Control Points

Every NURBS surface, like a NURBS curve, has a set of control points which control its shape but which do not necessarily lie on the surface. The concepts describing NURBS curves can be extended to a NURBS surface if applied to the isoparametric curves of the surface.



The broken line joining the control points of a curve is called the control point polyline or polygon or defining polyline. A numeric value, called the weight, is associated with each control point (see also the article on control points of curves). Initially, the value of the weight is 1, but you may change it at any time. If you increase the weight of a control point, the surface moves closer to the control point; if you reduce it, the surface moves away from it. If you move the control points, the shape of the surface changes accordingly.