Hi Fabrisol- see if the attached file helps at all - the closed elliptical curve is split at the lines; each surface is an EdgeSrf of three curves- a section of ellipse and two lines, (Not the ones that end on a point at the ellipse, of course, they are made the other way round) Choose the side where you want the center isocurve first (i.e. the ellipse segment) when picking the curves for EdgeSrf. The surfaces are joined, and the whole thing is split (red and blue), and then one of them unrolled. Am I close?
Rectangle to round transition_Maybe.3dm (111.2 KB)
-Pascal