Sort points by angle from given axis?

Question

How can I sort an array of points/vectors by counter-clockwise increasing angle from a given axis vector?

For example:

Answer 1

If S is an array of PointF, and mid is the PointF in the centre:

S = S.OrderBy(s => -Math.Atan2((s.Y - mid.Y), (s.X - mid.X))).ToArray();

will sort the list in order of rotation around mid, starting at the point closest to (-inf,0) and go ccw (clockwise if you leave out the negative sign before Math).