I think Juan Rodriguez' programme will do that. You can get it by
anonymous ftp to 132.166.17.100 or 132.166.17.146. It may also
be possible with Jane Brown's Cambridge Crystallography Subroutine
Library (brown@ill.fr), but she's on vacation at present.
Alan Hewat, ILL Grenoble, FRANCE (hewat@ill.fr) Fax (France=33).76.48.39.06