Chapter 2 Terrain Rendering Using GPU-Based Geometry Clipmaps

The geometry clipmap introduced in Losasso and Hoppe 2004 is a new level-of-detail structure for rendering terrains. It caches terrain geometry in a set of nested regular grids, which are incrementally shifted as the viewer moves. The grid structure provides a number of benefits over previous irregular-mesh techniques: simplicity of data structures, smooth visual transitions, steady rendering rate, graceful degradation, efficient compression, and runtime detail synthesis. In this chapter, we describe a GPU-based implementation of geometry clipmaps, enabled by vertex textures. By processing terrain geometry as a set of images, we can perform nearly all computations on the GPU itself, thereby reducing CPU load. The technique is easy to implement, and allows interactive flight over a 20-billion-sample grid of the United States stored in just 355 MB of memory, at around 90 frames per second. 2.1 Review of Geometry Clipmaps In large outdoor environments, the geometry of terrain landscapes can require significant storage and rendering bandwidth. Numerous level-of-detail techniques have been developed to adapt the triangulation of the terrain mesh as a function of the view. However, most such techniques involve runtime creation and modification of mesh structures (vertex and index buffers), which can prove expensive on current graphics architectures. Moreover, use of irregular meshes generally requires processing by the CPU, and many applications such as games are already CPU-limited