Hi all - Intermediate Rhino user, but just venturing into Grasshopper, so I thought I set myself a simple form to generate. This is actually for a component I need. See image. In GH I can generate the ellipse ok, and the four curves (the x, y, and z dimensions of all these can be changed with sliders and they all stay meeting at the right places!), If I bake the ellipse plus 4 curves I can go into Rhino and just click ‘Curve Network’ and I get the form as shown. But, if I feed the ellipse and the four curves into the ‘Network Surface’ component in GH it goes an angry red and says I need a second curve … What am I doing wrong? A million thanks. Jack
Not posting your GH file 
3. Attach minimal versions of all the relevant files
A “simple form” is a box or cylinder or loft between curves. This doesn’t look simple, though you have a valid point if GH NetSurf behaves differently than Rhino ‘Curve Network’.
I couldn’t make NetSurf work either and had something else in mind than what I ended up with, which is Swp1 using four rails (“shattered” ellipse), each with two section curves, resulting in four surfaces instead of only one. 
I used four BiArc curves but any four curves should work instead.
Many thanks Joseph. My GH file attached. The complicated thing is that the vertical curves are not segments of ellipses. There is a straight line down from the two ends of the ellipse (vertical length set by slider) joined to a quadrant of a circle from the ends of them meeting at the base point. The two other curves are defined by that base point plus points defined by sliders. I can generate the ellipse and four curves that I need, just not one surfaces. I can get four surfaces using quadrants of the ellipse as curves, but these surfaces don’t then join smoothly without vertical creases. Don’t worry two much about it as it more of a challenge for me than a necessity. Thanks
Ellipse-Test2.gh (13.7 KB)
The cyan group contains the curves from your file. The yellow group(s) fix curve directions so they are all the same.
If you don’t care then why should I? Maybe you don’t want the GH file either, but someone else might.
ellipse_form_2023Dec17a.gh (15.1 KB)
1 Like
Thanks HS_Kim - that works perfectly. What I was trying to achieve (a finger ring with variable proportions) attached. I am sure this can be streamlined, but as I said I am just learning GH, so this was a fun start. Thanks
Ellipse-NEW_re.gh (25.3 KB)
In retrospect, even though it’s not what you asked for, I think there is value in the BiArc curves approach I used yesterday so will post that file here too.
ellipse_form_2023Dec16a.gh (16.5 KB)
Thanks Joseph - nice!
Jack