Digital Terrain Models

What is a Digital Terrain Model (DTM)?

When you refer to the USGS LiDAR Base Specification, a digital terrain model (DTM) actually has two definitions depending on where you live.

Digital Terrain Model (DTM)
Digital Terrain Model (DTM)
  • In some countries, a DTM is actually synonymous with a DEM. This means that a DTM is simply an elevation surface representing the bare earth referenced to a common vertical datum.
  • In the United States and other countries, a DTM has a slight different meaning. A DTM is a vector data set composed of regularly spaced points and natural features such as ridges and breaklines. A DTM augments a DEM by including linear features of the bare-earth terrain.

DTMs are typically created through stereo photogrammetry like in the example above. For example, contour lines are in purple. The DTM points are regularly-spaced and characterize the shape of the bare-earth terrain.

In the image above, you can see how the DTM is not continuous and that it’s not a surface model. From these regularly-space and contour lines, you can interpolate a DTM into a DEM. A DTM represents distinctive terrain features much better because of its 3D breaklines and regularly spaced 3D mass points.

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