This is the code you posted today with your extra code deleted, leaving your new test curves and my code (version Convex Curves_2025Apr12a.gh ?). Looks basically OK to me?
The loops in your first post today came from your extra code, not mine.
The three shapes marked are not forming the intended way. Some of the concave curves are filleting rather than the convex ones. Which was the issue which I discovered. RenĂ©âs definition seems to address this issue.
The problem is pretty obvious when you look at it this way; enable preview on the Planar component (orange group) and notice that some planes have their Z direction (blue axis) pointing up and others point down.
There are several ways of dealing with this but⊠meh.
Oh ok, that explains it, Iâll probably have to recheck my orientations, thank you
I added the yellow group at the top to flip some curves, so all planesâ Z axis point up.
I just realized that using unit Z for comparison, as I did in the yellow group, might compromise the intent to handle polygons on any arbitrary plane. 
I just donât really care about this anymore, itâs been too long.
P.S. This hot pink group rotates the curves in either the XZ or YZ planes. It clearly shows that using unit Z for comparison works most of the time UNLESS the curves are rotated exactly -90 or +90 degrees, where it fails.
I used a similar rotation hack 12 days ago, but itâs possible to easily rotate beyond -90 or +90 degrees without noticing, unless you set the sliderâs âEdit SnappingâŠâ feature, as I did now.
Instead of fixing the problem, I created a RotateXYZ cluster in the hot pink group to rotate geometry in all three primary planes at the same time; XY, XZ and YZ
Thank you! This works really great and have a clear listing of convex and concave and works great with the loops.
Jokes aside, I think you always meant to fillet the concave curves 
Still Martin gave you the hint from the start. If curves are planar, regardless of orientation, using their native/found plane + the convex hull is enough.
Also, in my attempt you had both the convex and concave curves as well, I just didnât make it pretty (sorry).
I should probably quit fooling around with plane rotation and fix the issue I mentioned yesterday.
But creativity doesnât always work that wayâŠ
Instead of rotating geometry in three standard planes, this version borrows from an old idea, the AzAlt (Azimuth Altitude) cluster.
