Wavelet-Compressed Terrain Provides On-the-Sphere Rendering.
TerraBlocks™ is TerraMetrics’ proprietary use of wavelet-compressed terrain datasets and terrain-block rendering specifically suited for the mission-critical flight environment. TerraBlocks™ is not another TIN (triangular irregular network) or CLOD (continuous level-of-detail) approach to store and render terrain. Rather, TerraBlocks™ is a unique approach that provides efficient terrain storage and run-time retrieval, zero-error terrain storage and near-field rendering, and consistent, deterministic rendering regardless of terrain features.
Wavelets for Terrain Storage?
Virtually all authored terrain datasets originate as regular-gridded raster arrays of elevation heights (e.g.,
DTED®s, DEMs, DTMs). Wavelets are extremely well suited for compression of raster arrays and inherently provide powers-of-2 levels-of-detail (LOD) reconstruction capabilities. Additionally, arbitrary blocks of terrain data at any arbitrary LOD can be efficiently extracted in real time from a wavelet-compressed terrain dataset.
TINing approaches have been used as a method of vertex thinning—and correspondingly, polygon count reduction—to achieve increased terrain-rendering display rates. The problem with TINed terrain models is that errors are created in the models at author time, and vertices within the models must use world-space floating point coordinates because of their spatially irregular nature. The typical result is a single-LOD terrain model with built-in errors and absolute coordinates for every vertex. As terrain roughness increases or model error requirements decrease, TIN model sizes increase rapidly. TerraBlocks™ terrain data wavelet-compression maintains controlled data size regardless of terrain roughness, error requirements or the number of available LODs. All vertex coordinates are stored as small local-offset data types.
are hard-coded terrain errors and UTM zone gaps.
Mission-critical flight applications require “on-the-sphere” rendering and
uniform-grid terrain models for wide-area consistency and display accuracy.
VisSim applications still use “flat-Earth” terrain models based on TINed terrain methods. The results
Individual TerraBlocks™ are extracted at render time and processed as packets. Blocks are accessed and processed at viewpoint-appropriate LODs. Block seaming and parent-child interpolation provide smooth, continuous LOD vertex transitioning, which eliminates vertex popping. In the final render cycle, TerraBlocks™ are placed “on the sphere” relative to the viewpoint. This makes efficient use of the render pipeline, provides on-the-sphere rendering and produces zero visual rendering artifacts. TerraBlocks™ makes applications such as synthetic vision for approach and landing, and low-level, zero-visibility flight a reality for commercial transport and military applications.