title: Algorithm for polygon intersection
body: <p>In my code, I'm generating a polygon for the description of a region.</p>
  
  <p>This polygon is created by a semplification of a 34000-vertices polygon, given at the beginning of the code.</p>
  
  <p>But in the semplification I have to use, I've found this problem: sometimes it generates intersections of sides. I'm asking for algorithm useful to detect intersections.</p>