Alpha Hull?

Following on from last time I have now implemented removal of all edges in the alpha shape which are longer than σ. I have then merged the shape with the previous mesh resulting in:

Im not really sure if this is just an expected result and simply because of a bad value of σ or if there is a bug.

Next I need to find a way of removing the interior polygons, Im thinking that I will need to do something like:

1) build a list of edges from the list of faces (only storing connectivity information to the face that uses it)
2) check for edges with more than two instances
3) use the face normals of all the attached faces to determine the outermost pair

This should leave me with multiple disconnected sets of polygons which I can probably pick between using the bounding boxes, the alpha hull being the largest.