Line order and direction

 From:  Michael Gibson
9781.20 In reply to 9781.16 
Hi Wayne, another way you can determine the direction just using 2D points is to make a 2D triangle and then compute the signed area of the triangle:
https://www.quora.com/What-is-the-signed-Area-of-the-triangle?share=1

It will be a positive number for CCW, and a negative number for CW.

- Michael