How can I determine whether an arc is clockwise or anti-clockwise? I have 3 points on an Arc - Start, MidPoint & EndPoint.
I also know the Radius and the Center.
How can I determine whether an arc is clockwise or anti-clockwise relative to it's Center?

This should do it, assuming you know the Cartesian co-ordinates, x and y, of the start and end point:
direction = ( ( ( arctan(y1/x1) - arctan(y2/x2) ) > 0 ) ? clockwise : anti-clockwise
