...of a curve drawn on a volume and that you can move on this volume?
(with constant application of all points on it)
Iso curve?

Hi Pilou, there is not really any special name for just any curve that may be drawn on a surface, that would just be called a "curve on surface" I guess.

An isocurve is a special sub-category of curves on the surface which is a curve associated with one of the U or V directions of the underlying surface. A surface is basically a continuous net of curves crossing each other in these U and V directions, and an isocurve is just one single one of that network. It's basically aligned with the surface's control point grid.

There is not any "natural" built-in method with NURBS for drawing just any arbitrary curve on a surface and then moving the curve around and having the surface follow - that can only be accomplished with a lot of special calculations.

The natural way that a surface is moved is by moving the surface's control points around - those are the most basic part of the surface's definition that can be altered directly.

- Michael

< The natural way that a surface is moved is by moving the surface's control points around - those are the most basic part of the surface's definition that can be altered directly.

Agree for a surface
so very difficult for a curve as I see :)

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

So it's more speedy to project a line from the top view to the volume (well oriented )
for have an extracted curve from the volume than draw the line on the surface (quasi impossible)

Hi Pilou, sorry maybe I have misunderstood your question completely.

I thought you were talking about projecting a curve onto a surface, then editing the curve and have the surface move with it.

But it seems you are talking about having a curve on a surface, which you can edit and that the curve stays on the surface while you manipulate the curve?

That is something that would be called a "curve on surface". It can be possible to create the curve in the UV space of the surface and then also edit it there, which means that the edited curve stays on the surface.

MoI does not currently have anything set up to make editable UV curves like that though, but maybe in the future at some point.

- Michael

< But it seems you are talking about having a curve on a surface, which you can edit and that the curve stays on the surface while you manipulate the curve?
Yes exactly (all the curve) :)