“Every contemporary CAD system“, says this article, “uses tolerant edges“. The explanation is worth reviewing, if only to understand why finite precision is essential in NURBS based modeling. It’s a shame that not many CAD user-interfaces make these tolerances explicit to the user, since they can lead to all manner of errors.
The article explains why TransMagic’s repair functions can do exactly what they’re intended to – and still leave the part with tolerant edges. This 17-page article from 1991 is a useful reference if you want to dig deeper, while this is pretty good too.
