without interpolation. It is possible to produce a stereomate for a contour map so that a stereo model of terrain can be seen if viewed using a stereoscope. This results in various approaches for contouring from DTM as shown in Figure 11.1. 11.2 VECTOR-BASED CONTOURING FROM GRID DTM There are many ways to produce contour lines from a grid DTM. The basic principles are similar although the procedures may differ. All methods in vector-based 233 2005 by CRC Press 234 DIGITAL TERRAIN MODELING PRINCIPLES AND METHODOLOGY Figure 11.1 Approaches for contouring from DTMs. approaches try to solve the following problems 1. to search for the starting point of each contour line 2. to interpolate the contour points by computing the coordinates of the intersection points between each contour line and grid edges 3. to trace contour lines 4. to smooth traced contour lines if desirable. 11.2.1 Searching for Contour Points To obtain all contour lines in the area of concern first the heights of the lowest
