which should eventually be a six-sided closed solid, but the top side is not bound by a planar curve,
so that I can’t use that functionality.
I’ve tried to define a point in the center and radially created curves to the control points of the adjacent surfaces, in the hope that I could loft it this way. The lofting worked, but the edges didn’t match.
Since the opening consists of 4 curves, I tried to create the surface with the EdgeSrf-command, which looked good, but still didn’t result in a closed surface (although I don’t know why).
Edit:
On a second try, the EdgeSrf-way worked. But still, is there a reliable alternative e.g. for when I don’t have a 4-sided bounding curve?
I see that, Patch does not match the edges. Who knew?
In that case, I would extract all the edges with DupEdge. Then join all edges into 4 curves (up to you how to join them) and run the EdgeSrf command on the 4 joined curves.