topic Re: My Georeferencing Coordinate System is Missing - Civil 3D in Forma for Design Forum

My Georeferencing Coordinate System is Missing - Civil 3D

Robbie_Latta — Fri, 03 Oct 2025 16:14:28 GMT

I'm trying to import a .dxf export from an existing Civil 3D .dwg. However, the coordinate system I assigned to the .dwg (EPSG:2274, NAD Tennessee State Plane Zone US Foot) is not available for selection in Forma. Why is that?

I'd like to be able to have the linework I've already drawn georeferenced in Forma in the right place.

Re: My Georeferencing Coordinate System is Missing - Civil 3D

kristoffer.dyrkorn — Fri, 10 Oct 2025 10:54:20 GMT

Hi,

I have now added this coordinate system to the list of coordinate systems we support in the import stage in Forma - see screenshot below.

Please note, that due to a limitation in the coordinate transformation library we use (we are planning to migrate to a new one), we cannot use data files (us_noaa_TN.tif or similar) in the transformation process. So for the current definition in Forma, I have used an approximation instead, with parameters defined here: https://epsg.io/2274-1515 (ie based on a Helmert transformation).

Best regards,

Kristoffer

Software Engineer,

Autodesk Forma

Re: My Georeferencing Coordinate System is Missing - Civil 3D

Robbie_Latta — Fri, 10 Oct 2025 14:34:12 GMT

It looks like it's been added to the list, but my model is coming in way off - by 593 km.

Does Civil 3D use a different approximation? Here's my Civil 3D coordinate system dialog:

Re: My Georeferencing Coordinate System is Missing - Civil 3D

kristoffer.dyrkorn — Mon, 13 Oct 2025 11:23:22 GMT

I would not expect that the approximation would introduce an offset of ~600km.

What I think happens here, is that the exported geometries have ended up with coordinates having a different origin than the origin of the coordinate system itself. Depending on which product is used when exporting, this can sometimes be default behaviour, and other times be configurable behaviour. Forma, by default, expects coordinates to have the coordinate system's origin as origin.

When doing the export, do you see any options that would allow you to set what the origin for the export should be? At times, products rely on local coordinates internally, relative to some defined reference point. I think that here, this reference point is ~600 km off the coordinate system origin, and that this is what introduces the offset when importing the data.

You could try to export data using the coordinate system's origin as the data origin, or, you could use Forma's built-in support to compensate for such offsets. If the offset values are known (shown in Civil 3D) you could manually add these values in the dialog shown in the screenshot you provided, in the X / East, Y / North fields, and then run the import. That should make things align again (pending any offsets that would be introduced by the approximation).

Best regards,

Kristoffer