NURBS and Span

 From:  Michael Gibson
5897.6 In reply to 5897.1 
Hi Claas, or I guess looking into it a bit more, the single span thing you're referring to is more about certain Alias tools only working when curves are touching each other at precise locations like they have to all meet up at knot locations?

Some limitation like that has more to do with the specific mechanism that whoever implemented that command decided to use, certain kinds of mathematical surface construction techniques might have requirements like that, but it's also often possible for there to be different approaches for doing the construction that just go about it in a somewhat different way that does not happen to have the same limits, possibly by doing something like a fitting process.

Sometimes the limited way may have some special benefit like the surface generated by it has the exact same control point structure as the original curves used. But the bad part is that if the command only works with a very specific kind of structure it means you have to know quite a lot of details about how NURBS work before you'll be able to really be able to use it very well...

Some of the other focus on single span surfaces might come from automotive people from an ICEM Surf background, which is a surfacing system that focuses only on using Bezier surfaces which are the equivalent of single span NURBS surfaces, and focuses more on manipulating surface control points quite a bit. It's again a highly specialized tool with a high learning curve and cost involved...

- Michael