Mesh refinement for 3D terrain visualization

Terrain is one of the most important objects in cyber city visualization. For a large scale or detailed terrain visualization, the vast amount of data may lead to lower efficiency. Using multiple levels of detail (LOD) to present the same area based on viewing conditions and user requirements is a commonly adopted strategy for improving terrain visualization performance in assorted applications. However, when applying tile-based LOD to large-scale landscape visualization, there are still a few issues needed to be addressed. Firstly, conventional LOD systems often divided the data set into small tiles geographically. This may result in poor performance or abrupt LOD changes when dealing with large-area visualization projects, especially during the initial stage. A nested LOD system was developed to create a finer set of LOD tiles and a coarser LOD set for quick representation of large areas. Secondly, when visualizing a terrain by mesh tiles, there are usually discontinuities along tile edges, causing so-called T-junctions. A mesh-merging algorithm was proposed to refine the determined LOD meshes in order to eliminate T-junctions. This will produce seamless landscape scenes consisting of multiple tiles of different LOD layers. Experimental results with an area of 80,000 km ² at 40m×40m resolution DEM data set indicated that the developed visualization system can provide better adaptive LOD transitions. The system can also eliminate T-junctions along tile edges, providing more continuous and smooth landscape scenes during a fly-through or other visualization tasks.