Model Coordination Training
This month the topic for AUGIWORLD is training. There are essentially three ways that people learn: visually, auditory, and the hands-on approach. Based on those three learning characteristics there are many ways to deliver the training as an instructor. My preferred method is hands-on during a real project—people tend to retain more of what they learn when they apply it directly to their project.
After the hands-on training I like to provide the client with a series of short topic-based videos that matches up with their workflow. This gives them a library of videos they can pull from to help them along when they hit a roadblock.
In this article I will take on the topic of model coordination. I have sat in on classes for this very topic at BIM workshops, AU, and RTC. Some instructors make it more confusing than it has to be. I hope to simplify this process in a step-by-step tutorial. Unfortunately, if you are the type of person who learns best from hearing (auditory) then this may not work for you. But the visual and hands-on people should be all set!
The Points
Revit has two points it works off of during model coordination—a project base point and a survey point. These can both be turned on from your visibility graphics.
Figure 1: Project base point and survey point in Visibility Graphics
Both the Survey point and the Project base point can be clipped or unclipped. It is important to understand that when you move these points they affect your project differently depending on whether the point has been clipped or not. Figure 2 shows the graphic of a project base point. The top image is a project base point that is clipped, and the bottom image is the project base point unclipped.
Figure 2: Project base point
The Coordinates
When you move a project base point that is clipped, your project coordinates will change as well. Figure 3 below shows a clipped project base point that has been moved two feet to the right (East). Moving a clipped project base point is the same as using the relocate project tool found in the Manage ribbon on the Settings panel.
Figure 3: Moving a clipped project base point
Moving a project base point that is not clipped repositions the overall project coordinates, but not the coordinates of the model elements. Figure 4 shows that the spot coordinate does not change when the unclipped project base point is moved two feet to the right (east.).
Figure 4: Moving an unclipped project base point
When you move a survey point that is clipped, you will see in Figure 5 that the survey reference point does not change, but the relative distance of model elements from the survey point do change.
Figure 5: Moving a clipped survey point
When you move a survey point that is unclipped, you will see in Figure 6 that only the survey reference point changes, but the coordinates of model elements do not change.
Figure 6: Moving an unclipped survey point
Revit – Revit File Linking
Directly linking a Revit model into another Revit model is relatively straightforward. Make sure your survey point and your project base point are in the same location in both models and then link using origin to origin. Autodesk got it right when it made origin to origin the default in the 2016 release! Figure 7 is a basic example showing a Revit Structural model linked into a Revit Architectural model. Both models have the survey point and project base point in the same location.
Figure 7: Revit to Revit link
Revit – CAD File Linking
Next we will look at linking a CAD (dwg) file into Revit for drawing coordination. Most often you may be provided with a Civil model showing the property and building location for your project, and coordination is needed in both directions. The Civil firm provides the Structural firm with a CAD (dwg) based site plan and the Structural firm may need to export their model into a CAD (dwg) format to the Civil firm.
Based on what we learned in the coordinate section of this article we can assume that the project base point is relative to the survey base point. Revit also refers to the survey point as a “shared site” point. Figure 8 shows a CAD file site plan with three buildings located on it. Every point in the AutoCAD file is relative to world coordinate system point x=0, y=0. In Revit our project base point is relative to the survey point or “shared site” point.
Figure 8: Base site plan from AutoCAD
When linking the Civil CAD (dwg) file into Revit, use the Auto -Shared Coordinates option. When you do this Revit will warn you that the files have different coordinate systems and that Revit will align AutoCAD’s world coordinate system with Revit’s shared coordinate system. The result is perfect—the CAD file is placed in the correct location inside of Revit.
Figure 9: Auto - Shared coordinates option
Figure 10: CAD result linked into Revit
When exporting the Revit model to a dwg format for use by the Civil firm, make sure you set your dwg export setting to use shared coordinates.
Figure 11: dwg export setting
When the Civil firm externally references the dwg file you provided from Revit it will land exactly on the site where it was intended to be placed.
Summary
Learning is best retained when taken in small bites. There are so many other subtopics to cover with coordinates inside of Revit. The purpose of this article was to give you a clear understanding of the survey point and project base point inside of Revit and I am hopeful it did that. You should also be able to coordinate a building using different Revit models. And, finally, if you need to export or import the dwg file format, you should now have a successful workflow.
For those of you who are “audible” learners I would be happy to produce a video tutorial and email it directly. Just let me know: phil.russo@obg.com
