convert Geom_Surface in to Geom_BSplineSurface

I work with Linux. I have an compound and i extract the faces. I know the type of faces : BSpline .I want to know the NbUPoles, the NbVPoles,... I do: TopExp_Explorer ex; ex.Init(resultat,TopAbs_FACE);

while (ex.More()){ TopoDS_Face f=TopoDS::Face(ex.Current());

Handle (Geom_Surface) S= BRep_Tool::Surface(f);

//declaration d'une variable b qui est de type surface BSpline

const Handle (Standard_Type )& b=STANDARD_TYPE(Geom_BSplineSurface);

//on verifie que la face extraite est une surface BSpline

if (S->IsKind(b)) {

Handle (Geom_BSplineSurface) b1=S; cout NbUPoles() NbVPoles()

but the type of b1 and S it is not the same . What can i do?