How to Outline Group of 2D points

Hi all, just wondering if anyone knows of a function already written (or easily edited ) to handle this problem.   I need to outline a group of 2d points (300,000+ points in most cases).  I need something similar to the convex hull algorithim, but in this case i need to be able to address concave points as well.  (So basically an outline of all the outermost points with some kind of tolerence.   (An example would be a 2d point cloud representing say the letter X.  What would be the best way to draw an outline of that point cloud X ?

Thanks!