Extract the data associated with the indexed NURBS surface control point.

Input parameters:

1. Sf → Surface for control-point data extraction.
2. Ui → U index of control point.
3. Vi → V index of control point.

Output parameters:

1. Pt → Location of control point.
2. Wg → Weight of control point.
3. Gr → UV coordinate of greville point underneath the control point.