Hi Pilou, yes so the problem is that if you draw or project just any arbitrary curve on to a surface, the curve is really a completely separate thing from the surface - that curve does not play any role in actually defining the shape of the surface.

So therefore, editing the curve is just editing the curve and does not automatically or naturally also edit the surface.


It is possible to do some kind of special fitting process that tries to alter the surface to pull it towards the curve, but that would require a lot of specialized calculations, it's not something that is just automatically set up in the way NURBS surfaces are defined.

- Michael