title: Border points from point set
body: <p>I have an unordered set of two dimensional points, being the result of a image segmentation. The points when drawn together in a bitmap are a contigous region.</p>
  
  <p>I'd like to know which points are in it's (region) border. The region might be concave, so this has ruled out <a href="http://en.wikipedia.org/wiki/Convex_hull_algorithms" rel="nofollow">Convex Hull</a> to me. It also may have "holes" in it (ie. internal and external borders).</p>
  
  <p>There's a good (> 10k) number of points. I tought about using a (non recursive) floodfill like search, adding the border points to a vector. This would also create me a problem to "separate" internal and external border points, if a internal border exists. Is there a better algorithm?</p>