Study And Implementation Of Three-dimensional Terrain

The three-dimensional visualization technology,as an important researchdirection in the field of computer graphics, has been widely used in the field of virtualreality, animation, movies, games, industrial design, etc, however, it has not oftenapplied in the field of Geographic Information System. In recent years,The people paymore attention to the field of Geographic Information System. The DEM,as animportant result of simulation of the digital terrain, has become one of the nationalspatial data infrastructure. Therefore, how to use the DEM to build the terrain is avery important issue. Terrain rendering is a very important link in thethree-dimensional terrain visualization technology, As the scale of terrain increasing,terrain precision is higher and higher. Traditional static rendering algorithms areinsufficient to meet the need for real-time rendering of terrain with a huge amount ofdata.This paper uses the OpenGL graphics library to complete terrain modeling andrendering experiment. Study deeply the DEM surface modeling, Analyze and comparethe method based on the TIN surface modeling and th based on the grid e methodbased on GridBoth, taking surface modeling method to build a3D mesh terrain. Thispaper analyze deeply the most commonly used LOD real-time terrain renderingalgorithms,take the common ROAM algorithm based on the binary triangle tree andcontinuous LOD terrain algorithm based on quadtree terrain rendering experiment tocomplete terrain simulation experiment,then compare the rendering efficiencybetween the two algorithms.This type of algorithms all take the principle of relate tothe point of view. According to the distace between the point of view and terrain nodeto change in real time to generate dynamically different precision terraingrid.Compared to the static terrain algorithm,this type of algorithm can effectivelyreduce the number of each frame of the computer rendering the triangle and improverendering efficiency.Tradional real-time rendering LOD algorithm based on quadtreehas two drawbacks.The first drawback is that the algorithm is easy to generate terrainT-shaped cracks.Traditional way of eliminatingthe terrain T-shaped crack is takingthe manner of adding edge or deleting edge.However,they have some limitation.Themanner of adding edge will increasing the number of rendering edges,the manner ofdeleting edge is only available to the condition that the LOD diffrence of adjacentnodes is one.The second drawback is that the algorithm uses the manner based onworld coordinates to complete the culling operate.Although the method is simple andIntuitive,it needs a lot of computing while determining whether the node is in thefrustum body and is not conducive to improve the terrain rendering efficiency.The innovation of this paper is to improve the two shortcomings of the algorithm.For the first drawback,this paper take the way that combine the manner of addingedge and the manner of deleting edge to eliminate the T-shaped cracks in the terrain.This method can be applied to the difference in the level of detail degrees betweenadjacent nodes for any number of circumstaces,but also improve the renderingefficiency.For the second drawback,this paper use the manner based on projection coordinates to select the node which is needed to render.the method only judgewhether the projection coordinate of each node is in the range from-1to1and don’tneed to do some test calculations in world coordinates,this method can well recuce theamount of compulation. The improved algorithm improves the rendering framerate,reduce the number of triangles required to render each frame,improves theefficiency of the algorithm.This paper uses the OpenGL graphics library to complete terrain modeling andrendering experiment,study the commonly used modeling method and renderingmethod.The experiment result shows that the rendering frame rate of the improvedalgorithm increase as much as30%,the amount of triangle needed to render of eachframe reduce as much as33%.The improved rendering algorithm which is valuable tothe practical applicatioin.