nurbs and free form bodies as IfcAdvancedBrep

bernd

Ifc4 does support free form bodies by the use of IfcAdvancedBrep. IfcOpenShell and thus FreeCAD does support this as well. This opens endless possibilities. I have been trying them from time to time. Just gave it another try today. Here some informations ...

https://standards.buildingsmart.org/IFC/DEV/IFC4_2/FINAL/HTML/schema/ifcgeometricmodelresource/lexical/ifcadvancedbrep.htm

To export them out of FreeCAD make sure:

• preferences Arch IFC-Version ... "IFC4"
• preferences IFC export ... activate "Use IfcOpenShell serializer if available"
• topic on FreeCAD forum ... https://forum.freecad.org/viewtopic.php?t=40378

https://github.com/IfcOpenShell/IfcOpenShell/issues/586

Lots of viewers do have heavy problems parsing these IfcAdvancedBrep. I do not know about CAD, like Revit, ArchiCAD and VectorWorks. Allplan does well.

How about BlenderBIM? Is Blender able to create free form bodies? As it is a mesh software it might not suited for this? But since I am a FreeCAD guy I do not know about this.

cheers bernd

bernd

some Shapes exported with Allplan and imported in view.ifcopenshell.org

Moult

At the moment we treat AdvancedBReps as meshes in Blender. In the future we'll probably build some native editing tools for them, but at the moment it's not a high priority, not to mention it's not an easy task.

Revit has recently been abusing advanced BReps unfortunately. Even for things that could be simple extrusions (simple boxes, for instance) they revert to using advanced BReps which is pretty terrible. Not only is it geometrically inappropriate, due to the poor support in viewers many people say "Oh IFC doesn't work". Shame on you, Revit.

bernd

@Moult said:
At the moment we treat AdvancedBReps as meshes in Blender. In the future we'll probably build some native editing tools for them, but at the moment it's not a high priority, not to mention it's not an easy task.

Good to know. YEAH a tool to edit Nurbs is for sure not an easy task but would be awesome to have in BB.

@Moult said:
Revit has recently been abusing advanced BReps unfortunately. Even for things that could be simple extrusions (simple boxes, for instance) they revert to using advanced BReps which is pretty terrible. Not only is it geometrically inappropriate, due to the poor support in viewers many people say "Oh IFC doesn't work". Shame on you, Revit.

YEAH lots of software out there have very poor support for IfcAdvancedBrep ... Especially Solibri has very poor support. May be one reason they decided not to export them any longer. But some software have really improved since the first time I tried them back in May 2019. I may post some pics in the topic here ...

In our company we have started to do BIM workflows for streets bridges and similar objects. For them real geometry is really needed in some cases. The use of polylines or meshes is not really an good option for them. A spiral curve or a clothoid is just not a polyline.