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IDProjectCategoryView StatusDate SubmittedLast Update
0029745Community[OCCT] OCCT:Modeling Datapublic2018-05-08 17:552020-12-22 11:55
Reporterventu 
Assigned Toakaftasev 
PrioritynormalSeveritycrash 
StatusfeedbackResolutionopen 
PlatformOSOS Version
Product Version[OCCT] 7.2.0 
Target VersionFixed in Version 
Summary0029745: GeomAdaptor_Surface::VIntervals fails on periodic surfaces
DescriptionSuppose:
_ we have a V periodic NURBS Surface;
_ we have a GeomAdaptor_Surface with V limits outside of the period;
_ the surface has discontinuities;
_ we call GeomAdaptor_Surface::VIntervals to get a list of continuous subintervals.

That method will build an U iso-curve and get such intervals on that; at the end, however, that intervals are bounded with:
  T(T.Lower()) = myVFirst;
  T(T.Lower() + myNbVIntervals) = myVLast;

The problem arises since the value returned by the curve Intervals(...) method will be within the period, so those values will be invalid.


Example:
_ surface with periodic V knot vector ranging [0 ; 4];
_ surface adaptor with limits [5 ; 6].
_ Intervals(...) on the ISO curve returns [1,2,3];
_ the statements reported above will transform the result in [5,2,6].

This will lead to a crash in subsequent processing.



A solution along the line of the following might work:
  if (mySurface->IsVPeriodic())
    for (Standard_Integer i=T.Lower()+1;i<T.Lower()+myNbVIntervals;++i)
      T(i)+=myVFirst-T(T.Lower());
  T(T.Lower()) = myVFirst;
  T(T.Lower() + myNbVIntervals) = myVLast;


Notice the problem should also occur in U direction.
TagsNo tags attached.
Test case number
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-  Notes
(0096583)
akaftasev (developer)
2020-11-06 11:58

 Dear ventu, can you attach more detailed steps to reproduce current bug, because according to this description it is hard to reproduce it
(0097726)
ventu (reporter)
2020-12-18 18:35

 TL;DR
Changes made in 7.4.0 prevent this bug from happening again.
However, I'm not sure the new result is correct either.



The problem arose while importint a STeP model and I'm having an hard time reproducing it programmatically (even with 7.3.0).

In any case, please take a look at the following code:
  TColgp_Array2OfPnt Poles(1,2,1,3);
  Poles(1,1)=gp_Pnt(0,0,0); Poles(2,1)=gp_Pnt(0,0,1);
  Poles(1,2)=gp_Pnt(1,0,0); Poles(2,2)=gp_Pnt(1,0,1);
  Poles(1,3)=gp_Pnt(1,1,0); Poles(2,3)=gp_Pnt(1,1,1);
  //Poles(1,4)=gp_Pnt(0,0,0); Poles(2,4)=gp_Pnt(0,0,1);
  TColStd_Array1OfReal UKnots(1,2),VKnots(1,4),ResultsA(1,4),ResultsB(1,4);
  UKnots(1)=0; UKnots(2)=1;
  VKnots(1)=0; VKnots(2)=1; VKnots(3)=2; VKnots(4)=3;
  TColStd_Array1OfInteger UMult(1,2),VMult(1,4);
  UMult(1)=2; UMult(2)=2;
  VMult(1)=1; VMult(2)=1; VMult(3)=1; VMult(4)=1;
  Handle(Geom_BSplineSurface) S=new Geom_BSplineSurface(Poles,UKnots,VKnots,UMult,VMult,1,1,false,true);
  GeomAdaptor_Surface A(S,0,1,0,3);
  A.VIntervals(ResultsA,GeomAbs_C1);
  for (TColStd_Array1OfReal::const_iterator i(ResultsA.begin());i!=ResultsA.end();++i) std::cout<<*i<<" ";
  std::cout<<std::endl;
  GeomAdaptor_Surface B(S,0,1,3,6);
  B.VIntervals(ResultsB,GeomAbs_C1);
  for (TColStd_Array1OfReal::const_iterator i(ResultsB.begin());i!=ResultsB.end();++i) std::cout<<*i<<" ";
  std::cout<<std::endl;

Output I'd expect (but possibly I'm wrong):
0 1 2 3
3 4 5 6

Output I get (with OC 7.3.0):
0 1 2 3
3 6 0 0

Notice here two values are missing.
This is not the original problem I reported and which I'm unable to reproduce now: in that case what I was getting in the second line was the equivalent of 3 1 2 6.



7.4.0 changed this behaviour: at line 441 of GeomAdaptor_Surface.cxx, "break" was replaces with a "return".
So the code at the end of the function, that changes only the first and last value, is not executed, and what I originally reported cannot happen anymore.

Still I'm wondering whether "3 6" is to be expected or if we just exchanged a bug for another.

- Issue History
Date Modified Username Field Change
2018-05-08 17:55 ventu New Issue
2018-05-08 17:55 ventu Assigned To => msv
2020-11-02 10:41 szy Assigned To msv => akaftasev
2020-11-02 10:41 szy Status new => assigned
2020-11-06 11:58 akaftasev Note Added: 0096583
2020-11-06 11:58 akaftasev Assigned To akaftasev => ventu
2020-11-06 11:58 akaftasev Status assigned => feedback
2020-12-18 18:35 ventu Note Added: 0097726
2020-12-22 11:55 ventu Assigned To ventu =>
2020-12-22 11:55 ventu Assigned To => akaftasev

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