DTM - Digital Terrain Model
FDTM - Filled Digital Terrain Model

DTM and FDTM are elevation models which depict the terrain surface without buildings and vegetation.

If, instead of the greatest elevation, the lowest elevation is assigned to a raster element, it still includes extensive objects above the terrain proper (large trees, buildings, etc.). These objects are usually visible and are eliminated by filter algorithms and interactive processing for generating a terrain model. In the filtered areas there is no elevation value representing the terrain elevation though. The same technical parameters as for the DSM apply to this DTM terrain model (with gaps). If the client so wishes, and if necessary for further processing, the gaps in the DTM which are due to the filtering can be closed by interpolation. This FDTM (filled DTM) then has no gaps. It is created only at the client’s request and is not subject to any quality control by TopoSys in the interpolated areas. Terms of acceptance always relate to the DTM and not to the FDTM.

For generating the DTM/FDTM, the filtering of the buildings and remaining vegetation is performed as standard on the elevation model from last echo, assignment of low values.

Here two examples of a DTM and an FDTM are depicted as relief images. The filtered out areas of the DTM were colored in red.