You’ve heard the saying, “Smile, and the whole world smiles with you.” Wouldn’t it be nice if there were a BIM version of that saying? “Use BIM, and the whole world uses BIM with you.”
Unfortunately, getting clients and consultants on board with Revit takes more than just a smile. But even if your design partners are sending you DWG files instead of RVT, you can still use them in your projects for coordination. Here are three steps to getting your DWG and RVT files to work together.
Step 1: Prepare Your DWG Files.
There are a few steps I always like to take when I get a DWG file from a client or consultant. They haven’t really changed thanks to BIM—file cleanup is still good practice.
For each DWG file:
- Open the file in AutoCAD.
- Check for xrefs (externally referenced DWG files). If there are some, bind them to the drawing, using the Insert option to prevent redundant layers.
- Run SETBYLAYER. This command removes any color, linetype, or lineweight overrides from objects.
- Run PURGE. This command removes any unused layers, linetypes, blocks, and styles.
- Freeze any layers you don’t need.
- Use SAVEAS to save a copy of the file in your “CAD Links” folder (or wherever your standard linked file location is).
Step 6 is very important in this process. I always make sure I have an unmodified copy of whatever files I receive, in case something looks funny later and I want to check it against the original.
When you bring a DWG file into Revit, you have a choice between linking and importing. However, I don’t think I’ve ever imported a CAD file into Revit—there are just so many good reasons not to.
- You Can Update a Linked File. If your client sends you a new version of a DWG file you have linked into your Revit model, you have to run the Step 1 procedures on it, but as long as you don’t change the file name, you can simply replace the old version with the new. The next time you open your Revit file, the new DWG file will load automatically.
- Linking Doesn’t Bring in Any Junk. If you import a CAD file into Revit, you can explode it. Long-time AutoCAD users know the trouble this can cause in that program, and it’s no different here. In Revit, exploded imports are technically converted into Revit elements…except the “elements” are detail lines with odd names and properties mapped from the AutoCAD layers.
That’s only two reasons, but that’s enough for me. Live updating plus a clean Revit file means I choose linking every time.
Step 2: Link in the DWG Files.
We’ve established that you want to link your files, not import them. But that’s not the only choice you have to make.
First, in Revit, open the view where you want to place the CAD file. Then go to the Insert tab and choose Link CAD.
Browse to your file, and before you click on OK, check out the settings at the bottom of the dialog.
- Colors. Which option you choose here depends on your end use for the linked file. If it’s just for coordination, you might use “Preserve” to help distinguish layers by color. But if you’re planning on printing it, and because many CAD standards are set up to look good on black screens, and Revit uses white by default, “Black-and-White” may be easier to see.
- Layers/Levels. Choosing “Visible” here tells Revit to ignore off or frozen layers. (Remember freezing the extra layers back in Step 1?) Just know that if you later want to see something on one of those invisible layers, you’ll need to delete the link and relink it. If you choose “All,” you can still control the visibility of the layer through the Visibility Graphics dialog.
- Import Units. Use this setting if you want to tell Revit specifically what units the DWG file was created in. Auto-Detect usually works fine, as long as the whole team is agreed on imperial or metric units.
- Correct Lines That Are Slightly Off Axis. This option helps Revit create orthogonal geometry, preventing errors later on. It may not be helpful for site plans, though.
- Positioning. This option is more relevant when you’re linking in Revit files. CAD files and Revit files don’t often share the same coordinate system (although they can), so most of the time I just use “Center-to-Center” and manually reposition the link once it’s in. (And then I pin it so it can’t move.)
There’s also a checkbox for “Current View Only.” This means that the DWG link will only show in this view, not in other views that happen to show the same level, grid, or plane. Its advantage is that it provides more control over the file display after it is imported. Files that are linked into the current view have an option for “Draw Layer” in their Properties palette that enables you to set it to the background, where it won’t cover up items you might add later. Checking Current View Only also disables the “Place at” and “Orient to View” options—otherwise, you have to choose which level to associate the DWG to.
You can still use a linked file in other views even if you choose Current View Only during the import. Simply copy the link instance in one view to the clipboard and use “Paste–>Aligned to Same Place” in the other views.
Step 3: Manage Your Links.
Even though a DWG file is essentially static when linked into Revit (you can’t actually edit its objects), there are still a few ways you can manipulate it.
First, the Visibility Graphics dialog has a tab for Imported Categories. Each DWG file is listed here, and you can turn layers on and off as needed.
The Manage Links dialog provides options for locating and updating the file. “Status” tells you whether a file is loaded, unloaded, or not found. The “Positions Not Saved” column is related to shared coordinates, which again probably won’t apply to CAD files. “Size” is self-explanatory. “Saved Path” tells you where the file is currently located, and “Path Type” says whether that path is absolute or relative to the Revit file’s current location. (“Relative” is almost always a safer bet.)
There are also a few actions you can take here:
- Use “Reload” and “Reload From” if you get a new version of a CAD link and don’t want to close and reopen your Revit project to save the changes.
- “Unload” removes a file from all views, but not from the project.
- “Import” breaks the link and binds the DWG to the Revit file. (As noted above, this is probably not a good idea.
- “Remove” gets rid of the file completely, when you don’t need it anymore.