A computer-implemented method for designing a 3D modeled object, wherein the method comprises the steps of: • providing (S10), to a computer system, a NURBS surface that represents the 3D modeled object and that is defined by a grid of control points; • determining (S20), by the computer system, a grid of surface points that belong to the NURBS surface, the grid of surface points corresponding to the grid of control points according to a predetermined invertible function; • displaying (S30), by the computer system, the NURBS surface and, on the NURBS surface, the grid of surface points; • selecting (S40), by graphical user-interaction, a subset of the surface points; • modifying (S52), by graphical user-interaction, position of the selected subset of surface points, and accordingly, updating (S54) real-time, by the computer system, the surface, the update being performed according to the predetermined invertible function, characterized by : wherein the updating (S54) of the grid of control points is performed by optimizing a program that penalizes geometrical deformation of the NURBS surface, under the constraint that the position of the selected subset of surface points be as modified, wherein the program penalizes geometrical deformation of the NURBS surface by penalizing, for each respective control point, a distance between the respective control point before the update and the respective control point after the update. • providing (S10), to a computer system, a NURBS surface that represents the 3D modeled object and that is defined by a grid of control points; • determining (S20), by the computer system, a grid of surface points that belong to the NURBS surface, the grid of surface points corresponding to the grid of control points according to a predetermined invertible function; • displaying (S30), by the computer system, the NURBS surface and, on the NURBS surface, the grid of surface points; • selecting (S40), by graphical user-interaction, a subset of the surface points; • modifying (S52), by graphical user-interaction, position of the selected subset of surface points, and accordingly, updating (S54) real-time, by the computer system, the surface, the update being performed according to the predetermined invertible function, characterized by : wherein the updating (S54) of the grid of control points is performed by optimizing a program that penalizes geometrical deformation of the NURBS surface, under the constraint that the position of the selected subset of surface points be as modified, wherein the program penalizes geometrical deformation of the NURBS surface by penalizing, for each respective control point, a distance between the respective control point before the update and the respective control point after the update. wherein the updating (S54) of the grid of control points is performed by optimizing a program that penalizes geometrical deformation of the NURBS surface, under the constraint that the position of the selected subset of surface points be as modified, wherein the program penalizes geometrical deformation of the NURBS surface by penalizing, for each respective control point, a distance between the respective control point before the update and the respective control point after the update. <EOS>