How to decrease a surface's degree?

Hi,
you need

Handle_Geom_BSplineSurface nurbs_surface = new Geom_BSplineSurface(poles,uknots, vknots, umults, vmults, UDegree, VDegree,IsUPeriodic, IsVPeriodic);

degree = nurbs_surface->GetDegree(); // degree = degree + 1 or +2 ... +3
nbKnots = nurbs_surface->getNBKnot();

if degree = degree + 2 -> Index + 2 and insert new knots or Multiplicities

nurbs_surface->Setknot(Index, knots);// new Knots

Please read the help

//! Modifies this BSpline curve by assigning the value K
//! to the knot of index Index in the knots table. This is a
//! relatively local modification because K must be such that:
//! Knots(Index - 1) < K < Knots(Index + 1)
//! The second syntax allows you also to increase the
//! multiplicity of the knot to M (but it is not possible to
//! decrease the multiplicity of the knot with this function).
//! Standard_ConstructionError if:
//! - K is not such that:
//! Knots(Index - 1) < K < Knots(Index + 1)
//! - M is greater than the degree of this BSpline curve
//! or lower than the previous multiplicity of knot of
//! index Index in the knots table.
//! Standard_OutOfRange if Index is outside the bounds of the knots table.

// formel
nbKnots = (degree + 1) + nbControlPoint

Best regards
Rabih