BlenderBIM imported geometry wrong

B by bernd on 27 Aug 2020, edited 1 Sep 2020 #

IFC exported with FreeCAD. Test in lots of viewer, all do well except BlenerBIM. See https://forum.freecadweb.org/viewtopic.php?f=39&t=49689#p426689

M by Moult on 27 Aug 2020 #

@bernd the BlenderBIM Add-on is correct, I believe. The IFC file has duplicate GlobalIds - clearly other IFC viewers (including the web based IfcConvert) are lenient. Perhaps a bug in FreeCAD?

This will fix it:


>>> f = ifcopenshell.open('/home/dion/drive/bim/DhFundament.ifc')

>>> for e in f.by_type('IfcElement'):

...     e.GlobalId = ifcopenshell.guid.new()

>>> f.write('/home/dion/drive/bim/DhFundament2.ifc')

C by CadGiru on 27 Aug 2020 #

@moult, @bernd

Thx for investigations.

D by duncan on 27 Aug 2020 #

I think it would be great if BlenderBIM Add-on also can be lenient, and offer a report of errors and warnings.

M by Moult on 27 Aug 2020 # +2 votes

@duncan for some things, the BlenderBIM Add-on is lenient - the validate tool will also produce a report of errors and warnings. This is not one of those cases, unfortunately. When building an authoring tool - the GlobalId is an indicator of whether or not an element already exists - needed for the ability to "refresh / reload" an existing model. This is not required in a pure viewer, which can just re-display with minimal computing expense. This is why it is strict here.

B by bernd on 28 Aug 2020, edited 28 Aug 2020 #

Thanks for the very fast debuging.

Yeah bug in FreeCAD. On first export of an object to ifc it gets a ifcuid. If the object is somehow copied inside FreeCAD the id will not changed. Thus identical ids on next export. See https://forum.freecadweb.org/viewtopic.php?f=39&t=49689&p=426885#p426885

cheers bernd

B by bernd on 28 Aug 2020 # +2 votes

BTW: it is good to have some software which is very strict with ifc standard. We would not have found this bug. Well done BlenderBIM :-)

B by bernd on 31 Aug 2020, edited 31 Aug 2020 # +1 votes

@Moult

How do you solve this in Blender? A object should keep his uuid over his livetime, no matter how often a project is saved to Blender format, even under a different file name. But if a object is copied, no matter which tools of Blender is used to copy the uuid should be reseted and a new should be used.

That is exactly the problem in FreeCAD. ATM the id is saved just in a dict. If an object is copied the id is duplicated. It is impossible to attrac this in the copy method as there are dozens of possibilities to copy a object in FreeCAD. I opened a topic about this but it is not solved yet: https://forum.freecadweb.org/viewtopic.php?f=10&t=49818

M by Moult on 31 Aug 2020 #

@bernd in Blender, there are two ways to solve it. The first is to have a callback watching the depgraph - whenever an object is copied, it can automatically reset just that attribute. The second way is to leave the attribute as a duplicate, and wait for the user to manually resolve it, or resolve it at export time and force a new GlobalId at export time when it detects a duplicate GlobalId.

I use the second approach.

B by bernd on 1 Sep 2020, edited 1 Sep 2020 #

@Moult said:

leave the attribute as a duplicate, and wait for the user to manually resolve it, or resolve it at export time and force a new GlobalId at export time when it detects a duplicate GlobalId.

If you find a duplicate GlobalId on export? How do you know which one is the original and which is the copy?

M by Moult on 1 Sep 2020 #

@bernd the copy is later in the list of objects.

B by bernd on 1 Sep 2020 #

:-)

exactly this was my first idea for FreeCAD too ... But I am not 100 % happy with it because it might be not failsafe in all cases.

I might go for this for a first fast solution.