Revit Architecture: Shared Coordinates (Still) Help Achieve Project Success
In December 2015, I wrote an article for AUGIWORLD titled Shared Coordinates and Civil State Plane Coordinates which highlighted the power of using shared coordinates and alignment with actual state plane coordinates in Autodesk® Revit®. I also explained how to use shared coordinates with CAD civil files to enhance workflows with the civil engineering members of a project team. Over the last decade, Revit has rolled out numerous new tools and features. That’s why I’m back to share a simplified, updated workflow for working with shared coordinates because none of those new tools help us with this. Maybe except for one.
Back to the Basics
“Shared coordinates” is a BIM buzzword, and many people struggle to understand how they function on a project. Here’s the lowdown: within the Revit environment, shared coordinates use geolocation to ensure alignment of multiple models—either between Revit models only or between Revit models and AutoCAD site/civil content—when they enter the building coordination model (BCM) environment.
A BCM is a host file used for virtual cross-checking between various design team disciplines and understanding the building’s relationship to true north. When setting up a BCM, the main goal is to create a Revit environment that uses a civil drawing as the model’s underlay and locate the building on the site. Shared coordinates are exclusive to the BCM, in this workflow, and are not present in linked models, such as the architectural scope model. The exception is when exporting models to CAD using shared coordinates, which must be done from the BCM using linked views.
Consultants are often asked to set up specific views to be used in the BCM to export. To establish those views, every consultant model is required to be linked and located in the BCM, aligned over the correctly placed architectural model. By restricting shared coordinates to the BCM, teams can link all scope models to each other using “origin to origin,” preventing shared coordinates from breaking between scope models throughout the life cycle of the project.
Getting Started
At the beginning of a project, the architectural model should be linked into the BCM. To set the coordinates in the BIM environment, the civil engineer must provide the architect with two points to set the survey and project base points. The chosen points require northing/easting coordinates and elevation and should be from permanent real-world features that will remain post-project—not items that may be removed during the design process. For example, a property corner or benchmark outside the work area is recommended. Additionally, True North needs to be illustrated to align it in the Revit model, showing the difference from Project North, which is always upward in view.
After the engineer establishes the initial building location, the architect should provide a clear building footprint, exported to DWG for the civil site engineer. Then, discipline models can be compiled and positioned in the BCM—over the architectural model—using gridlines. All subsequent exports from consultants' files must be executed from the BCM.
Step-by-Step Guide to Setting Up Shared Coordinates
Setting up your BCM
1. Create a BCM file from a new model and save it to the folder where the scope model is saved.
2. Change the project units to “feet” and rounding to “custom,” and type “0.0001” as the rounding increment
3. Choose the view for the site plan and make sure the orientation is set to “True North.”
4. Link the cleaned version of the civil CAD plan to the BCM, center to center. Make sure the civil file is North and East of the Revit origin point in the BCM.
5. Link the architectural model(s) to the BCM, origin to origin.
6. Unclip the project base point and survey point; move the survey point to the first reference point on the plan.
7. Move the project base point to the second reference point on the plan.
Importing Shared Coordinates
8. Link architectural Revit model to the BCM and align it to the building footprint in the linked civil file. The model may need to be rotated to align with the civil file.
9. Using model lines, draw a circle around the two reference points. These will need to be exported in a CAD file for testing purposes and should remain in Revit for reference.
10. Use the “shared reference point” tool located on the “add-ins” tab to import the shared coordinates from the XML file.
On the bottom left corner of the Revit window, the prompt "Select ORIGIN point to align to" will appear. Select reference point 1.
Next, the prompt "Select a Point on +Y (Up) Direction to align to" will appear. Select reference point 2. Make sure to select the exact point or intersection of the two points—otherwise, the coordinates will be off. When a dialog box appears, select the XML file provided by the civil engineer.
Select yes, then click “ok.”
11. From the “manage” tab, select “location” and fill in the project address. Then, select the “site” tab and pick the name that corresponds with the XML file and make current.
Verifying Coordinates in Revit
12. Select the survey point (triangle) and review the properties information under “identity data.” The N/S value and the E/W value should match the northing and easting from the civil file.
13. Verify the northing and easting at your project basepoint where reference point 2 is located.
14. Switch to an elevation view and align the model level with the matching survey point elevation.
15. If everything is correct, attach and pin the paperclip to the project basepoint and survey point.
Exporting back to CAD for final verification and Civil use
16. To verify you’ve done this correctly go to File > Export > CAD Export > DWG. This should export the site view used to bring everything in with the civil plan.
17. Select the "…" button to access the “modify DWG/DXF export setup” settings.
18. Select the “Units & Coordinates” tab and change the defaults to “foot” and “shared,” then click “ok.”
19. On the DWG export dialog, select “next.”
20. Uncheck the box that says “export views on sheets and links as external references” and save the CAD file to your project folder.
Verifying Coordinates in AutoCAD
21. In AutoCAD, open the file you just exported to verify the position.
22. Type “units” and set the length type to “decimal”, set precision to “0.0000” and set the insertion scale to “feet.”
23. From the exported site view, select one of the circles around the reference points and then review the geometry section of the properties under “Center X (Northing) Center Y (Easting).” They should match the Civil file. If they do not match, review the previous steps.
All Other Revit Disciplines
Pro Tip: Prior to starting these steps, have your consultant set up a view, or views, with the objects needed for civil coordination—including grid lines—so you can align their model to yours. The, set the visibility graphics to “by linked view” to export what is needed and enable consultants to show what they intend to coordinate with civil.
24. Open the Building Coordination Model.
25. From the site plan view, link the consultant model to the file using “manual center” for the position option and place the model near the architectural model.
26. Position the consultant model using some predetermined reference marks, like column grids, to align the models.
27. Insert other consultant models as needed using the previous steps.
28. Duplicate the site view for each CAD file you need to export. This isn’t required each time, only for each type of export needed. (i.e. foundation, plumbing, architectural footprint.)
In conclusion, shared coordinates are a powerful tool in Autodesk® Revit®, allowing for alignment of multiple models within the Building Coordination Model (BCM) environment. By following the steps outlined above, architects and civil engineers can better collaborate and elevate their design solutions.
