BSpline to and from IGES (... or other)

Luc Wens's picture
Luc Wens
Sat, 01/21/2023 - 16:15
Forums: 
Data Exchange and Application Framework

I want to write/read a BSPline to/from file.

Writing to IGES is quite trivial:

	Handle(Geom_BSplineCurve)	m_hBSpline;
	IGESControl_Writer IgesWriter;
	IgesWriter.AddGeom(m_hBSpline);
	IgesWriter.Write("somefile.igs");

And this write the spline as entity 126 to the IGES file

If I look at IGESCAFControl_Reader for reading the spline, typically a TopoDS_Shape is returned, so in the case of a spline you would get a wire.
But I would like to get the original spline back: poles, breaks,....

I did find some traces back
IGESConvGeom::SplineCurveFromIGES can be used to convert IGESData_IGESEntity to Geom_BSplineCurve, so that is getting close to what I want.

How can I get all the IGESData_IGESEntity out of my iges file?
IGESControl_Reader::IGESModel returns only 1 Entity.

Luc Wens's picture
Luc Wens
Sat, 01/21/2023 - 18:36

Did a bit of further research and came up with this 

	IGESControl_Reader aReader;
	IFSelect_ReturnStatus stat = aReader.ReadFile(FilePath);
	if (stat != IFSelect_RetDone)
		return false;

	Handle(IGESData_IGESModel) IgesDataModel = aReader.IGESModel();

	IGESToBRep_BasicCurve Convertor;
	for (int i=1;i<=IgesDataModel->NbEntities();i++)
	{
		Handle(IGESData_IGESEntity)		IgesEntity = IgesDataModel->Entity(i);
		Handle(IGESGeom_BSplineCurve)	hIGESSpline = Handle(IGESGeom_BSplineCurve)::DownCast(IgesEntity);
		if (hIGESSpline)
		{
			Handle(Geom_Curve) hGeomCurve = Convertor.TransferBSplineCurve(hIGESSpline);
			if (hGeomCurve)
			{
				m_hBSpline = Handle(Geom_BSplineCurve)::DownCast(hGeomCurve);
				if (m_hBSpline)
					return true;
			}
		}
	}