Talk:Digital elevation model

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Proposed Merge of DTM and DEM[edit]

A DEM is digital representation of topographic surface while a DTM is derived from a DEM. A DEM is a dataset with elevation data in digital format and that is it. A DTM refers to terrain features in digital format represented as an image, of a grid showing elevation, slope, aspect, drainage sinks, etc...DTMs are almost always a regular grid. DEMs can be a regular grid, digital contour lines, a TIN (triangulated irregular network)of a profile or series of profiles. --Ray 11:45, 28 December 2005 (UTC)

This is the first time I've seen DTM, but I've seen many occurrances of DEM. It's not my field, though. With redirects, it probably doesn't matter. Mainly I'm commenting because no one else has.Walter Siegmund (talk) 02:46, 9 February 2006 (UTC)

DTM is a subset of DEM[edit]

DEM is definitely a more broad term than DTM, and is more extensively used in the GIS field. It would be better to roll DTM into the DEM article. —This unsigned comment was added by 18:18, 24 March 2006 (talkcontribs) .

I agree with this comment. The DTM topic should be included in the DEM article and not the other way around. (SCmurky 18:11, 25 May 2006 (UTC))

DTM Differs from a DEM[edit]

I agree with the first posting. The DEM is a numerical data file. Sometimes it is rendered as an image whereby the numerical elevation values are mapped to pixel values, producing the familiar ghostlike greyscale images that only vaguely remind one of the underlying terrain. The DTM is an image derived from a graphical rendering of the DEM. The starting point is called a heightfield that is an object generated by a graphics program capable of producing shaded images, like OpenGL. The DTM is supposed to look something like the terrain from which the DEM data was obtained. —The preceding unsigned comment was added by (talkcontribs) 15:28, 16 April 2006 (UTC)

So, this agrees with the second post too, then - DTM should be merged as a sub-topic or extension of DEM, not the other way around.—The preceding unsigned comment was added by (talkcontribs) 23:46, 30 May 2006 (UTC)

Changed Merge directions[edit]

As I agree with the above discussion that DEM is the wider topic, I've gone ahead and changed the direction on the merge tags. Whitejay251 05:06, 5 June 2006 (UTC)

Good to see progress in this discussion. Walter Siegmund (talk) 05:49, 5 June 2006 (UTC)

There should be one article, covering both DEM and DTM. Viewfinder 08:56, 5 June 2006 (UTC)

I have implemented the merge. Please elaborate on the differences between DEM and DTM, and cite any published sources. +mwtoews 21:29, 15 February 2007 (UTC)
I like the merge, so far. IMHO, the distinctions between a DEM, a DTM and a DSM have not been well defined in the literature and I don't believe that any such distinctions are largely accepted within the larger geospatial community. DEM is certainly the most used term for any type of terrain surface representation, but I see the others used from time to time. I have not heard the terms "heightmap" or "heightfield" used.
I'll agree with the lack of DEM vs DTM differences, and I have commented out that section unless there is anything found that has been published. The discussion with "heightfield" is an independent discussion, found below, so let's try not to confuse too many things at once.+mwtoews 16:59, 22 March 2007 (UTC)
The difference between a DEM and a DTM in terms of naming conventions certainly isn't universally observed in the remote sensing community, but I think there is at least enough common ground in terms of usage that it's worth discussing in the article. In terms of references, a quick google search brings up definitions from the UK Environment Agency [1] and Infoterra [2] (a leading UK remote sensing company), would they be adequate? I could look for some journal references if not, when I get a minute. Eve 17:18, 22 March 2007 (UTC)
Yup, that's defiantly a good start, and I've added those two references. If you do find any journal references, that would be good, but I wouldn't stress about it too much. Probably a good source would be about processing DTMs from DEMs for flood management or something along those lines. +mwtoews 21:10, 22 March 2007 (UTC)

In geospatial circles, the terms "bare earth" or "bald earth" are often used as a modifier to mean a DEM that does not include features above ground level - e.g., trees, buildings, etc. DEMs that do include features above ground level are often referred to as "reflective surface" DEMs. This distinction is important because generating DEMs from many remote sensing techniques can only give this reflective surface type DEM. These DEMs have to be manually edited to create a bare earth DEM. As an example, the original DTED DEMs were bare earth, and extensive manual editing was required to adjust the height of tree canopy down to the ground based on approximations. SRTM DEMs are true reflective surface DEMs. A few techniques (high resolution LIDAR, Foliage Penetrating SAR) can give bare earth DEMs directly, but those are still a small percentage of DEMs.

I'm interested in helping out with this topic, but don't really know where to start. Any thoughts on what needs emphasis? Tjamison 20:59, 16 March 2007 (UTC)

Merge with Heightmap[edit]

There had been some discussion about merging at Talk:Digital terrain model. Whitejay251 05:07, 5 June 2006 (UTC)

Yes with desribe differences between DEM and DTM

A DEM often implies a heightfield that is georeferenced, i.e., DEMs are more explicitly about terrain whereas heightfields are more general-purpose. Since DTM has 'terrain' in its name, it definitely implies terrain.

Another difference is that neither DEM nor DTM strictly mean "raster-based", whereas heightfields are. DEM would be a good general page about all sorts of digital elevation models, but heightfield would still be a concept unto itself.

my simple interpretation DTM refers to terrain ie: where the earth or rock stops. Everything else is ommitted. DEM refers to anything ie: tops of tree canopy, teeth, cricket pitches etc

g (land surveyor)

I've roughed in the merge, keeping DTM as a larger concept of which DEM is a subset (see for example the def here; please feel free to clean up. This is not my primary area of expertise, so I've mostly just sorted between the two articles.--Natcase 15:40, 7 December 2006 (UTC)

Do not merge. In a certain sense, heightmaps are "special cases" of DEMs. As said above, DEMs usually carry much more information, can be polygonal and non-uniformly sampled. Heightmaps by contrast are usually quadrilateral and uniform. Heightmaps are being used in completely different market areas. Merging just doesn't seem a good idea.
MaxDZ8 talk 10:21, 31 December 2006 (UTC)


There's a good image located here: Maybe you could get permission to use it? 05:57, 6 October 2006 (UTC)

Revised the article[edit]

The article was not reflecting the (unfortunately) manifold different definitions of the terms DSM, DTM and DEM. In fact most of the datasets introduced (ERS, SRTM, ASTER GDEM) are not DEMs like defined before (..of ground surface..). All datasets who use satellites or airplanes as platforms are DSMs. It is possible to create a DTM from a high resolution DSM dataset trough complex algorithm. I hope the article, is now reflecting the different types of definitions. I know there are other terms like Digital Height Models, Digital Elevation Terrain models, Digital Ground Models, etc., but I think DSM, DTM and DEM are the important onces. MO — Preceding unsigned comment added by MartinOver (talkcontribs) 20:03, 21 January 2011 (UTC)

Uses: Precision Inertial Guidance of Ballistic Missles[edit]

Prior to any more modern application of this type of advanced science and engineering to private or non-military governmental, highly accurate topographical, and compositional, information of the earth's surface were used to program flight paths into the inertial guidance computers of ICBMs. This information was used to accurately predict/assume/infer the value of the Earth's gravitational constant (g) at points of known elevation above the earth's surface along a predefined flightpath... such as the flightpath from the midwestern US, over canada, the arctic, and into Russia. It is necessary to know both topographical information in fine detail, as well as certain compositional information (eg the density of the terrain) to program these types of guidance systems to ensure a high degree of targeting accuracy. During the cold war, this information was synthesized from aerial and spaceborne reconnaissance, and even painstaking on-the ground geographical and geological studies. (talk) 19:17, 23 November 2015 (UTC)

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