title: Is there a better alternative to a convex hull to use in graph highlighting?
body: <p>I'm working with a graph, where I need to highlight subgraphs. The graph is in 2D. Right now, I generate a set of points from bounding rectangles of all objects that need to be highlighted, and find a convex hull of these points, like this:</p>
  
  <p><a href="http://i.imgur.com/eBWYJ.png" rel="nofollow">Convex hull</a></p>
  
  <p>However, this doesn't work that well, since a convex hull can potentially have huge empty gaps in it. If there were another subgraph going through that empty space, it would incorrectly represent two graphs intersecting.</p>
  
  <p>I've been playing around with different algorithms, but I can't find the one that works reliably and would produce desired results. The best I've come up with is this:</p>
  
  <p><a href="http://i.imgur.com/T5W3O.png" rel="nofollow">"Deflated" Convex hull</a></p>
  
  <p>...but it's unstable and very hard to debug. Before I dive back into it, I was wondering if there are any well-known algorithms to shrink-wrap a set of points. If you were to represent a convex hull as something made of an elastic material, imagine if the air was sucked out of the graph, so the empty areas of the convex hull would cave in. </p>
  
  <p>Are there any well-known algorithms to do this, or is this problem too specific?</p>