The following texts provide more detailed information on NURBS curves and surfaces:
Bartels, R., J. Beatty, and B. Barsky, An Introduction to Splines for Use in Computer Graphics and Geometric Modeling. Los Altos, Ca.: Morgan Kaufmann, 1987.
Farin, G., Curves and Surfaces for Computer Aided Geometric Design, 2e. San Diego, Ca.: Academic Press, Inc., 1990.