Hi Pilou,

re:
> I obtain the same result than Catmull Clark if I import the OBJ at level 0 so straight lines!
> It's Moi that makes the subdivision (same result than Catmull Clark! :)

Right, that's how you want to do it.

The other result you're showing like this:


is because you're converting into smaller triangles and then trying to process that triangulated mesh as a sub-d control cage. That will make an extremely dense surface and also introduce a lot of bumpy artifacts so it's not a productive option.

- Michael