Pilou,

You could use curves/rectangle followed by construct2/planar, or
alternatively add these nodes to nodes/extension folder:
http://moi3d.com/forum/index.php?webtag=MOI&msg=7777.1710

I want to overhaul the node libraries but it will be a major project
for which I don't have time for in foreseeable future.

James
https://www.instagram.com/nodeology/

Perfect!
(added the "Shapes" files .js! )

James - Wow one small Node request so many tangles true mastery in the NODE world works great had a quick play with more complex input shape will play some more and put it through its passes. Pilou thanks for the bread crumb trails in updating NODES to get it to work.

Here is quick play

Cool exploration of form!

Pilou - random experiments as inspiration.