Hi Stefan, the main problem with Bezier patch modeling is the same as with Bezier curve modeling which is that it's difficult to get G2 continuity across patches or curve segments without constraining everything to be in the symmetrical handle editing mode.

That's basically the fundamental reason why NURBS curves and surfaces were invented, to have a way to generate multiple bezier patch spans from a longer sequence of control points with guaranteed continuity between the internal spans of a single surface.

Even aside from strict G2 continuity, it's just difficult to avoid general surface shaping defects like unwanted ridges and and smooth curvature distribution using that type of patch modeling (with editing points right on the patch) method compared to sub-d.

- Michael

Hi Michael,

thank you for the detailed explanation! Now i understand why this modeling method
is not used in (more) (NURBS) software.

Regards
Stefan

about translation (language) what exactly "span" in the text above ?

Hi Pilou,

check this illustration for a definition of a span:

https://knowledge.autodesk.com/support/alias-products/getting-started/caas/CloudHelp/cloudhelp/2018/ENU/Alias-Tutorials/files/GUID-44C90759-1812-4051-85BF-072140EE6623-htm.html

Regards
Stefan

Hi Pilou,

re:
> about translation (language) what exactly "span" in the text above ?

It's basically a section of a curve that can be directly evaluated as a polynomial function (as a Bezier).

When you have a curve or surface that has a lot of points in it, it's not practical to use a single polynomial to evaluate the whole thing so there needs to be a way to chain together several of them. Part of how NURBS curves work is that it defines how these spans share points with each other so they can automatically stay smooth to each other.

- Michael

Ok very clear of what it is! :) Seems 2 different things !

But have you a word in this list https://www.wordreference.com/enfr/span
because
I have not yet satifying word in French!

Hi Pilou, well some other words that could probably be used would be "section", "portion", "segment", or "piece".

- Michael

Bonjour Pilou,

Les mots qui me sembleraient les plus proches du sens de span dans ce contexte seraient : la "portée", "l'étendue" ou la "couverture".
Lequel serait le plus précis ?

Le plus poétique serait "l'empan" pour le second, et "lamelle" pour le premier... :)

Mais c'est toujours étonnant comme l'anglais donne à un même mot une quantité de significations suivant un contexte différent!

The most poetic would be "span" for the second, and "lamella" for the first... :)

But it's always amazing how English gives the same word a number of meanings in a different context!