Compute the relative orientation of 3 points.

   CCW = isCounterClockwise(P1, P2, P3);
   Computes the orientation of the 3 points. The returns is:
   +1 if the path P1->P2->P3 turns Counter-Clockwise (i.e., the point P3
       is located "on the left" of the line P1-P2)
   -1 if the path turns Clockwise (i.e., the point P3 lies "on the right"
       of the line P1-P2) 
   0  if the point P3 is located on the line segment [P1 P2].

   This function can be used in more complicated algorithms: detection of
   line segment intersections, convex hulls, point in triangle...

   CCW = isCounterClockwise(P1, P2, P3, EPS);
   Specifies the threshold used for detecting colinearity of the 3 points.
   Default value is 1e-12 (absolute).

   Example
   isCounterClockwise([0 0], [10 0], [10 10])
   ans = 
       1
   isCounterClockwise([0 0], [0 10], [10 10])
   ans = 
       -1
   isCounterClockwise([0 0], [10 0], [5 0])
   ans = 
       0

   See also
   points2d, isPointOnLine, isPointInTriangle, polygonArea

   References
     Algorithm adapated from Sedgewick's book.

Package: matgeom