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Overlaying vector data on 3D terrain

3D terrain visualization is an important function in 3D GIS. Traditional methods emphasis on the real displaying of 3D terrain and its simplification, they ignore the analysis functions on the spatial data. This paper proposed a method that can display vector data on 3D terrain surface and we can make spatial analysis according to these vector data. Terrain surface is composed of DEM grids and every grid can be divided into two triangles. The vector data rendered on terrain can be considered as a part of the triangles. Given that a 2D point which including (x,y) information, we can get the third dimension information by spatial interpolation. Then we can draw arcs and polygons on terrain surface based on these 3D point data. It must adopt special methods to avoid the vector data displaying above or below the terrain surface. When drawing arcs on terrain surface, we tried out all intersection points between arc lines and triangles' edges so as to ensure the arc cling on the surface. When drawing polygons on terrain surface, we designed a recursive algorithm to connect local triangular nets for the 3D polygon so that the polygon can cling on the surface too. Finally, the author applied this method on the visualization of 3D terrain of JingJiang regions of China and obtained a good effect