Question

I came across this link http://www.mathopenref.com/coordpolygonarea2.html

It explains how to calculate the area of a polygon and helps to identify whether the polygon vertices we entered is clockwise or counter clockwise.

If area value is +ve, it is clockwise, if it is -nv then it is in counterclockwise.

My requirement is to identify only whether it is clockwise or counterclockwise. Is this rule will work correctly (though there are limitations as mentioned in the link). I have only regular polygons (not complicated, no self intersections) but the vertices are more.

I am not interested in the area value accuracy, just to know the ring rotation.

Any other thought on this.

Answer 1

For convex polygons:

Select two edges with a common vertex. 
Lets say, edge1 is between vertex A and B. Edge2 is between vertex B and C.
Define to vectors: vect1: A----->B
                   vect2: B----->C
Cross product vect1 and vect2. 
If the result is positive, the sequence A-->B-->C is Counter-clockwise. 
If the result is negative, the sequence A-->B-->C is clockwise.