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?

Let ${\bf s}=(s_1,s_2)$, ${\bf m}=(m_1,m_2)$, ${\bf e}=(e_1,e_2)$ be the three points. We have to check whether the triangle they form is positively oriented. Therefore compute the quantity
$$\sigma:=({\bf m}-{\bf s})\wedge({\bf e}-{\bf s})=(m_1-s_1)(e_2-s_2)-(m_2-s_2)(e_1-s_1)\ .$$
If $\sigma>0$ the arc is counterclockwise, if $\sigma<0$ the arc is clockwise.
