Differences between DEM, DSM and DTM?

  • I am listing some of the acronyms used in our work and had to stop to think about whether to list these together or separately:

    • DEM: Digital Elevation Model
    • DSM: Digital Surface Model
    • DTM: Digital Terrain Model

    In some circles they seem synonymous, in others they seem to have distinct meanings.

    Is there an agreed-upon definition for each that enables them to be distinguished?

  • underdark

    underdark Correct answer

    10 years ago

    In my experience, DEM is most of the time used as a generic term for DSMs and DTMs. I think this image on Wikipedia depicts the differences between DSMs and DTMs well:

    enter image description here

    • DSM = (earth) surface including objects on it
    • DTM = (earth) surface without any objects

    A different definition is found in [Li et al., DIGITAL TERRAIN MODELING - Principles and Methodology]:

    DEM is a subset of DTM and the most fundamental component of DTM.

    In practice, these terms (DTM, DEM, DHM, and DTEM) are often assumed to be synonymous and indeed this is often the case. But sometimes they actually refer to different products. That is, there may be slight differences between these terms. Li (1990) has made a comparative analysis of these differences as follows:

    1. Ground: “the solid surface of the earth”; “a solid base or foundation”; “a surface of the earth”; “bottom of the sea”; etc.
    2. Height: “measurement from base to top”; “elevation above the ground or recognized level, especially that of the sea”; “distance upwards”; etc.
    3. Elevation: “height above a given level, especially that of sea”; “height above the horizon”; etc.
    4. Terrain: “tract of country considered with regarded to its natural features, etc.”; “an extent of ground, region, territory”; etc.

    A DEM is not a generic name for a DSM and DTM

    Yes, there are numerous different definitions. I added a different one plus it's source.

    I also thought that DEM was used as a generic name for a DSM/DTM. Whats a DEM then?

    @Underdark I find this quotation deeply confusing, because it does not reveal what distinctions are intended between "height," "elevation," and "terrain." (Indeed, the description of terrain seems to imply they are talking about LULC data, not DEMs or DTMs!) Do you have a link that would provide fuller context to understand this?

    @Underdark Thank you. The correct link appears to be http://www.torabzadeh.bloghaa.com/files/2010/03/1.pdf, which exists but seems to run at a glacial pace... I'll keep trying.

    @Underdark I found it at http://tehran.academia.edu/aliasgharheidari/Books/194823/DIGITAL_TERRAIN_MODELING_Principles_and_Methodology. The fundamental distinction they make between DEM and DTM is that the DTM "will attempt to incorporate specific terrain features such as rivers, ridge lines, ..." Of all the answers so far, this distinction is clearly brought out only by @WolfODrade. In particular, the Wikipedia article on DEMs is useless in this respect.

    @underdark I do not think this is quite right. DTM has been misidentified by Li 1990 or it changed from 1990 to 2000 when I entered grad school to do GIS. AS 1990 is pre say lidar this may be the reason.

    @WolfOdrade this is the best answer due to the DTM component. I DTM changed usage in the late 90s.

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