Link placements

[yorikvanhavre]

Link FreeCAD placements to underlying IFC placements. We need the following functionality:

• When the placement of a FreeCAD object changes, change the underlying IFC placement
• IFC supports local placements. A local placement is a placement that refers to another placement as its "father". There is a decision to be taken here, how do we reflect this in FreeCAD
• A change to any placement in the IFC file that affects a local placement should be reflected in the FreeCAD objects as well. Need to investigate if, for ex, a storey being moved 2 meters up affects the objects inside as well

IfcOpenShell related structures: https://blenderbim.org/docs-python/autoapi/ifcopenshell/util/placement/index.html https://blenderbim.org/docs-python/autoapi/ifcopenshell/api/geometry/edit_object_placement/index.html

[yorikvanhavre]

Interesting discussion linked to this: https://github.com/yorikvanhavre/FreeCAD-NativeIFC/issues/14 Basically we can consider the global/local placement issue as handled internally by IfcOpenShell and just concentrate on what we are showing the user, that is, the final position of the object.

[yorikvanhavre]

This contains good examples: https://github.com/IfcOpenShell/IfcOpenShell/blob/v0.7.0/src/ifcopenshell-python/test/api/geometry/test_edit_object_placement.py