Question

I need to calculate angle (A) in an oblique triangle in a large set of images in Matlab (R2012a). I know all of the 3 endpoint(pixel) coordinates of every triangle. Can I find out the angles of the triangle by using the endpoint coordinates only (independently of the image) or will I need to find out the length of all the sides and then apply the law of cosines for every triangle ? http://en.wikipedia.org/wiki/Law_of_cosines
Thank u for your help, I am new to Matlab and trigonometry!

Answer 1

The simplest way I can think of is to use the dot product. Try

  a=p1-p2;
  b=p1-p3;
  A = acos(dot(a,b)/norm(a)/norm(b));