Region Grow Circle
This command extracts a circle according to seed points and visible objects.
Requirements
To extract a circle, launch the command and click a seed on objects.
You can force the center, the normal or the radius :
Set the Extraction tolerance.
Click a seed point.
to click a 
to define a Notes
Once a seed point is clicked, the computation is launched. You can cancel the current computation by pressing ESC or by clicking another point.
Sometimes, when you compute a circle, an incorrect extraction may occur with the point you click if, at this place, the noise disturbs the local curvature evaluation or if only a part of the circle is present. In this case, click a new point to replace the current seed point.
The Extraction tolerance corresponds to the extraction of the plane which contains the circle (Extraction performed in two steps: plane and contour extractions).