Trimmed Nurbs Surface

Hi,

I am new to Opencascade and I hope that someone can help me with my problem:
What I want to do is to read an IGES-File and export the B-Spline surface information of the created shapes
(My aim is to use the spline surface information from Opencascade to create my own spline surfaces in an extern application.).
Ok, my code looks like this:

//Read IGES-File
Standard_Integer nIgesFaces,nTransFaces;
IGESControl_Reader myIgesReader;
IFSelect_ReturnStatus status = myIgesReader.ReadFile ("file.igs");
Handle(TColStd_HSequenceOfTransient) myList = myIgesReader.GiveList("iges-faces");
nIgesFaces = myList->Length();
nTransFaces = myIgesReader.TransferList(myList);

//Conversion of all found Shapes to Nurbs-Surfaces
for (int i=1; i {
TopoDS_Shape testShape = myIgesReader.Shape(i);
BRepBuilderAPI_NurbsConvert nurbs(testShape);
Handle(Geom_Surface) geom_Extrusion = BRepLib_FindSurface(nurbs.Shape()).Surface();
Handle(Geom_BSplineSurface) geombspline_Extrusion = GeomConvert::SurfaceToBSplineSurface(geom_Extrusion);

//Get number of control points in u/v-direction
int myNbUPoles = geombspline_Extrusion->NbUPoles();
int myNbVPoles = geombspline_Extrusion->NbVPoles();

//Get the control points for the spline surface
TColgp_Array2OfPnt aPoles(1, myNbUPoles, 1, myNbVPoles);
geombspline_Extrusion->Poles(aPoles);
}

Ok. The next step is to export the control point positions (poles), the uKnots and the vKnots and so on. I can do this and it works fine. But my problem is that I don't want to construct the "whole" spline surface, but only the "trimmed" surface.
I know that each TopoDS Face has a "loop" of TopoDS Edges which describe the "trimmed" surface.
My code looks like this (e.g.):
 

TopoDS_Shape testShape = myIgesReader.Shape(1);
TopoDS_Face testFace = TopoDS::Face(testShape);

Handle(Geom2d_Curve) a2DCurve;
TopExp_Explorer anExp(testFace, TopAbs_EDGE);

for (; anExp.More(); anExp.Next()) { // For each edge:

TopoDS_Edge anEdge = TopoDS::Edge(anExp.Current());

Standard_Real First, Last;

a2DCurve = BRep_Tool::CurveOnSurface(anEdge, testFace, First, Last);
}

But I don't know how to use this information for my spline surfaces?! Is there a function that calculates if a given (u,v)-point lies inside the bspline surface (and inside the corresponding loop of edges)?
Maybe someone could give me a hint how to solve my problem?!
Thank you very much for help!

Kind Regards,
Pia