3D modeling & numerical simulation

Bug in Extrema_ExtPC

Bug in Extrema_ExtPC
 Steph 2012/12/19 20:02 Hi, I'm encountering some computing problems with the class Extrema_ExtPC. I use it to compute the projection of a point over a TopoDS_Wire. I need the point but also the parameter of the projected point on the wire. The way i use it is the next : ------------------------------------------------------------------------------- TopoDS_Wire originalWire --> "CURV2_P_Wire.brep" BRepAdaptor_CompCurve wireAdaptor(originalWire); Extrema_ExtPC extremaPoint(point,wireAdaptor,1E-1); if ( extremaPoint.IsDone() && extremaPoint.NbExt() > 0 ) { const Standard_Integer iNbExtremaPoints = extremaPoint.NbExt(); for (Standard_Integer i=1;i<=iNbExtremaPoints ;++i) { bool bIsMin = extremaPoint.IsMin(i); const Extrema_POnCurv& currentPOnCurv = extremaPoint.Point(i); const gp_Pnt& currentPoint = currentPOnCurv.Value(); const Standard_Real& currentParameter = currentPOnCurv.Parameter(); const Standard_Real& currentDistance = currentPoint.Distance(point); } } ------------------------------------------------------------------------------- In this case the algorithm find 3 solutions : Point 1 : IsMin=true; point=(1000.0,1000.0,0.0); param=0.0; distance=501.99 Point 2 : IsMin=false; point=(1986.98,1170.38,0.0); param=1.79; distance=1041.0 Point 3 : IsMin=false; point=(1000.0,1500.0,0.0); param=4.0; distance=1.99 The point 3 is the correct point and i expect this point to answer true to the IsMin method. But it is not the case. Moreover thanks to the distance it is easy to view that there is a problem. Thanks to say if you can reproduce this case. Moreover if someone can explain me what represent the tolerance parameter. With the default constructor value 1E-10 in this case found only one solution (point 2 !!) Thanks you. You have to be logged in to download the attached file
 Steph 2012/12/19 20:05 Sorry i forgot to put the point : const gp_Pnt point(999.99,1501.99,0.0); So i expect to get as nearest point the (1000.0,1500.0,0) point.
 Hennig 2012/12/19 20:26 hey steph, i cant tell you something about the parameter, but this would interest me too... somebody an idear? what i can tell you is that the function IsMin do not answer true, when your distance is the minimum... it answers True when your Extremafunction is a Minimum and not a Maximum. And of course there can be only one absolute minimum but more than one local minimum between your point and the curve. Thats why i check all distances to get the absolute minimum. greetings paul
 Steph 2012/12/21 15:17 Thanks Paul for the answer. I understand better. However if i have found a better way to compute the projection. In my case i'm not interested in getting all the extrema but only the projection to the nearest point over a wire. So i use ShapeAnalysis_Curve::Project. I've encountered some strange case of bad computing but increasing brutally the precision value (last parameter of the project method) it works in all the cases. So it work but i don't understand the precision parameter. Thanks.