Geometry clipmaps: Terrain rendering using nested regular grids

Geometry clipmaps: Terrain rendering using nested regular grids
Frank Losasso, Hugues Hoppe.
ACM Trans. Graphics (SIGGRAPH), 23(3), 2004.
New terrain data structure enabling real-time decompression and synthesis.
Abstract: Rendering throughput has reached a level that enables a novel approach to level-of-detail (LOD) control in terrain rendering. We introduce the geometry clipmap, which caches the terrain in a set of nested regular grids centered about the viewer. The grids are stored as vertex buffers in fast video memory, and are incrementally refilled as the viewpoint moves. This simple framework provides visual continuity, uniform frame rate, complexity throttling, and graceful degradation. Moreover it allows two new exciting real-time functionalities: decompression and synthesis. Our main dataset is a 40GB height map of the United States. A compressed image pyramid reduces the size by a remarkable factor of 100, so that it fits entirely in memory. This compressed data also contributes normal maps for shading. As the viewer approaches the surface, we synthesize grid levels finer than the stored terrain using fractal noise displacement. Decompression, synthesis, and normal-map computations are incremental, thereby allowing interactive flight at 60 frames/sec.
Hindsights: In our more recent GPU Gems 2 chapter, we store the terrain as a set of vertex textures, thereby transferring nearly all computation to the GPU. (See the demo available there.)

The PTC image compressor mentioned in the paper was the precursor to the JPEG XR standard, which is supported in the WIC interface of Windows.

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