A while back, I did a post about bringing DEM data into AutoCAD Civil 3D (you can read it HERE if you are interested). In the comments, people have asked several questions and have had some issues. One of the issues is, you have to know what coordinate system the DEM file is using. Another is that, no matter what coordinate system you are using, the DEM comes in as though the elevations where in meters (and will then convert those meters to feet).

Well, all that’s about to change. If you have the Autodesk Infrastructure Design Suite (Premium or Ultimate) then you also have Autodesk Infrastructure Modeler (AIM). You can use AIM as a DEM to Civil 3D surface converter. Simply import your DEM file into AIM, export to a .imx file, and then import that into Civil 3D.

Open up AIM and create a new project. Give it a name and a place to save it. Keep the coordinate system as LL84 (there’s no need to change it) and leave everything else the way it is.

Create a new project

Once the project is created, import the DEM file into AIM. This is done through the Data Sources panel. Expand out the different data sources and choose “Raster” as the data source. Browse to your DEM file, open it, and then Refresh the data. You will now have a beautiful surface in your model.

Import DEM as Raster

Refresh DEM

Now that the DEM is added to your model, export it out to Civil 3D via the .imx file. In the application menu of AIM (that’s the purple I in the top left corner of the application), choose the Export menu and then “Export to IMX”. In the Export to IMX dialog box, choose to export the entire model, and give it a file name. AIM will choose an appropriate coordinate system so just leave that alone. Depending on the size of the DEM file, this could take a few minutes.

Export to IMX

Once the .imx file is created, open Civil 3D. To import the .imx file, it’s important to remember to assign a coordinate system to your drawing. If you aren’t sure how to do this, click HERE. Once in Civil 3D choose the Import IMX command (it’s on the Import panel of the Home tab of the ribbon or type IMX_IMPORT at the command line). Simply browse to the .imx file and bring it in. Because both the .imx file and your drawing have coordinate systems assigned, the DEM file comes in at the correct location and at the correct elevation. You may want to change the name of the surface as well as the style but, you now have a beautiful DEM file in your drawing and you didn’t ever have to know what coordinate system it was using!

Import the .imx file into Civil 3D

And if anyone is wondering, the DEM file I used while creating this blog post created a surface in Civil 3D with almost 4 million points.

Surface Properties

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