Dec 08
31
Shared Coordinates in Revit (and AutoCAD)
One feature of Revit that has confused me for quite some time is Shared Coordinates. If you don’t know what this is, basically, if you have a drawing in AutoCAD at specific coordinates, you can not only bring the drawing into Revit, but you can also bring in the coordinate system. This is really helpful when you’ve received, for example, a topography drawing from a surveyor which locates the contours at their actual coordinates in the world. The trouble comes in when those coordinates are so gigantic that when you try to bring it into Revit, at those same coordinates (“origin to origin”), you get an error message that basically says that since the numbers are so large, the drawing will just be brought in at the “center”. If we were working in AutoCAD, the solution would be to move the drawing closer to the origin. Well, in Revit, there isn’t an origin…OR IS THERE?? If you draw two lines, in AutoCAD, that cross each other at the origin, and then import it into Revit, you’ll see where the origin is. If you do a “spot elevation,” in Revit at that crossing point, you will see the value as, N 0″, E 0″ (fig. 1).
Figure 1 – The Origin in Revit |
Figure 2 – Rotated Building |
When you’re ready to import the DWG file into Revit (File –> Import/Link –> CAD Formats), within the Import/Link CAD Formats dialog box, in addition to selecting the Link option, next to where it says Positioning (to the bottom-right), choose Manual – Center. Click somewhere close to the origin to place it. Then, using the Move command, move the drawing from any point you’d like the origin to be to the origin we just located. If you are importing a building, it’s a good idea to rotate it so that one (or more) of the walls a perpendicular (fig. 2).
Now that we’ve brought the DWG file in, we need to bring in the coordinate system as well. Click Tools –> Shared Coordinates –> Acquire Coordinates then, select the imported DWG file. Now you’ll notice that the values of the spot elevation have changed to reflect the new coordinate system (fig. 3).
Figure 3 – Acquired Coordinate System |
One other thing worth mentioning is the fact that right now, we’re looking at our plan view in an orientation of Project North. This allows us to view our building orthagonally. If we’d like to view it at True North (meaning North points straight up), we need to go into the View Properties (right-click in the view and select View Properties) and within the Graphic group, next to Orientation, click the pull-down menu and choose True North. After you click ok, the view will change. To lock the DWG file, and make sure it changes with the orientation change of North, select it and click the blue push pin icon: 
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This is a confusing topic so please email me at scott@caduzer.com if you have any questions.
