Research And Implementation Of Continuous Distance-dependent Level Of Detail (CDLOD) Terrain Rendering Algorithms

Terrain rendering plays an important role in flight simulators, airborne navigation,geography information systems (GIS) and the application of video games. It is one of the hottopics in Computer Graphics research field. This paper mainly discusses continuousdistance-dependent level of detail terrain rendering algorithms to be applied to airbornenavigation project, which is a technique for GPU-based rendering of terrains and a refinementof several existing methods with some new ideas. It is similar to the terrain clipmapapproaches, as it draws the terrain directly from the source heightmap data. However, insteadof using a set of regular nested grids, it is structured around a quadtree of regular grids, moresimilar to Chunk LOD algorithms, which provides it with better level-of-detail distribution.The algorithm’s main improvement over previous techniques is that the LOD function is thesame across the whole rendered mesh and is based on the precise three-dimensional distancebetween the observer and the terrain. To accomplish this, a novel technique for handlingtransition between LOD levels is used, which gives smooth and accurate results. The mainachievements are listed as following:(1)LOD is based on the precise three-dimensional distance between the observer and theterrain.Therefore, the system is more predictable and reliable, with better screen-triangledistribution.(2)To deal with the cracks and Popping, the morph area is also defined. The algorithmused to transition between LOD levels completely transforms the mesh of a higher level intothe lower detailed one before the actual swap occurs. This ensures a perfectly smoothtransition with no seams or artifacts.(3)Utilizing the programmable features of GPU to deal with the morph area, which willbe running on GPU, by high level shader language so that it can reduce the workload of CPU.(4)Since CDLOD performs the transition between LOD layers using smooth continuousmorph of triangles with no discontinuities or T junctions, additional subdivision can easily beapplied on top without breaking the continuity that makes it a good platform for hardwaretessellation (Shader Model5).