Surface between 3 curves

[vano_artful (V@no)]

Hello.
I’m trying to create a surface between 3 curves, where the middle curve (blue) is partially protrude creating a “bulge” (imagine a sheet of canvas stretched between red and green; and blue pushes out in the middle)

So, I think I need the following:

1. I’m using Sweep2 because I can control the “flow” of the surface between uneven curves, but it requires at least 3 sides, so I guess I need to split red and green curves into pieces for that
2. Next, I need to find where blue curve would intersect:
   
   
   When I attempt split blue curve with that surface, it splits it away from the surface:
   
   
3. I need to split red and green at the points where if I draw a line between these curves, it would touch blue curve too. This step I have no idea how to achieve.
4. once red and green curves properly split, I then can create surfaces between green->blue and red->blue in the middle and green->red on each end, creating watertight surface.

So, this is my logic and so far I’m really struggling with step 3, how do I draw a straight single line touching all 3 curves (preferably vertically ortho from front view)? (in parametric software it would be a breeze by constraining a line to all 3 curves)

Or is there a better way to achieve this?

Thank you.
3curves_surface.3dm (112.1 KB)

[Lagom]

The curves consist of multiple joined curves, which are overly complex, and are very wobbly, with an odd curvature. Also the left/right symmetry is off, but this might be intentional? Maybe you have a sketch or mock-up photo of what you are trying to achieve?

With simple single span NURBS curves, you get simple surfaces, and then you can fillet or otherwise construct the transition where the “tarpaulin” goes over the central curve of the three. I’m only guessing because there’s no indication of what your final “shape/thing” shall really look like, or why the curves are spliced together and rather messy.

[jeremy5 (Jeremy)]

@vano_artful

how do I draw a straight single line touching all 3 curves (preferably vertically ortho from front view)?

You can do this with your three lines but you need a ‘better’ surface between the outer pair to do so. Here’s how:

1. Rotate the lines in the perspective view to get a feel for roughly where the curves line up.

2. Create an array of planes large enough to encompass the three lines across the place where things line up (the planes must be parallel to the YZ plane; setting the planes an inch apart will turn out to work here):
   

   

3. Create intersection points between the planes and the outer lines:
   

   

4. Draw lines between the pairs of points:
   

   

5. Loft the lines (ignore the area in the middle where eyeballing indicated the curves won’t line up):
   

   

6. Find the intersections between the surfaces and the blue line:
   

   

7. Create a YZ plane centred on each intersection point:
   

   

8. Intersect the YZ plane with the surfaces to create your desired lines between the outer lines:
   

   

3curves_surface 001.3dm (286.8 KB)

HTH
Jeremy