[IFC] Is there any other software product that uses IfcProjectedCRS and IfcMapConversion ?

Martin156131

Here is an example ifc file with IfcProjectedCRS and IfcMapConversion: https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/annex_e/placements-and-gis-referencing/geographic-referencing-utm.html

I did open it in Solibri Anywhere, BimCollab ZOOM, BimVision, ACC and BlenderBIM. Only in BlenderBIM i saw the IfcProjectedCRS and IfcMapConversion. In the other viewer i did not see any difference if i comment out the IfcProjectedCRS and IfcMapConversion line.

Is there any other software product that uses IfcProjectedCRS and IfcMapConversion ?

I only know that it is possible to export ifc file from Revit or Civil3D with IfcProjectedCRS and IfcMapConversion. Not sure what happens in a import.

Moult

A lot of software supports writing the CRS / MapConversion. Like Revit, Civil3D, 12D, Tekla, ArchiCAD. Very few software actually do anything with it or use it in their spot coordinate calculations.

Note that you shouldn't "see" a difference, it's simply used in calculations should you wish to get a map coordinate from a local coordinate.

Martin156131

I did a little test. In BIMcollab ZOOM, it is possible to load two or more ifc files.

I loaded the ifc file from bSI: https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/annex_e/placements-and-gis-referencing/geographic-referencing-utm.html

And then i made a copy of the ifc file and changed the z value in the IfcMapConversion

My expectation was, that the geometry would load 1 m shifted, however BIMcollab ZOOM did not take the IfcMapConversion in account.

Moult

Correct. And this is because tools like BIMCollab ZOOM only federates models using local model coordinates, not map coordinates. A conversion to map coordinates is potentially a complex process, involving a scale in the XY plane (so a sphere would become an ellipsoid - and would also mean that everything needs to be faceted for the calculation to be straightforward). As such, they simply avoid the process altogether and probably let the user specify a manual transformation elsewhere (but will not accommodate XY scaling).

In theory it can detect when a scale factor is not present and do that "rigid" transformation which is a lot cheaper.

BBIM does the same thing. It will only deal with local coordinates. Sooner or later though we should build a utility for it, and definitely at least handle rigid transformations out of the box (in IFC4.3 rigid transformations become explicit which will help).

Edit: are you sure you changed the Z value or the X Axis Abscissa in your screenshot?

Martin156131

@Moult you are correct i did now a new test

However the result was the same in BIMcollab ZOOM

Martin156131

In ACC they do not ignore IfcMapConversion, see image

Moult

@Martin156131 nice! That's news to me, and kudos to Autodesk for getting that right!