When a face geometry is represented by a `BSplineSurface` object, I can read the b-spline/NURBS data (such as knots and poles) from it directly.
But when a face geometry is represented by an `EllipticalCylinder` or `EllipticalCone` object, I *also* want to treat these as freeform faces in further processing, and thus need them as a NURBS.
Does the Inventor API provide a way to get this data in this case?
