CGAL users discussion list

Hi!
I would like to extract the outer and inner boundary (if holes, islands 
respectively are given) of a point cloud.

I calculate the 2d alpha shape. How can I get a list of coordinates belonging 
to the outer boundary of the segment (the order of the points should follow 
the line)? How can I distinguish between island points and points on the 
outer boundary?

Thanks in advance,
Bernhard