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Maybe this is a silly question: are DTM files a special type of files, similar to *.DWG, *XLM, *.DOC or *XLS, etc? or it just refer to a "type of model" (i.e. a representation of a land surface in 3D)?

For example, if somebody ask you to prepare a DTM file, what do you do? My understanding is that if I do a surface in Civil 3D that is my DTM file although it is a *.DWG file. Is this correct?

By the way, is DTM the abbreviation of "Digital Terrain Model"?

Thanks for your help.


Can you use Civil3D to generate a DTM file? Is a XML file considered a DTM file?

Thanks for your input...


A file with a ".dtm" extension is produced by Bentley system InRoads, and contains 3-d terrain data. Some people use the term "DTM" to refer to any file with 3-d terrain information, such as can be created by Civil 3D. I'd say it's likely your civil 3d file will suffice. Depending on what software they use, you might have to dumb down the terrain information, such as exporting it and exploding it so it's just 3d faces.


CarlB, so there is a *.dtm file which only can be generated by Bentley Inroads. This is good to know. I have that software but I have not used it yet. Do you have a reference I can follow in order to create the *.dtm files?

Thanks both for your responses.


CarlB, thanks. I saw some good videos in Youtube. Will look for the manuals as well. Thanks again for your help.


A DTM is a Digital Terrain Model. A file extension of *.dtm may be a "brand" of DTM, but there are many other formats (propriety). LandXML is a file format used to exchange Civil/Survey data between different design platforms.

A DTMs are typically a Triangular Irregular Network (TIN) or a grid. Previous posts in this thread seam to focus on the grid format, but TINs are common (and many times preferable, more accurate in Civil site design). In the GIS world, Grids (which can even be in an image format like TIFF) are more common.

I do not work with Autodesk Civil 3D, but I know it can produce TIN or Grid Digital Terrain Models (I use Carlson civil software). Civil 3D refers to DTMs as "Surfaces". Civil 3D can import and export surfaces to LandXML files for data exchange.


Terry, so a *.dtm file may also mean a TIN surface or a LANDXML file? I am totally confused. When working in Bentley Inroads, I cannot "save as" *.dtm, since an option for that extension is not available. My client is the USACE, so does anybody knows what they may be expecting? I would need to talk with them but in the meantime if anybody has any experience working with USACE and *.dtm files, any input will be greatly appreciated. Thanks all for your responses!!


I am checking and looks like I have to create a surface in Inroads in order to be able to save it as .dtm.
I can create the surface importing a LANDXML file. In Inroads there is a command called "translate" to do this. Will try again and post here if I find the solution...thanks!!



I attempted to differentiate a DTM (the generic model) from *.dtm (a specific file format). It is like talking about a text document DOC vs. Microsoft's *.doc file type (there are many other word processor file types).

Any time one is dealing with digital file deliverables, one needs to establish the specific file types and versions expected.


TerryScan, thanks for the clarification. It is more clear now. BTW, appears that we may be able to create *.dtm files in Bentley Inroads. We are trying to create a surface in Civil3D, then create the XML file, and finally export it into Inroads to create the *.dtm file. Hope it will work okay. I will update later. Thanks all again...!!


I agree with TerryScan, a TIN is the best exchange format. We used to run EaglePoint on AutoCAD and Microstation (MS) as well as GeoPak on MS. Easiest exchange at that point between the platforms was to "TIN the TIN" using the 3D triangles in the drawing. If you are worried about drawing size by adding the TIN to the DWG, write it out to a separate drawing, but for gosh sake keep the design TIN somewhere besides the design platform's DTM. I can't tell you how many times we had a project crash and could fairly quickly recreate the project by just starting a one and "TIN'ing the TIN".


Thanks all for your responses. We just created the *.dtm files in Inroads using the XML files from Civil3D. We are waiting for our client's comments. Hope they are not too bad. Thanks again!!

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