How to get IfcRelNests?

[Rick]

The attached file uses IfcRelNests to relate IfcAlignmentHorizontal and IfcAlignmentVertical to IfcAlignment (this format began with 4x3 rc2). When extracting data from the model, IfcAlignment->Nests() returns an empty container. Here is sample code and the file I'm trying to read.

Thanks

int main(int argc,char** argv)
{
   // Redirect the output (both progress and log) to stdout
   Logger::SetOutput(&std::cout, &std::cout);

   // Parse the IFC file provided in argv[1]
   IfcParse::IfcFile file(argv[1]);
   if (!file.good()) {
      std::cout << "Unable to parse .ifc file" << std::endl;
      return 1;
   }

   auto alignments = file.instances_by_type<Ifc4x3_rc2::IfcAlignment>();
   auto alignment = *(alignments->begin());
   auto nests = alignment->Nests();
   for (auto rel_nests : *nests) // nests->size() == 0 so the loop is skipped over
   {
      auto related_objects = rel_nests->RelatedObjects();
      for (auto related_object : *related_objects)
      {
         auto horizontal_alignment = related_object->as<Ifc4x3_rc2::IfcAlignmentHorizontal>();
         auto vertical_alignment = related_object->as<Ifc4x3_rc2::IfcAlignmentVertical>();
         if (horizontal_alignment)
         {
            // do something
         }
         else if (vertical_alignment)
         {
            // do something
         }
      }
   }
    return 0;
}

[Thomas Krijnen]

Sorry for the late reply. I find it confusing as well, but you're traversing the inverse relationship in the wrong direction. The correct attribute here is IsNestedBy.

Nests you can call on the hor/ver alignment.

A quick headsup that the file is not very valid.

The parser gives these errors

[Error] Wrong number of attributes on instance with id #28
[Error] Wrong number of attributes on instance with id #29

The schema validator gives these errors

Validating Alignment-Aplitop-2.IFC
In #97=IfcCurveSegment(.CONTINUOUS.,#93,IfcNonNegativeLengthMeasure(0.),IfcNonNegativeLengthMeasure(497.87228283))
IfcNonNegativeLengthMeasure(497.87228283) not valid for <attribute ParentCurve: <entity IfcCurve>>
In #88=IfcCurveSegment(.CONTINUOUS.,#84,IfcParameterValue(-2164.89830648556),IfcNonNegativeLengthMeasure(646.6491343))
IfcNonNegativeLengthMeasure(646.6491343) not valid for <attribute ParentCurve: <entity IfcCurve>>
In #79=IfcCurveSegment(.CONTINUOUS.,#75,IfcNonNegativeLengthMeasure(0.),IfcNonNegativeLengthMeasure(393.90380198))
IfcNonNegativeLengthMeasure(393.90380198) not valid for <attribute ParentCurve: <entity IfcCurve>>
In #70=IfcCurveSegment(.CONTINUOUS.,#66,IfcNonNegativeLengthMeasure(0.),IfcNonNegativeLengthMeasure(928.81668938))
IfcNonNegativeLengthMeasure(928.81668938) not valid for <attribute ParentCurve: <entity IfcCurve>>
In #61=IfcCurveSegment(.CONTINUOUS.,#57,IfcParameterValue(-1099.36986773),IfcNonNegativeLengthMeasure(1099.36986773))
IfcNonNegativeLengthMeasure(1099.36986773) not valid for <attribute ParentCurve: <entity IfcCurve>>
In #52=IfcCurveSegment(.CONTINUOUS.,#47,IfcNonNegativeLengthMeasure(0.),IfcNonNegativeLengthMeasure(834.76720476))
IfcNonNegativeLengthMeasure(834.76720476) not valid for <attribute ParentCurve: <entity IfcCurve>>
In #42=IfcCurveSegment(.CONTINUOUS.,#35,IfcNonNegativeLengthMeasure(0.),IfcNonNegativeLengthMeasure(688.33801902))
IfcNonNegativeLengthMeasure(688.33801902) not valid for <attribute ParentCurve: <entity IfcCurve>>
Attribute <entity IfcAlignmentHorizontal>.<attribute Segments: <list [1:?] of <entity IfcAlignmentHorizontalSegment>>> not optional
Attribute <entity IfcAlignment>.<attribute Axis: <entity IfcCurve>> not optional
In #115=IfcCurveSegment(.CONTINUOUS.,#111,IfcNonNegativeLengthMeasure(0.),IfcNonNegativeLengthMeasure(100.))
IfcNonNegativeLengthMeasure(100.) not valid for <attribute ParentCurve: <entity IfcCurve>>
In #106=IfcCurveSegment(.CONTINUOUS.,#102,IfcParameterValue(-461.366),IfcNonNegativeLengthMeasure(461.366))
IfcNonNegativeLengthMeasure(461.366) not valid for <attribute ParentCurve: <entity IfcCurve>>

[Rick]

Thanks for the clarification. It seems alignment->Nests() would be right because I want to know what is nested inside the alignment. Since alignment->IsNestedBy() is correct, then I'll update my brain.

Very interesting about the file. I pulled it from bSI-InfraRoom/IFC-infra-unit-test on github.

How do you dump the schema validation errors?

[Thomas Krijnen]

I find the "active" form using verbs also confusing. I would have picked something like IsPartOf and HasParts and then some property on the relationship whether it is containment/decomposition/nesting.

The schema validation errors you can find with ifcopenshell-python. If you have it installed it's simply:

 python -m ifcopenshell.validate my_file.ifc