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

So, you’ve heard that there is a lot of free data that you can use in your GIS software.  Well, some of that free data, you can also use in Civil 3D.  Civil 3D is built on top of MAP so all that free GIS data, you can use as GIS data in Civil 3D.  But, I don’t want to use it as GIS data, I want it to be Civil 3D data!  Well, if you have a DEM (Digital Elevation Model), you can add that to a surface and away you go!  Follow the link to find out more.

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If you are familiar with the coordinate systems in Civil 3D, you may be aware that the transformation tab allows you to transform a local coordinate system to a known coordinate system.  In other words, Ground (project coordinates) to Grid (known coordinates).  Now, how does this tab affect bringing survey data into the survey database?  Well, it all depends on where the data is coming from.

<begin disclaimer>I am not a surveyor nor do I pretend to be one on TV.  I’ve just learned a lot about this stuff in recent years.  I’m by nature an engineer and engineers aren’t allowed to play with survey data so everything I have, I made myself.<end disclaimer>

So what happens when you have transformations set to your drawing and you import survey data from a point file?  Well, point files typically don’t have coordinate systems assigned to them (can they ever?).  When using the import survey command, the points come into the database as if they were collected using the same coordinate system as the survey database.  Since I live in Colorado, I’ll use NAD83 Colorado State Planes, North Zone, US Foot as the coordinate system.  I create a point file that has the following points in it:

2,50016.9791,40018.2566,100.0000,GS
3,50053.5856,40023.9971,100.0000,GS
4,50068.3375,40063.0876,100.0000,GS
5,50060.6884,40110.9256,100.0000,GS
6,50012.0618,40132.2476,100.0000,GS
7,50002.7736,40084.4096,100.0000,GS
8,50036.3751,40087.9633,100.0000,GS
9,50036.1019,40056.5269,100.0000,GS
10,50082.2699,40017.9832,100.0000,GS
11,50102.7586,40075.3888,100.0000,GS
12,50104.9441,40162.5906,100.0000,GS
13,50039.9265,40165.3242,100.0000,GS
14,49981.1921,40022.0836,100.0000,GS
15,50051.4002,39978.8927,100.0000,GS

The survey database has the same coordinate system as the drawing, NAD83 Colorado State Planes, North Zone, US Foot and has a very simple transformation assigned to it.  Basically, it will translate the ground coordinate N=40,000 E=50,000 to the grid coordinate N=1,040,000 E=3,050,000. When the point file is imported into the survey database, the points are brought in and the transformation settings in the drawing are not honored.  I don’t know exactly why but, this is my theory on what is happening.  When you bring the points directly into the survey database, they don’t come into the drawing and then into the database, they are brought directly into the database from the point file bypassing the drawing altogether.  Since the point file has no coordinate system (yet alone a transformation setting), they are simply brought directly into the database.

As you can see, the points coordinate match the points in the point file and do not reflect the transformation settings.  If you need the points to honor the transformation settings, import the points into the drawing first, and then import the points into the survey database from the drawing.  Since the points are in the drawing, the settings of the drawing will be used and the points will be transformed as they are brought into the database.  In this image, you can see that the points in the drawing are in the project coordinates:

And after the points are brought into the survey database, they are in the known coordinate system:

Hopefully, this will help clarify some of the mystery of the survey database.