From what I learned and understood about nurbs, only rational splines can model conics.

I think this is even the only reason why they were created.

NURBS = Non Uniform Rational Basis Spline

A nurbs without weights is not rational, so it could be called a NUBS.

Same for a Bspline whose parametrization is not uniform.

Off-topic :

Personally, What I would really like to know is what makes "uniform" parametrization so special that all other splines get called Non-Uniform ?

I mean : why a Uniform / Non-Uniform segregation ?

Why not Chord-Length / Non-Chord-Length ?

Or Arc-Length / Non-Arc-Length ? ( this one would make sense to me )

Do you say this because of the number of inner lines ?looo wrote: ↑Fri Sep 08, 2017 6:43 am1. looking at pictures of rhino [1], it seems the degree of the flat faces is higher. So maybe there is a nurbs-base with a higher degree which can give an exact solution. I think it is possible to find such a nurbs-base which can exactly map some poles to the derivatives of the spline....

I have never used Rhino, but I suspect them to be only isocurves, for visualisation purpose, with no relation with degree or knots.

I think I faced a similar kind of problem recently with a ruled surface that was not looking good : My 2 curves don't have a good matching parametrization.

In that kind of cases, it is probably possible to go through a reparametrization function, to map a user-defined parametrization to the real curve parametrization.

Werner will surely be able to bring more light on all this ...

EDIT : cross-posting. He did