Visualization In Three-dimensional GIS And Vector Map Symbol Display

At present, almost all the geographic information system (GIS) is two-dimensional, however, As the needs increasing everyday, three-dimensional GIS gains more and more attention, three-dimensional geographic information system is getting perfect by degrees. 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 show two-dimensional map symbols in the three-dimensional GIS is becoming a research direction nowadays.Three-dimensional GIS data model can be divided into three categories, physical model, surface model and mixed model. Physical model data structure includes solid geometry model structure, three-dimensional grid structure, octree structure. Surface model data structure includes TIN, Grid, parameters of function and boundary representation. Mixed model data structure includes Octree-TEN mixed modeling, TIN-CSG mixed modeling, TIN-Octree hybrid modeling. Afterwards, complete the three-dimensional data model building, you have to achieve three-dimensional data visualization, the commonly used tool is Java 3D, DirectX, OpenGL and VRML. Now commonly used methods in GIS mapping symbol are drawing portfolio, pure function drawing, drawing and line loop method.This paper select Java 3D and Java as the development tools, analyze DEM files to build three-dimensional arrays, and further build Grid data structure, Using Java 3D technology 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 of three-dimensional terrain and polygons, determine the range of three-dimensional terrain intersection, and then search out the point of the range, and then build a new triangular facets, then displayed in the three-dimensional scene finally.By building terrain and running the program, achieve the visualization of the three-dimensional terrain 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.