In general, Revit interacts pretty well with AutoCAD .dwg files. Things can start to get a little strange when dealing with large survey and site files, but there are workflows that will keep your Revit file and CAD links manageable (be sure to establish coordinates).

AutoCAD Civil 3D files, however, are an entirely different matter. In the past, I have noticed that sometimes certain survey dwg files would seem to split into two pieces when brought into Revit. Here is an example, where the regular AutoCAD contours and the C3D TINN have split into opposite corners of the current cad link. Even though they are both at the correct z elevation, they are in entirely different x, y locations.

It can be difficult to notice at first, because they will be miles apart, but when you hover over the link, the blue bounding box will extend much larger than it should. The left image is an unsplit link, while the middle and right are two halves of the same link (in plan).

What seems to be happening is that all of the 3D data (TINNs and COGO points) from Civil 3D “splits off” (for lack of a better term) and is locating within Revit as if the regular AutoCAD linework is at the actual origin. This is strange behavior that might be related to the fact that regular AutoCAD files (that are larger than 20 miles) will “forget” their origin once in Revit. And it seems as if the C3D data, unlike the regular data, does not.

It can be a tricky issue to spot, because when you initially link in the dwg file, everything will appear fine (the TINN is aligned in plan and the bounding box edges are all visible).

But after the dwg file is opened and saved in Civil 3D and then reloaded within Revit, the dwg link has now “split.” It is interesting to note that it is the regular linework that seems to “jump” while the TINN has remained near the Project Base Point.

There are two options for dealing with issue, depending on how much Civil 3D data the file has and how important it is to keep.

1. Explode the C3D data. This might be the best option if there is limited data (such as just a TINN) to explode.

2. Create two instances of the C3D dwg file. To do this, simply copy it and move the second copy so that the C3D data overlays correctly on the first.

This is usually the preferable option since it keeps the C3D data intact. However, you should be aware that this results in duplicate “false” data off in space, which can be confusing or problematic if a user finds this and starts working with it.

Finally, it seems like this issue only exists when the file has been recently saved within Civil 3D. But it also seems somewhat inconsistent, with various results depending on what AutoCAD it was saved in prior to being linked or reloaded. It also seems that once the link “splits” the only way to get the link to realign is to remove it entirely and start with a new link (even if the C3D data is exploded, it will remain “split”).

I would be interested to know if anyone else has encountered this issue in Revit. I have not found any indication of this elsewhere, but then again, no one else seems to be posting much about sites or landscapes in Revit.