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#CV-2x3-170

requirement to provide a fall-back configuration to export b-rep instead of CSG shape representations
number
CV-2x3-170
based on
IFC2x3
effects
IFC2x3 coordination view 2.0
date
24. Oct 2011
initiator
ISG meeting in Budapest
summary requirement to provide a fall-back configuration to export b-rep instead of CSG shape representations

 

Description

With the IFC2x3 Coordination View V2.0 the ability to use Constructive Solid Geometry (CSG) has been added to the supported geometric representations. This may impose a backward compatibility issue with software applications, that still (only) support the IFC2x3 Coordination View V1.0. Therefore the following agreement is imposed:

  • The software application supporting export of CSG shape representations*) shall have an export configuration setting to enable the export of "CSG" geometry as an option for the IFC2x3 Coordination View V2.0.
  • However the default export setting for the IFC2x3 Coordination View V2.0 shall disable "CSG" to avoid incompatibility issues with current IFC import interfaces. The default setting shall force the export as "Brep" shape representation for those elements.
  • The export setting shall only affect the elements otherwise being exported as CSG, and not all element shape representations (i.e. it is not a replacement of the IFC2x3 simple presentation view having ALL elements exported as Brep's), also as "CSG" is a solid, the "Brep" representation is required (being a solid) and not a surface model representation.
  • The export setting user interface shall have a proper explanation that the "CSG" setting may cause interoperability issues with older IFC implementations (e.g. the previous "IFC2x3 Coordination View V1.0")

 

NOTE  Within the IFC2x3 Coordination View V2.0 certification process a second test file (not containing "CSG" representation) is required for each export test case having a test file with CSG shape representations.

*) an CSG shape representation is declared as:
- IfcShapeRepresentation.RepresentationIdentifier = "Body"
- IfcShapeRepresentation.RepresentationType = "CSG"

#1000= IFCSHAPEREPRESENTATION(#100,'Body','CSG',(#1010));