Hi Hans,

re:
> Even though I still don't think I understand why there is no surface like you stated?

I meant that in your post you showed this:


Were those meant to be planar cross-section surfaces? Those are the ones you don't have in your .3dm file. But it sounds like there is a Grasshopper method to generate those for you automatically?


> For a calculation of the center curve I am thinking of first slicing the tube/solid/shape in little pieces.
> Then find the midpoint for each piece by integration. Then connect the midpoints to a single center
> curve and finally smooth out the edges if need by some smooth algorithm.

Sounds good - I thought that you were asking for a fully automated calculation.


> Yes exactly - well a bit of both. My idea is that I can cut out an interesting shape and then change the surface on that shape

Ok, but to get a tube like that another approach that would be simpler could be to project just one curve onto your solid and then sweep with that rather than cutting out a channel with 2 curves:

For example, just one profile curve:



Construct > Curve >Project to project it onto the solid:



Construct > Sweep using the projected curve as the rail curve for a one-rail sweep:



- Michael