IMPORTING 3D CAD FILES

HOW TO IMPORT 3D CAD

Use Insert > Link CAD or Insert > Import CAD.

In the Insert CAD dialog box:

• untick Current view only (this allows 3D data in CAD files)

• Positioning: should be Auto - Center to Center unless you definitely know the origin in the CAD file matches the Revit file.

• Place at: is the level the CAD will be located. Check it is correct.

• Tick Orient to View.

• Go through the other options and make choices.

• Select the CAD file

• Hit Open.

NOTE:

• If you tick Current view only all 3D data in the CAD file will be flattened to 2D.

• if you use Positioning: Auto - Origin to Origin and the CAD file's world origin (Revit only reads the World UCS) is further than 20 miles away

• ALL THE 3D VIEWS IN THE PROJECT WILL BECOME BLANK. (not actually blank, but the model will be so small you can't see or find it.)

  • To fix this is a nightmare SO DON'T DO IT. Refer to HELP > 3D VIEWS ARE BLANK on how to fix this problem.

• If Orient to View is ticked and the view's orientation is True North the CAD file will come in oriented to True North. If Orient to View is unticked it will be orientated to Project North. Note that if you change the orientation of the view after placing the CAD file, the CAD file will rotate itself upon any Reload.

• It is best practice to nominate the Import units, as Auto-Detect doesn't always work, especially if the CAD doesn't comes directly from AutoCAD (DWG) or from Microstation (DGN).

• Correct lines that are slightly off axis straightens lines that are less than 0.1 degree off axis (Project North axis). Untick this if importing survey CAD files.

3D GEOMETRY

CAD files with 3D meshes can be imported a 3D geometry into Revit.

In Revit you have to import or link a 3D CAD file into a family, usually Generic Model, or Mass if you want to use it to host walls, roofs etc. If you will need to scale your import use the Planting category. It can be a separate family (.rfa) file, or within the project as an in-place family. Putting the import within a cuttable family (don't use Furniture or Plumbing Fixtures for example) ensures the import will be cut by plans and sections. If you don’t do this the import will always display in elevation.

Keep in mind that an import in Revit is just a dumb object. You can’t do anything with it except look at it. You can’t snap to it in 3D, alter it in any way and only change its appearance in very limited ways. Although it can be cut in plan and section the results are not very good because what is being cut are usually isolated thin planes.

SURVEY 3D INFORMATION

Survey 3D information is used to create Toposurfaces. There is no need to put 3D survey CAD files into families.

As noted above untick Correct lines that are slightly off axis when inserting a survey CAD file.

It is important to take note of the Orientation of the view you are placing a CAD file.

Revit remembers which orientation - Project North or True North - was set in the view when the CAD file was placed.

If the orientation is changed from that original value, when the CAD file is Reloaded it will rotate itself.

And it is only the original view that matters. Changing orientation of other views where the CAD file is visible makes no difference.

(To fix a rotated view change the orientation of the view the CAD was originally placed in back to its original orientation and Reload again.)

Because of this it is best to place a CAD file in a view that is unlikely to have its orientation changed.

Or better still create a working view just for placing 3D CAD files so you know which view has been used for placing CAD files.