In today's post I will cover my preferred workflow to set up shared coordinates in Autodesk Revit, supporting roundtripping with Civil CAD (using AutoCAD or Civil 3D). There are always exceptions and situations that require deviations, but the process works well and checks a lot of boxes.
I created a detailed YouTube video highlighting all the steps, including how to move the building once shared coordinates has been enabled.
Two Coordinate Systems
Revit has two coordinate systems; Project and Survey. The process outlined in this post has nothing to do with the Project coordinate system, or project base point. In a sense, you can think of project as fake, and survey as real-world.
For example:
Project
- Level 1 being 0'-0" or 100'-0" is made up, and only relates to the project
- Spot Coordinate: N: 1'-0", E: 1'-0" only relates to the project
Survey
- Level 1 being 694'-3" relates to sea-level and is provided by the civil engineer
- Spot Coordinate: N: 1004.245', E: 745.426' relates to the state/country coordinate system
Wait for the Civil CAD file
I recommend shared coordinates start with the civil CAD file. So, wait for your civil engineer to provide a properly geo-referenced CAD file. It can just be the existing condition, but should be properly positioned for the coordinate system and for true north. Any future proposed work will just fall into place when everything is set up properly.
Tip: If civil is using Civil 3D, ask them to use the special 'Export to CAD' command to export the 3D model to simplified AutoCAD elements.
On a related note, if using this file to create a toposurface in Revit, ask for the surface to be triangulated as you get more detail that with individual polylines. However, a published Civil 3D model to BIM 360 is better, see more on that here: Site Collaboration with Civil 3D
Files required
The process involves the following files.
- Civil CAD file
- Revit Site
- Revit Building(s)
Each building should be its own model and there should always be a separate Revit site model.
Related TIP: For multi-building projects with common details, check out PARALLAXTEAM's Linked Details for Revit tool as an option to keep them consistent across all Revit projects.
BIM 360 Design Limitation
Since BIM 360 Design does not support publishing shared coordinates, and only Revit 2021 has the ability to reset shared coordinates, they are excluded from this workflow... resulting in a workflow that works most often.
Start in the Revit site model
In the Revit site model, do the following:
- Link in the Civil CAD file
- FYI: I added a large circle at 0,0 in the CAD file
- Move the CAD file near the Revit origin
- See first image below
- Notice the survey point is at the Revit origin
- Acquire the coordinates for the selected Civil CAD file
- See second image below
- Notice the survey point moved to align with the CAD origin
Tip: this Revit site file is always oriented for true north.
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| Revit site model: Civil CAD file repositioned near Revit's origin |
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| Revit site model: Coordinates acquired from Civil CAD file |
Notice the survey point, in the Revit Site model (previous image,) moved to align with the origin of the Civil CAD file. Because the origin of the Civil CAD file corresponds to the benchmark of the county/state coordinate system, so too will any references in Revit which are based on the survey point. Thus, you can get accurate Northing/Easting points and sea level elevations within any of your Revit models.
In the architectural building model(s)
Once the Revit site model is set up properly, it can be linked in to your building model(s). With that link moved and rotated relative to your building model, select the linked Revit site model and acquire its coordinates. The Revit site model can be unlinked at this point, if not needed in the building model.
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| Building model: Coordinates acquired from linked Revit site model |
Now, if you go into the Revit site model, and link the building model using By Shared Coordinates it will drop into the correct location.
Consultants (Struct, MEP, etc.) can link in the architectural model, properly position it and then acquire coordinates. No need to link in the Revit site model... but, if/when the site is needed it will drop into the correct place if linked using By Shared Coordinates.
Export geo-referenced CAD file for civil
We often share the 2D plans with civil so they can plan for stoops, walks, and drives around the perimeter of the building. If the floor plan is exported with shared coordinates, which is an option in the DWG export settings, the civil engineers can xref the file into the correct location automatically as shown in the image below!
Moving the building after shared coordinates have been enabled
You just select everything in your building model and use the move tool. JUST KIDDING! Never do that, please! :)
In the building model(s) just select the Survey Point and move it (clipped). Open the Revit site model and the building is re-located. Nothing needs to be done in the Revit site model. See the video for more on this.
YouTube Video
Here is a 20 minute video I created covering this workflow.
Have thoughts on this? Please share them in the comments section below.
Additional Posts
Here are a few addition posts on this topic, that followed this one:
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