DTM correction in areas of steep slopes

Computation of a DTM from a DSM is a well-known and very important task. We derive the DTM by a procedure consisting of ground points extraction, surface interpolation and triangulation by a canonical mesh if the terrain is flat or has only moderate changes in elevation. In regions with steep slopes, such as at riversides, and with man-made 3D structures, such as around bridges, interpolation artifacts and suppression of high-resolution details can lead to coarse errors in local elevations even for the building detection task. The eligible regions must be therefore detected and at least locally reprocessed. For detection, we search for connected components of a certain minimum size with negative relative elevations. For reconstruction, we suppress the points with erroneously reconstructed DSM values and interpolate the surface by means of L1 splines. Finally, these meshes must be fused into one single DTM mesh. We applied land cover classification to demonstrate the usability of our correction. The overall accuracy amounts to around 88% while the number of faulty assignments due to incorrect DTMs can be significantly reduced.