Research And Implementation Of Vector Map Symbol Visualization In Three-dimensional GIS

Traditional geographic information system (GIS) is mainly two-dimensional, As the needs of production and life, three-dimensional GIS is gaining more and more attention, three-dimensional geographic information system is gradually perfected. Map symbol is a basic tool for the expression of map content, it can not only show the things that the spatial location, shape, nature and amount of features, but also that the relationship between various things, and regional general characteristics. Map symbols has been widely used in the two-dimensional map, has also been recognized and accepted by the people.How to display two-dimensional map symbols on the three-dimensional GIS is now a research direction.Three-dimensional GIS data model can be divided into three categories, physical model, surface model and mixed model. Physical model data structure include three-dimensional grid structure, octree structure, the solid geometry model structure. Surface model data structure include Grid, TIN, boundary representation and parameters of function. Mixed model data structure include TIN-CSG mixed modeling, TIN-Octree hybrid modeling, Octree-TEN mixed modeling. After completion of building three-dimensional data model, you need to achieve three-dimensional data visualization, the commonly used tool is OpenGL, VRML, DirectX, and Java 3D. Now commonly used methods in GIS mapping symbol are pure function drawing, drawing portfolio, drawing and line loop method.This paper select Java and Java 3D as a development tool, analyze DEM file to built three-dimensional array, and further build Grid data structure, Using Java 3D technology to build three-dimensional terrain to achieve visualization of three-dimensional scene.Drawing point symbols:positioning technology to determine the first use of symbols in the three-dimensional terrain map coordinates, and then drawing method using pure function vector map display dot symbol. Draw line symbol:by fold method, the original line ups and downs according to terrain, generate off line, then draw the linear vector map symbols. Plane symbol drawn:the intersection polygons and three-dimensional terrain, determine the range of three-dimensional terrain intersection, and then search out the point of the range, and then build a new triangular facets, and finally displayed in the three-dimensional scene.By running the program, building terrain, achieve three-dimensional terrain visualization by analyze DEM data. Achieved point, line and area vector map symbols display in three-dimensional terrain and complete the zoom map symbol in interactive process.