Join Paul F. Aubin for an in-depth discussion in this video Linking AutoCAD DWG files, part of Revit 2018: Essential Training for Architecture (Metric).
- [Instructor] It's fairly common for you to need to access files created in other CAD formats from time to time within your Revit projects. Now one of the best ways to do that is to actually use the Link CAD feature. So with Link CAD, we'll be able to reference the external CAD file created in other programs like AutoCAD or MicroStation and that file will be linked into Revit as an object. If that original file changes, we'll be able to refresh that link and capture those changes. So let's go ahead and walk through the process here. So it starts on the Insert tab with the Link CAD button.
So what I'm going to do here, is select this file called AutoCAD Floorplan; I'm going to single-click on it. You'll get a preview of it over here and you get a series of options down at the bottom. Now, there are several settings down at the bottom. We can decide how we want the colors coming in from the CAD file to be interpreted. I like to invert those colors because AutoCAD is on a black background and most of it's colors are optimized for that and Revit's on a white background so if you invert them they usually display better on the Revit side of things.
As far as layers go, it's possible to specify certain layers but I think it's usually a pretty good idea to just bring in all of the layers from the CAD file. Likewise, with units, Revit can Auto Detect the units which usually does the right thing, but if for some reason the file comes in too big or too small, you can just undo and then figure out what unit it should be and choose it directly off the list, but usually Auto Detect will give you good results. With a small file like this that's mostly rectilinear, Correct lines that are slightly off axis is a pretty good setting to enable.
This will correct any inaccuracies in the file. If the file is very large, meaning geographically large, like several kilometers and so on and maybe it represents a site plan with a lot of irregular geometry, than Correct lines off axis might distort the file and reduce the accuracy, so you might want to uncheck it in those cases. Now as far as Positioning goes, there are several choices but usually, you're going to try Origin to Origin and see what you get. If for some reason, the file comes in way off screen or at some unusual location, you can just simply move it to where you need it to go, but let's start with Origin to Origin and see what happens there.
Now this checkbox over here on the left is fairly important, because if you uncheck it, what you're doing is telling the CAD file to behave like model geometry. So even though it might be 2D line work within that CAD file, it will show in all Views, 2D Views, 3D Views, and so on, as if it was actually drawn on the ground. If you check this box, than instead, it will interpret this CAD geometry coming in as View specific elements and in this case, I'm bringing it in to the Level 1 Floor Plan, so it will only exist in that Level 1 View, it won't show anywhere else.
So in this case, I'm going to choose Current View Only, because when I open this my intention for this CAD file is I want to actually trace over it with Revit geometry. Now, when it first comes in, you'll see it kind of come in in the middle of the screen. If you kind of think about where the center is between these elevation marks, that's about where Revit's origin is and you can see that the lower left-hand corner of the CAD file was the corresponding point in AutoCAD, so that makes a certain amount of sense, but if for some reason you didn't like where that was positioned, you could actually move the file.
Now, in order to move the file, you would have to select it. If you highlight it and nothing happens, you don't see an outline, or if you try and click it, and you're not able to select it, than there are two selection settings that you need to look at in order to make it selectable. If you come over here, right below the Modify tool, and click the drop-down, there are a series of check marks that are available. You need to make sure that both Select links, and Select pinned elements are enabled. If either of these is unchecked, you will not be able to select or highlight this file.
So that is because this is a link file, so that first one is controlling whether you can select links and it is currently pinned, so when I select it, notice that there's a push pin on this file. The reason it's pinned is to prevent you from accidentally moving it. So when you bring in a file Origin to Origin, Revit automatically pins it. So if you decide you do want to move it, unpin it first, and then you can move it. So I'm going to undo that, and I will repin. So now I'm going to zoom in and what I want to do is, start tracing over this file.
There isn't any way to automatically convert a CAD file into Revit geometry, so, the next best thing is to trace over it, but it turns out tracing over it is fairly simple to do and goes fairly quickly. So I'm going to go to the Architecture tab, click the Wall button, and I'm going to choose the generic 300 millimeter wall. Now, you are able to snap to any of the geometry within the file, it'll find endpoints, it'll find midpoints and so on, but notice that if you put your mouse between two parallel lines, it also senses where the center is between those parallel lines, making it very easy for you to trace over this CAD file.
So I'm going to trace those two thick walls with generic 300 millimeter, press Esc one time, change to the 79 millimeter partition next and begin tracing over some of these others. Now I'm going to Esc in between, let me zoom in a little closer, and notice that I'm actually drawing just partial length here. Now I'm doing that on purpose because if you get too close to the ends here, it might snap to the wrong thing, so it's a lot easier to use that center snap if you stay away from other geometry.
But then it turns out, it's really easy to clean that up with the Trim and Extend tools. So if I go to Modify, I'm going to use Trim/Extend Multiple Elements. Now this command allows me to select a boundary edge first and then either extend or trim multiple elements to that boundary edge. So I'll start with this exterior wall here, and make that my first boundary edge, doesn't matter if you click it at the center or the edge, you'll get the same result, and then I'm going to extend this wall and this wall. Now I want to reset the boundary edge.
Just click an empty space to do that and pick your next boundary edge. So here I'm going to pick this one, and you can even use a crossing selection to select multiple elements to extend at the same time. Now the boundary edge is still active so you could further select other elements as well. Once again, click an empty space when you're ready to continue, pick a new boundary edge, and extend additional elements. Now I don't want this wall here, so I'm actually going to trim it off. The boundary edge is still active, so just remember to pick the side you want to keep.
So as long as I pick that lower portion, it'll trim that line back. Now I'm going to cancel all the way out of that command, and next add a couple doors. So notice that I did draw the walls right through the doorways and that's because obviously when we place Revit doors, they will automatically cut holes in the wall geometry. So that's the way that you're going to want to build your Revit file on top of this CAD file. Now that's enough geometry for us to get the general idea of how the process works. Now what I want to show you is if I go to any other View, such as a 3D View, spin this thing around, I'm seeing the Revit geometry in all Views, just like you would expect, but notice that there is no CAD geometry displaying here.
That's because I chose that Current View Only checkbox when we first brought it in. So I'm limiting the display of that CAD file only to the Level 1 Floor Plan. Now let me go back to Level 1 one more time, we've zoomed back out here, and let's say that the owner of this CAD file has made a change. So I want to capture that change here in my project and make the update. So to do that, you go to Insert and then Manage Links. Here you've got tabs across the top for the different kinds of files that we can link, click the CAD Formats link, select your AutoCAD Floorplan and then at the bottom are a series of buttons; we could Reload the file, Unload the file, Remove the file.
Now, if the file that was updated was overwritten and placed in the same location, we could just simply reload it, but in this case, the new file that we got from the author has a slightly different name, so I'm going to click Reload From instead, and point to this version of the file, AutoCAD Updated, click Open and then OK, and you'll see that the left-hand side of the plan has adjusted slightly. Now notice also that the Revit geometry does not adjust so this is pretty important because even though you traced over it, that does not automatically keep those things connected.
So I'm going to select the affected geometry in my Revit model, go to my Move command, and I'm going to move that over to the new location. So anytime that you're working with someone who's building files in other formats, you can link those formats in, like your CAD files from AutoCAD or DGN, and then use those for reference in creating your corresponding Revit geometry.
Paul also shows advanced techniques for modeling stairs, complex walls, and partially obscured building elements, as well as adding rooms and solid geometry. Finally, discover how to annotate your drawing so all the components are perfectly understood, and learn how to output sheets to DWF, PDF, or AutoCAD.
- Understanding BIM and the Revit element hierarchy
- Navigating views
- Creating a new project from a template
- Adding walls, doors, and windows
- Adding plumbing fixtures and other components
- Linking AutoCAD DWG files
- Rotating and aligning Revit links
- Working with footprint and extrusion roofs
- Adding openings
- Adding railings and extensions to stairs
- Creating stacked and curtain walls
- Hiding and isolating objects
- Adding rooms
- Creating schedule views and tags
- Adding text and dimensions
- Creating new families
- Using reference planes, parameters, and constraints
- Plotting and creating a PDF