Hi Karsten

Maybe I'll have a look this weekend.

(I could not get PDF save of your ccc.3dm to print. It just did outline(?)
So I just get a screensave.)

I'm wondering, if the curve is planar, why not set it as cplane, and intersect the perpendicular bisector lines through the
two centerpoints of P1P2 and P2P3, to find the center of the circle from AP1, P2, P3? Is it necessary to use 3 planes?

- Brian