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IDProjectCategoryView StatusLast Update
0032968CommunityOCCT:Data Exchangepublic2022-05-14 21:47
Reportermr baley Assigned Tobugmaster  
PrioritynormalSeverityjust a question 
Status closedResolutionno change required 
PlatformWindowsOSVC++ 2022 
Product Version7.6.0 
Target Version7.7.0 
Summary0032968: TopLoc_Location::IsEqual and BRep_CurveOnSurface::IsCurveOnSurface seem to not match with each other
DescriptionI'm trying to use BRep_Tool::CurveOnSurface to retrieve a Handle(Geom2d_Curve).

I'm working with a step model i imported using STEPControl_Reader.

The model is correctly displayed.

I also checked the TopoDS_Edge and the TopoDS_Face i'm passing to BRep_Tool::CurveOnSurface with BRepCheck_Analyzer and it returns IsValid() == true for both.

When debugging i can see that the BRep_TEdge contains four BRep_CurveRepresentation, a BRep_Curve3D, two BRep_CurveOnSurface and a BRep_CurveOn2Surfaces.

BRep_Tool::CurveOnSurface iterates through all BRep_CurveRepresentation of the TopoDS_Edge and calls BRep_CurveOnSurface::IsCurveOnSurface for each BRep_CurveRepresentation.

BRep_CurveOnSurface::IsCurveOnSurface compares the surfaces by pointers and the TopLoc_Locations using this Equal implementation which, and this is the reason why in this case BRep_Tool::CurveOnSurface returns a null Handle, returns false if one returns true for IsIdentity().

I honestly don't know what's the reasoning behind this implementation.

I was thinking that maybe transformations are not supposed to be empty (because that's what TopLoc_Location::IsIdentity() checks) but STEPControl_Reader doesn't report any errors and BRepCheck_Analyzer says everything is valid.

I might be able to work around this by looping through all curves myself and replacing empty location with actual identity transformations but it feels wrong.

What am i missing?
Steps To ReproduceIterate through all edges, take the first face of each, and try BRep_Tool::CurveOnSurface
Additional information
and documentation updates
I'm unsure what's the better place; i also posted this here:
TagsNo tags attached.
Test case number

Issue History

Date Modified Username Field Change
2022-05-11 20:48 mr baley New Issue
2022-05-11 20:48 mr baley Assigned To => msv
2022-05-11 20:48 mr baley File Added: problem.stp_.7z
2022-05-11 21:00 mr baley File Deleted: problem.stp_.7z
2022-05-11 21:01 kgv Category OCCT:Modeling Data => OCCT:Data Exchange
2022-05-11 21:01 kgv Product Version 7.7.0 => 7.6.0
2022-05-12 14:00 mr baley Assigned To msv => gka
2022-05-12 14:00 mr baley Status new => resolved
2022-05-12 14:00 mr baley Note Added: 0108411
2022-05-12 15:59 kgv Assigned To gka => bugmaster
2022-05-12 15:59 kgv Status resolved => feedback
2022-05-14 21:47 azv Status feedback => closed
2022-05-14 21:47 azv Resolution open => no change required