Slope Accuracy and Path Planning on Compressed Terrain

We report on variants of the ODETLAP lossy terrain compression method where the reconstructed terrain has accurate slope as well as elevation. Slope is important for applications such as mobility, visibility and hydrology. One variant involves selecting a regular grid of points instead of selecting the most important points, requiring more points but which take less space. Another variant adds a new type of equation to the overdetermined system to force the slope of the reconstructed surface to be close to the original surface’s slope. Tests on six datasets with elevation ranges from 505m to 1040m, compressed at ratios from 146:1 to 1046:1 relative to the original binary file size, showed RMS elevation errors of 10m and slope errors of 3 to 10 degrees. The reconstructed terrain also supports planning optimal paths that avoid observers’ viewsheds. Paths planned on the reconstructed terrain were only 5% to 20% more expensive than paths planned on the original terrain. Tradeoffs between compressed data size and output accuracy are possible. Therefore storing terrain data on portable devices or transmitting over slow links and then using it in applications is more feasible.