Seems easy but I have some added difficulties;
-The surface is not planar of course
-My curves are all different
-The feature can be either a BlendSrf or a LooseLoft
The curves look like that:
The light blue curve is on a surface offset from the base surface, the light green curve is on the base surface.
Any idea how I should approach this?
Sample.3dm (711.7 KB)
Hello
I am not really sure of what you want.
Here there is a projection of curves on BREP following the Y direction.
Then curve on lower or upper BREP are sorted to make a Pair
Then a loft is done with these 2 curves
Then an extrusion is done to be able to cut the lower and upper BREP
project on brep.gh (261.3 KB)
Bonjour Laurent,
Thanks for taking the time!
It’s close but I think that may not be possible… There’s too much distorsion in the loft, I would need to rework the curves.
And since I need the surface to connect smoothly with the top and the bottom surface, there would be more steps.
I’ll take the “brute force” approach; trim holes on the top surface and keep the islands on the bottom surface and then create a BlendSrf between them. Since the inside and outside curves are pretty close, I have to add a lot of control shapes and tweak them.
Only a couple of days of work to complete this, I won’t die! 
I also tried creating a black-and-white image of the pattern, blurring the edges to smooth them and then using Heightfield but I couldn’t get enough resolution.
Hi, I was required to do a similar pattern with this s-section on a double-curved surface years ago.
What I did is the following:
I was not projecting curves on the surface, but a 6*n surfaces on that target (= the future “s-blends”). Now you are asking on how I projected a surface on another surface?!
I don’t remember that in detail, but I remember several approaches.
A.) You approximate the surface by moving the cps in projection direction until several test points satisfy a threshold (iterative). It is important not to add new cps (= order must stay 6 in inner direction)
B.) You project your control-point columns and rows as curves and use a similar algorithm like the “coons-patch”, to recreate a surface out of it.
C.) You use surface morph with refitting to 6*n surfaces. (this can be too imprecise)
D.) Use another CAD system for that (e.g. Icem Surf)
Once you projected the surfaces on your target surface, you do the same on the offset. Then you take the first 3 cps from one surface and the other 3 of the offset, and you are done. If you worked precisely, you don’t need to rematch the s-blends to each other. Tangent deviation should be within tolerances. (It is also important that the outline curve sections are matched at least g2, better g3 and your target and offset surface is clean and light! Use Bezier/Single-Span curves and surfaces if possible)
Hi Tom, I think I understand your workflow but it makes me think of a simpler way.
I could just create the complete pattern (trim top surface, trim bottom surface, BlendSrf between the two and repeat for the ~25 shapes) on a planar surface, then array to cover the entire area, join everything.
Then simply Flow this poly surface onto the curved surface. It’s about 1/10 the work!