Uncategorized error due to IFCCartesianPointList3D

[Surya7032]

Hi Team,

I am working on a project to generate IFC4 files using Xbim Essentials (version: V5.1.259). While creating IfcCartesianPointList3D, I observed a validation error when validating the generated IFC file against the IFC4 schema.

For example, the generated entity looks like:
#123 = IFCCARTESIANPOINTLIST3D((...),$);

However, as per the IFC4 schema definition (https://validate.buildingsmart.org/report_schema/r771713286), the $ (TagList) argument is not expected in this context, leading to a validation error. We had previously raised this issue (#639) and the suggestion was to move to IFC4x3. While IFC4x3 resolves this issue, we still need to support IFC4 due to a large existing customer base, and transitioning all consumers to IFC4x3 will take time.

On further analysis, I went through the Xbim Essentials source code and found that the implementation of IfcCartesianPointList3D differs between IFC4 and IFC4x3 (https://github.com/xBimTeam/XbimEssentials/blob/master/Xbim.Ifc4/GeometricModelResource/IfcCartesianPointList3D.cs). Based on this, I implemented a fix by removing the optional TagList parameter in the IFC4 implementation, which resolves the validation issue. The proposed change is available here: https://github.com/xBimTeam/XbimEssentials/pull/659/changes.

Could you please review this approach and confirm if it aligns with the expected handling of IFC4 validation? Additionally, I would like your guidance on whether this change is suitable to be formally incorporated into the Xbim Essentials codebase.

Thanks and Regards,
Surya

[andyward]

Hi @Surya7032 yes I remember. The options got discussed in #473 (comment)

I think it's pragmatic to remove the TagList attribute from IFC4 and lose support for it in the (deprecated) IFC4.1/4.2 schemas. However we need to be aware xbim's IFC schema is code-generated so your manual edits might be reversed in future if we re-generate the schema classes.

As such I'd like to investigate the second option I proposed where we have conditional serialisation. Let me look at that...

What may be useful in the interim is a unit test on your PR to pick up any future regression of the code if we do regenerate.

[Surya7032]

Hi @andyward ,
I hope this aligns with the solution you were referring to—introducing support for IFC4.1/4.2 export serialization by leveraging the internal distinction between XbimSchemaVersion.Ifc4x1 and XbimSchemaVersion.Ifc4, such that attributes like TagList are not serialized when targeting IFC4.

If this approach is planned to be implemented, we would be happy to adopt it. Could you please share a tentative timeline for when this fix is expected to be merged into the codebase?