The coordinate systems used by Autodesk Revit and AutoCAD Civil 3D are very different. Revit uses a coordinate system relative to the building faces and Civil 3D uses an established coordinate system relative to the surface of the earth.
Since both coordinate systems are unrelated, collaborating in the past has been very tedious and usually boiled down to the Revit user having to manage the location of the project point relative to the survey point. And if the building’s position had to change its position relative to the earth’s surface, it had rippling effects in Revit. Autodesk has released an extension that makes this process easier. This extension can be downloaded from the subscription site in the Revit entitlements.
To implement this extension, download and install it on all Revit and Civil 3D systems. If Revit and Civil 3D are on the same system, it only needs to be installed once.
The way the process usually kicks off is by exporting a DWG file from Revit defining the building footprint. This drawing is referenced into the Civil 3D site file and is moved and rotated until it is in the correct location relative to the surface of the earth.
Next, in Civil 3D, the Export Shared Reference Points tool which is accessed on the Tool Palettes > Toolbox tab in the Miscellaneous Utilities category under Shared Reference Point is run by right-clicking and selecting Execute.
There will be a prompt at the command line: Select ORIGIN Point. This is typically a building corner. Usually, the bottom left corner is a convenient point to use, but this point should be coordinated with the Architect to make sure all parties involved are using the same information. Once that point is clicked, there will be another prompt at the command line: Select a Point on +Y Axis. What is being defined here is the direction of the north elevation view in the Revit model relative to the origin point. Once defined, the Select Units and Confirm dialog opens. Since this tool does not read the units of this drawing, the units must be selected in the dialog. Click OK to proceed.
The Save As dialog opens. Browse to an appropriate location like the project folder in which to save this XML file. This file will be imported into the Revit file to establish the building origin and north rotation for site drawings. Click Save to finish.
Once this file is available, the file must be imported to establish the location of the Project Base Point. This is done from the Add-Ins tab of the ribbon. Click the Import Shared Coordinates from XML File tool.
You will be prompted: Select ORIGIN Point to Align To. This will be the same point on the building that was defined in Civil 3D. After picking this point, the prompt will read: Select a Point On +Y (Up) Direction to Align To. This is the direction of the north elevation relative to the origin point. After clicking, the Open dialog appears. Browse to the location of the XML file delivered from Civil 3D, select it, and click Open.
A dialog appears asking if you are sure. Click Yes to verify.
Another dialog opens to say you were successful. Click OK to dismiss.
There is one more thing to do to finish this set up. Go to the Manage tab of the ribbon and click Location on the Project Location panel.
The Location and Site dialog will open. Make the Site tab in the dialog current, click the site named after the XML file, and then click Make Current to use the site definition from the XML file. Click OK to finish.
Now that your project point and north arrow rotation has been established, you can link DWG files from this coordinate system into the Revit model with no manipulation or transformation. In the Link CAD Formats dialog, just make sure that Positioning is set to Auto – By Shared Coordinates and clear out the checkbox for Orient to View. Click Open.
A dialog appears stating that the link’s world coordinates will be aligned with this project’s shared coordinates. Click Close to dismiss.
The DWG file will drop in using the correct coordinates and rotation. Note that it may be necessary to use the Export Civil 3D Drawing command to convert Civil 3D objects to linework so that they can be displayed in Revit.
This setup also lets the Revit user export drawings from the model on a coordinate system that will align with the site work. After executing File > Export > CAD Formats, click the DWG option to open the DWG Export dialog. Click the ellipsis and in the Modify DWG/DXF Export Setup dialog, and on the Units & Coordinates tab, select Shared Coordinates as the Coordinate Base settings. Click OK to close and then Next to finish. Browse to a location in the project folder to save the exported file. This file can now be referenced into the site file without the need to manipulate or transform the coordinates in any way.
Using the Shared Reference Point extension helps to simplify what has been a tedious process in the past ensuring that collaboration between site and building go smoothly.
