About interactive control a circle mesh


I have create a circle mesh using a polar coordinates computation, now I want to:
(1) define some points on the circle as “control points”;
(2) pick the points and move them to stretch the mesh;
(3) when the motion is done, I can get all the coordinates of “control points”.

who can give me some suggestions, thanks a lot!

(I have tried to use “evaluator”, but bezier func can not generate a circle curve …)