Digital Terrain Models (DTMs)

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)

  • 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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Digital Surface Models (DSMs)

In a LiDAR system, pulses of light travel to the ground. When the pulse of light bounces off its target and returns to the sensor, it gives the range (a variable distance) to the Earth. Hence, how this system earned its name of Light Detection and Ranging.

In the end, LiDAR delivers a massive point cloud filled of varying elevation values. But height can come from the top of buildings, tree canopy, power lines and other features. A DSM captures the natural and built features on the Earth’s surface.

A DSM is useful in 3D modelling for telecommunications, urban planning and aviation. 

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Open Cast Mining

Open cast mining, also known as open pit mining, is a surface mining technique that extracts minerals from an open pit in the ground. Open-pit mining is the most common method used throughout the world for mineral mining and does not require extractive methods or tunnels. This surface mining technique is used when mineral or ore deposits are found relatively close to the surface of the earth. Open-pits are sometimes called ‘quarries’ when they produce building materials and dimension stone.


GeoTIFF is a public domain metadata standard which allows geo-referencing information to be embedded within a TIFF file. The potential additional information includes map projection, coordinate systems, ellipsoids, datums, and everything else necessary to establish the exact spatial reference for the file.

© 2020 by ATEC-3D.

Folkestone, Kent

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