Understanding Revit Coordinate
In this post, I am going to explain one of the most complicated topics in Revit. I don’t think that there is a 100% future-proof workflow that everyone would follow, but there is a well-known workflow that most people prefer to do so. Before getting too further, it is important to understand what they are.
What is it?
Revit coordinate system has three reference points that act differently namely: Internal origin, project base point and survey point.
Why is it so important?
When starting a project, we need to locate the model in the virtual location. The location should be matched to the real site which is measured by a surveyor. The survey plan is normally provided as a 2d cad file, so the information should be transferred correctly. When doing this, the coordinate is used. Some used Project Base Point to match the coordinate, whereas others use Survey Point. It should be clearly stated in the BEP or BMP how to set up the coordinate so that confusion can be prevented.
When linking a dwg file into Revit, it is crucial that it should be located within 16km (32km diameter) of its internal origin. Otherwise, graphics will not be shown properly. However, in general, the survey is situated at a far distance from 0,0,0 since it is used the actual distance. Therefore, it should be carefully considered to use the positioning as ‘centre to centre’ and manually re-locate the plan. In general, they are turned off in most views, so make sure they are turned on in the visibility/graphic. You can find them under the Site category.
Different Coordinate Systems in Revit
Most people didn’t know its existence as it was not visible before. However, Autodesk provided the sub-category to show the internal origin from Revit 2020 as some people want to see it. This origin point in Revit means 0,0,0 in AutoCAD and it cannot be moved and selected.
Project Base Point
Project Base Point is a customisable origin that can be defined as a start point although it is not an actual 0,0,0. Once set up the project base point, then all the views with project north will be adjusted accordingly.
As Revit only allows 32km workspace, Project Base Point should be within it. Otherwise, it will cause some issues in the future.
It is recommended to match the location to Internal Origin, but not compulsory.
Survey point is used to indicate the real-world coordinate that is given by a surveyor. Some prefer to make it 0,0,0, whereas others would match the coordinate values written in the survey. It is the BIM manager’s choice whether it is 0,0,0 or to match the coordinate from the survey although it doesn’t really affect the project. Ask your surveyor to get the site coordinate, do not rely on the CAD file. It must be written in the drawing.
What do we really need to know?
Revit unnecessarily has this coordinate system and it is quite difficult to understand why they are actually existing. However, we can make it simple. Let's remember this workflow when setting up the file. Just use Project Base Point to indicate the coordinate. Specify the Survey Point to indicate the coordinate, and then use Project Base Point for project reference (starting) point like 0,0,0 in AutoCAD.
It is highly recommended to turn off those points unless you actually need to work on them since there are potential risks that someone accidentally modifies the coordinate which will lead to hell.