title: Ordering CONCAVE polygon vertices in (counter)clockwise?
body: <p>I have a set of disordered vertices that may form a concave polygon. Now I wish to order them in either clockwise or counterclockwise.</p>
  
  <p><a href="https://stackoverflow.com/a/13935419/2106753">An answer here</a> suggests the following steps:</p>
  
  <ul>
  <li>Find the polygon center</li>
  <li>Compute angles</li>
  <li>Order points by angle</li>
  </ul>
  
  <p>This is obviously only for convex polygon and will fail when the points form a concave one.</p>
  
  <p>How may I do this to a concave one?</p>
  
  <p>I am using Python, but welcome all generic answers.</p>