I’m trying to construct a curve that needs to be a tangent at both Ends. The wrinkle is, that the left End needs to be tangential to Closed curve-B at some unknown location, probably within the circled area of the screenshot.
I’m sure I’ve done this before successfully in Rhino (only) but am having trouble recreating it in Grasshopper.
I expect it’s fairly simple. Adjusting an input for the curve would affect the location of the landing point.
It might be “simple” but your explanation isn’t clear and you didn’t post a file. 
OK, is this any better?
As above, I can create the two-End tangency readily enough in Rhino (only) using ‘Conic: Tangent at start, end”. But I’d like to do it all in Grasshopper. Which is a file I don’t have.
As an alternative, is there a Gh tool that is the equivalent of, or overlaps with, that Rhino Conic Command please?
I am DONE with threads that don’t post relevant GH or geometry, and have unclear descriptions, especially when the word “simple” is used.
Not sure - don’t think so. Or, the ‘equivalent’ is probably a more involved method to create a NURBS curve applying some ‘math principles’ to calculate weights and what not. I am already doubting what I am typing because I actually don’t know so I’ll stop pretending 
However, and meanwhile, if your ‘landing’ point (I interpret such point is your ‘red’ annotation saying ‘A–line, with Point at left end’) is indeed the ‘left end’ of a straight line, then the direction of that line helps in the creation of a ‘quadratic bézier curve’ to approximate the conic-tangent command option in Rhino.
The BzSpan component asks for a tangent at start and at tangent at end.
The line on which the landing point lies at its end can be the direction for the end tangent.
You didn’t post your rhino curves, so I made a random closed curve to test this idea in case it helps:
pseudoconic.gh (16.3 KB)
Cheers!
René,
This certainly helps and thank you for taking this trouble.
PseudoConic works and provides continuous, full, adjustable solutions.
(I should have mentioned that the intermediate curve doesn’t need to be conic, only that it were tangential at each End, and that the closed curve could be any closed curve that is not a circle.)
And thank you for interpreting my poorly framed problem so generously. Your patient and detailed discussion has also given me effective leads on many related questions, that have probably helped others too.
Given that the Rhino command (conic: tangent start, end) involved only six simple steps—included the ability to set the curvature (Rho value)—I had wrongly guessed that Gh had one or two Components that did a similar job. I’m no longer a beginner at Grasshopper, but I see there’s lots to learn!
