Technical Details
Interpolated splines are always degree 3.
If control points are specified and the NURB spline uses Uniform or Non-uniform knots, then the degree field can be used to control the degree of the spline. The maximum degree is 20 and the minimum degree is 1. The minimum number of control points in a Uniform NURB spline is the degree of the NURB spline plus one.
If the NURB spline uses Bezier knots, then the degree is automatically the number of points in the controlling polygon minus one, and this value is ignored. Since the maximum degree is 20, the largest Bezier spline that can be created will contain 21 control points.
This specifies the complexity of the equations defining the NURB spline. The higher the degree, the number of points that can be interpolated by a single segment increases. Also, with a higher degree the spline tends to stay away from the control polygon (considered smoother). Higher degree splines have problems of different kinds (numerical instability and oscillations). Even numbers are worse than odd. Time to work with a spline is inversely relative to the degree. In general many geometric modeling applications limit the degree of the splines to be 3 although degrees of 5 through 8 are not uncommon. SURFCAM limits the degree of a NURB spline to 20.
A NURB surface has two degrees; one along the U direction and the other along the V direction.
The degree of a NURB spline must be at least one less than the number of control points. In the case of a NURB surface, the degree in each direction must be at least one less than the number of control points in that direction. A NURB spline of degree 1 can be used to represent lines and polylines. SURFCAM splines can be accurately represented by NURB splines of degree 3.