xBimTeam
IFC4 cartesian point list invalid syntax
Creating an IfcStore model from an IFC 4 file held the wrong syntax for the IfcCartesianPointList2D and IfcCartesianPointList3D objects.
Specifically, it adds a trailing attribute after the coordinate list.
Assemblies and versions affected:
Xbim.Ifc4 6.0.445
Steps (or code) to reproduce the issue:
Opening a file with valid syntax for IfcCartesianPointList2D entities and inspecting the model already shows the trailing attribute (no need for additional operations)
// Step 1: load the model
var model = IfcStore.Open("file.ifc");
// Step 2: save to a different file
model.SaveAs("path");
Minimal file to reproduce the issue:
Expected behavior:
Saved IFC 4 file after Xbim manipulation held valid ifc coordinates list entities
Actual behavior or exception details:
The saved file fails the validation
Additional Details
Looking into the documentation for various IFC standard versions, we figured that the definition of IfcCartesianPointList2D and IfcCartesianPointList3D changed moving from IFC 4 to IFC 4x3: in the former version, they both have a single attribute CoordList; the latter version introduced a second attribute TagList.
During the validation of the exported IFC file, we got the following error:
Wrong number of attributes on instance with id #304 expected 1 got 2:
#304=IFCCARTESIANPOINTLIST2D(((-0.080000000000029464,-9.3800000000000026),(0.079999999999968818,-9.3800000000000026),(0.080000000000025134,9.379999999999999),(-0.079999999999973148,9.379999999999999),(-0.080000000000029464,-9.3800000000000026)),$);
where you can see that the offended line has an unexpected second attribute (namely $).
Inspecting the IfcCartesianClassPointList2D.cs and IfcCartesianClassPointList3D.cs files in XbimEssential/Xbim.Ifc4/GeometricModelResource it seems that the TagList attribute is wrongly defined in the interface also for version IFC 4:
public partial interface @IIfcCartesianPointList2D : IIfcCartesianPointList
{
IItemSet<IItemSet<IfcLengthMeasure>> @CoordList { get; }
IItemSet<IfcLabel> @TagList { get; }
}
A quick bit of investigation. IIfcCartesianPointList3D.TagList was not in IFC4.0 ADD2_TC1 but was added in IFC4.1 RC3, which was integrated in xbim April 2018. It was also in IFC4.2 and remains in IFC4.3_ADD2
However IFC4x1 (and 4x2) were subsequently withdrawn by BuildingSmart with the 4.3 release
Unfortunately IFC4 as a family of schemas doesn't really differentiate the exact schema used in the header. It's just FILE_SCHEMA(('IFC4')); regardless of whether it's IFC4 ADD2 TC1 (official) or a later IFC4x1/x2, so we can't rely on that to indicate schema support.
I guess the options are:
- Revert xbim.IFC4 back to IFC4_ADD2_TC1 and lose support for any remaining 4.1/4.2 changes
- Introduce some support for IFC4.1/2 export serialisation - given we have an internal concept of
XbimSchemaVersion.Ifc4x1vsXbimSchemaVersion.Ifc4- i.e. don't serialise Taglist etc if IFC4 - Leave alone with this edge-case and acknowledge some extraneous params may be included in exports. (Along with validation errors) - not a great option!
What do you think @martin1cerny?
