Autodesk
Import an IFC using the angle to true north to influence rotation
When an IFC is imported, its local coordinates are always lined up to project north. This is a problem, because some IFC files (i.e. from ArchiCAD) are already rotated such that grid north is orthogonal, not project north.
In Revit, there seems to be no way to influence the rotation of the imported IFC.
This has been mentioned before from web searches but with no solution:
- https://forums.autodesk.com/t5/revit-structure-forum/export-link-ifc/td-p/5817251
- https://forums.autodesk.com/t5/revit-architecture-forum/linking-ifc-rvt-files-into-projects-with-project-north-differing/td-p/8206106
Thoughts?
@Moult when you say 'grid north' I assume that's the same as compass / map / true north right?
@DuncanLithgow actually, I do mean grid north. There are a few norths out there:
- Project north, an arbitrary orientation usually decided by the architect so that your building is drawn orthogonal
- Grid north, a direction towards north along the grid lines of a map projection. So when your surveyor gives you a survey with typically big numbers for eastings and northings, they use a map projection system (in Sydney we might use GDA94 / MGA 56, a.k.a. EPSG:28356). So when you georeference your model, "grid north" is up the page. This grid is typically orthogonal.
- True north, a.k.a geodetic north, the direction to the geographic north pole, the northenmost point of the earth. This direction is along the latitudes of the Earth. This is not the same as grid north. It typically deviates quite a bit. Since surveyors draw using grid north, this means that true north is actually a long a curve (i.e. along a latitude) and is not a constant. This true north is what we should use for solar / shadow analysis, and I've sometimes heard it called solar north.
- Magnetic north, which likes to shift around and is typically a bit useless for the AEC industry.
So, we draw in project north, survey / georeference in grid north, and solar analysis in true north.
Out of the three important ones, Revit supports only 2 depending on how you use Revit. This discrepancy leads to incorrect georeferencing or incorrect solar analysis typically. However, especially now that Revit is actually implementing IFC map conversion, getting grid north correct has the higher priority. Fixing Revit to work with the three norths is another issue. There should probably be another bug filed for how Revit stores true north in IFC/
Has this changed recently? When I link an IFC now the coordinates seems to align origin to origin but the rotation is alignet with the current "true north" angle
@eibre yes there was a change: https://github.com/Autodesk/revit-ifc/issues/522
There should be multiple options on the linking dialog, including the coordinate mapping. Now it is an inconsistent guessing game, which never behaves as expected.
