The Research Of Terrain Rendering Algorithms Based On Level Of Detail

Terrain rendering is a core part of an outdoor scenes rendering engine, and isalso one of the hot topics in Computer Graphics research field. It plays animportant role in the application of video games, geography information systems(GIS), flight simulators and the virtual reality (VR) systems. When we want togenerate a scene with quite a lot of reality, it is usually not possible to satisfy therequest of real-time response in interactive operations because of the complexityof the scene. Then how to simplify the terrain, abandon unwanted renderingactions (such as render invisible triangles and needless details) to quickenrendering speeds becomes the key point of the realization of a large-scale terrainrendering system. Dynamic LOD technology is doubtless a powerful solution.Level of Detail (LOD) is a technology that accords with people's sense ofvision characteristic. At prior condition that does not affect the visual effect ofthe scene, it can reduce the scene's geometry complexity by gradually simplifythe scenery's surface details; thereby improves the efficiency of the renderingalgorithms. In interactive time of real time, according to the location and line ofsight got along by current moment of the observer, we adopt the high-accuracymodel terrain piece in close area and low-accuracy terrain piece in distance area,so that we can reach the premise of displaying the graphics in real time,harmonize between the sense of reality and rendering speed, and rise the goodvisual effect in Maximal degree.This thesis mainly discusses the real-time terrain rendering algorithms basedon LOD. The third chapter of this thesis has analyzed the basic thought of terrainalgorithms based on quad tree, expatiated the construction process of QuadTree and several key problems while rendering, and generated the continuousLOD regular square grid using adaptive quad trees; the fourth chapter hasintroduced the terrain algorithms based on binary tree, mainly studied the mostpopular ROAM algorithm, finally realized the algorithm and analyzed the result; the fifth chapter has given a detailed explanation to the Progressive Mesh (PM)algorithm. First introduced the basic idea of the algorithm, and then realized thestatic construction of the Progressive Mesh. At the same time, we improved onthe algorithm, at the computation of the collapsed edge's cost, we considered thefact that a surface which is coplanar needs less polygons to represent, and we alsoadded the restriction condition of the edge which will be collapsed, that is anedge which includes a boundary point can not be collapsed, for fear that theterrain boundary distort a lot. Finally we realize the view-dependent rendering oftriangulated irregular network with operations of edge collapse and vertex split.In the end, we have made a conclusion of the jobs done above, pointed outthe places where need to be improved, and put forward the expectation of futureworks.