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I have some survey data exported from Civil 3D in both dtm and dem formats. I thought the I would be able to use the dem more easily, but I think the format is different from a USGS DEM. Is it possible to use this data in either ArcMap or QGIS? I'm using QGIS for raster analysis with the GRASS plugin as I don't have the 3D Analyst extension.

Thanks for any help!

@johanvdw Thanks guys, here it is. Starts with 'Autodesk Export Surface2DEM' then

{1 2 405 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 0.000000000000000D+00 1 1 4 0.585166731876923D+07 0.212104288166666D+07 0.585166731876923D+07 0.212938888166666D+07 }

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Try posting the first lines of the DEM file here, it will give an idea which procedure you can use to load the file. – johanvdw Jan 17 at 19:13
@johanvdw- I'm actually able to open the DEM in ArcMap, and have tried to convert it to a Geotiff to use in QGIS but that hasn't worked. I'm unable to open directly in QGIS. Sorry, I'm not sure how to post the lines, can you advise? – Erin Jan 17 at 20:03
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open the file with a text-editor such as notepad – johanvdw Jan 17 at 21:00
try to open with notepad or wordpad, and copy just a few of the top lines – Brad Nesom Jan 17 at 21:01

2 Answers

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In Civil3d (2010+), you can choose GeoTiff as an export option, then load into QGIS (1.8) as a regular old raster, create a hillshade etc.

They make you choose this in the 'Dem file name' option in the export surface dialog so it's not immediately obvious where to change formats.

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@WolfOdrade- This is really useful, thanks. The file was exported by someone else so I'll see if they can send me a geotiff. – Erin Jan 20 at 7:22
up vote 1 down vote

In Autocad Civil there's no .DTM format, sir, only a .TIN one.

You can easily convert a C3D surface to Dem (readable by Qgis) by means of the _SurfaceExportToDem command.

:)

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The file was exported by someone else for my use so I'm not sure what process they used. It just seemed that the DEM may need conversion or some processing as I was having trouble getting it to load or render. – Erin Jan 20 at 7:19

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