Mysterious settings in BrepOffsetAPI_ThruSections

Mauro Mariotti
Sat, 11/10/2012 - 01:00

Forums:

In BrepOffsetAPI_ThruSections, there are some mysterious methods to change its behaviour.
Does anyone know their meaning and use?

void SetSmoothing (const Standard_Boolean UseSmoothing)
"Define the approximation algorithm"

The following method has effect just if UseSmoothing is true:

void SetParType (const Approx_ParametrizationType ParType)
"Define the type of parametrization used in the approximation",

where an Approx_ParametrizationType can have one of these values:
Approx_ChordLength
Approx_Centripetal
Approx_IsoParametric

The following method has effect just if UseSmoothing is false:

void SetCriteriumWeight(const Standard_Real W1, const Standard_Real W2, const Standard_Real W3)
"define the Weights associed to the criterium used in the optimization"

void CheckCompatibility (const Standard_Boolean check=Standard_True)
I guess that the aim of this is to orient the wires in a consistent way.

The default values are:

smoothing: false;
criterium weights: 0.4, 0.2, 0.4;
parametrization type: ChordLength
check compatibility: true

Thanks again.
Mauro

Timo Roth
Wed, 05/14/2014 - 16:59

Dear Mauro,

what you wrote regarding which method has effect if UseSmoothing is true/false is not correct.

See the following code from BRepOffsetAPI_ThruSections::TotalSurf

if(myUseSmoothing) {
anApprox.SetCriteriumWeight(myCritWeights[0], myCritWeights[1], myCritWeights[2]);
anApprox.PerformSmoothing(line, section);
}
else {
anApprox.SetParType(myParamType);
anApprox.Perform(line, section, SpApprox);
}

So, only if UseSmoothing is true, SetCriteriumWeight has effect.
Only if UseSmoothing is false, SetParType has effect.

I also think that the documentation should be improved here regarding the Smoothing.

In OCC 6.3.1 Release Notes I found the following:

Advanced approximation method (implemented in class AppDef_TheVariational) has been
included in algorithms for creation of curves and surfaces:
􀂃 GeomAPI_PointsToBSpline,
􀂃 GeomAPI_PointsToBSplineSurface,
􀂃 Geom2dAPI_PointsToBSpline,
􀂃 GeomFill_AppSurf,
􀂃 BRepOffsetAPI_ThruSection

Here is an explanation about the meaning of the weight parameters for smoothing:
http://www.opencascade.org/org/forum/thread_345/?forum=3

When I tried smoothing with more complex surfaces, I often got exceptions. Does anyone have experience with smoothing / using AppDef_TheVariational? What are the requirements in order to use it successfully?

Kind regards,
Timo