CompuServe Messages

Hey, thanks for the compliments Eric. << Could you explain what NURBS is and how it is different from Bspline patch modeling? >> Whew ! That's tough, without explaining spline types, etc…..also I'm no mathematician, but here goes from a user's point of view. First of all, there's various types of curves distinguished by their individual characteristics and these various types of curves can define patches named after them. You can model freeform using these control curves along with various functions to assist you, and define surfaces, patches, etc.. That's a freeform modeling approach. With a patch modeling approach, you start out with one or more types of pre-defined patches (sorta' like grids made of spline curves & their CV's as opposed to polygon vertices & edges), and then use the CV manipulation/deformation tools to form the patch into some object. NURBS curves (and I suppose, Bezier) are types of B-Spline. B-Splines can be classified as rational, uniform & non-uniform. A NURBS curve is a Non-Uniform Rational B-Spline, and is generally the most sophisticated curve to work with. The "non-uniform" term comes from the fact that you can construct curves with non-uniform knot spacing. The knotpoints I suppose are the points at which the individual curve segments are joined into the composite curve you define by defining the control lattice with control vertices. The rational term comes from the way they are defined mathematically – as a RATIO of two polynomials. They are "better" than Uniform B-Splines because: 1) They interpolate better through control points… 2) Certain types of curves such as true circles can be constructed… 3) They incorporate "weighting" as an additional local shape controlling feature, allowing more subtle & precise curve construction. Bet you're sorry you asked me now, huh ? <G> That's absolutely as succinct as I could put it, sorry. Regards, BILL