title: calculating alpha shape (concave hull) in Java
body: <p>Using Java, I would like to calculate the <a href="http://en.wikipedia.org/wiki/Alpha_shape" rel="nofollow">alpha shape</a>: given a set of 2D points, I want to find a list of polygons with minimal area that contain all the points. <a href="http://www.cgal.org/Manual/3.2/doc_html/cgal_manual/Alpha_shapes_2/Chapter_main.html" rel="nofollow">Here</a> is some more information. A pure Java solution would be ideal. Code that I can port from other languages to Java would be fine. I'd rather not use a native wrapper. An explanation of the algorithm that I could implement with reasonable effort would also be fine.</p>
  
  <p>What I really need are the triangles that make up the alpha shape polygons, so extra credit for that.</p>