Look at my answer in the "line from center point" request, your answer about c-lines helped me.

Okey cool, but in your example you have a circle, you can use the quad of the circle to help you.
Show me with the "S" letter that Pilou showed, how do you do it fast?
A bounding box command would be perfect yes :) Even better if it works in 3d too :D
And also if it works with multiples objects, just like the scale/rotate gizmo that show up when you select objects.

Thanks again for the explanations.