Digital Terrain Model (DTM)
A DTM, Digital Terrain Model, records the height of the bare ground, with objects above it filtered out. It is the site as it would look with the buildings and vegetation removed.
Like the DSM, it is a digital elevation model, a raster that stores one height value per pixel. DTM maps are the version civil engineers and surveyors usually want, because the ground is what gets cut, filled and drained.
Download format: GeoTIFF, with elevation values stored per pixel.
What it is used for
- Earthworks and grading. Cut and fill planning on the actual terrain.
- Drainage and water flow analysis.
- Contour lines, which describe the ground rather than what sits on it.
- Slope and terrain analysis for planning and design.
DTM or DSM
- Interested in the ground itself? Use the DTM.
- Interested in what stands on the site? Use the DSM.
The DTM is derived by filtering objects out of the reconstructed surface. Dense vegetation and built-up areas leave less visible ground, so the terrain there is interpolated rather than directly measured.
Both models open as layers in the viewer, where you can take height measurements.