Thanks so much for your reply, and for all the other generous replies on this thread, so appreciated, all of you!!!

I should have mentioned that ultimately I’m going to want to compare curves of arbitrary closed shapes, so this trick for circle comparison won’t apply in that case.

Is the easiest thing in this more general case to convert the circles into Breps? In the attached, I convert to Breps, and in order to check whether they intersect, I use Rhino.Geometry.Brep.CreateBooleanIntersection (perhaps this is my first mistake?).

Should I expect to get a null when there is no intersection (or is the lack of intersection not the same thing as “failure”?).

Commenting out either of these two lines shows that this code isn’t quite correct (because the results of the test later on are always the same):

//Point3d myPnt2 = new Point3d(10, 10, 0);

Point3d myPnt2 = new Point3d(3, 3, 0);

Any pointers on how to check for intersection between two Breps?

Update: I think this may be the method that I want, but haven’t been able to find sample code, and am confused about proper way to call: https://developer.rhino3d.com/api/RhinoCommon/html/M_Rhino_Geometry_Intersect_Intersection_BrepBrep.htm

Thanks again, MichaelbrepIntersection.gh (6.1 KB)