title: Determining ordering of vertices to form a quadrilateral
body: <p>Suppose I have 4 vertices in 2D space.  Does anything know of an efficient algorithm which will give me an ordering of the vertices which corresponds to a simple quadrilateral?  That is, it will label the vertices <code>1, 2, 3, 4</code> so that if I follow <code>1-2, 2-3, 3-4</code> I will have traced a simple (i.e. non-intersecting) quadrilateral.</p>
  
  <p>Just providing the name of a standard algorithm which I can google would be fine. </p>