DEM versus DTM versus DSM

There are a few terms that I find to be especially confusing to the community of people who use our geospatial software.  I thought it might be useful to clarify how I and others at Exelis VIS use some of those terms.  In this post, I’ll cover DEMs, DTMs, and DSMs.  Look for a future post about the terms georeference, geolocate, and georectify.

The terms DEM (Digital Elevation Model), DTM (Digital Terrain Model) and DSM (Digital Surface Model) are all usually used to refer to various types of continuous, three-dimensional geospatial data.  There is a fair amount of confusion in the literature, however, about which term refers to which types of data.  If you want to get really confused about these terms, there is a great Wikipedia article that goes into confusing detail about this terminology confusion.

A DEM of the area around Boulder, Colorado.

A DEM provided by the USGS for the area around Boulder, Colorado.`

In the world of ENVI, we really only use the term DEM.  A DEM in ENVI is understood to be an image (raster) in which the pixel values represent the ground elevation above sea level.  If there are buildings, trees or other features on the ground in the area of a given DEM, those features are assumed to not be included in the elevation values included in the DEM.

In E3De, our new LiDAR visualization and analysis software environment, the documentation includes all three terms.  A DEM in E3De is understood to be an image (raster) or a set of vector contours, in which the values (pixel values or contour levels) represent the ground elevation above sea level.  A DSM in E3De is understood to be an image (raster) in which the pixel values represent the elevations above sea level of the ground and all features on it.  So, if there are buildings or trees in the area, for example, the DSM can include those building and tree heights in the elevation values it provides.  E3De does not create any datasets that it refers to as DTMs, but the documentation for E3De does refer to DTMs in a couple of places.  Where it does, it means a raster DEM.  In other words, to E3De, a DTM is an image (raster) in which the pixel values represent the ground elevation above sea level.

I hope this clears up confusion around these terms, at least regarding how they are used in the world of Exelis Visual Information Solutions.

How do you use the terms DTM, DSM, and DEM?

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10 Responses to DEM versus DTM versus DSM

  1. Devin White says:

    The part of the geospatial community that I support tends to use the three terms as follows:
    DEM = Regularly gridded 2.5D representation of a three-dimensional scene whose per-pixel values are referenced to Mean Sea Level. DTM and DSM are specific DEM types.
    DTM = Bare earth DEM, where things like trees and buildings have been removed.
    DSM = Equivalent to shrink-wrapping a 3D scene, so you see the tops of trees, buildings, etc.

  2. From a surveying and engineering perspective, we use the terms DTM and TIN most often. Surveying software generally works with TIN surfaces, so that’s what we are most familiar with. A TIN is a triangulated irregular network. We also import surfaces from other sources – generally a DEM.

    • Peg Shippert says:

      Hi Paul,

      Thanks for letting us know what you use most. And do you define DTM and DEM the same way I do, or as Devin does in his comment, or another way?

      – Peg

  3. Scott says:

    Another key to differentiating between a DSM and a DTM, is that a DTM will be produced with breaklines.

  4. kartik says:

    THANKS
    I LEARN SOM THING

  5. Sekhar says:

    Hello Sir,
    As I understood from the literature, what Mr.Devin said (He said, “DTM and DSM are specific DEM types”) can be modified as “DEM and DTM are specific cases of DSM”.
    DSM: Represent any surface, not necessarily elevation/terrain, like for example, population
    density, as pixel value.
    DEM: Represent the elevation, in civil engg. sense, that is heghts of features above mean sea
    level,
    DTM: Represent only the terrain, excluding the height of surface features.

    Regards,
    Sekhar

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