Matthew O. Ward
Jeffrey T. LeBlanc
Rajeev Tipnis
Computer Science Department
Hewlett-Packard Company
Sonitech International, Inc.
Worcester Polytechnic Institute
Medical Products Group
Worcester, MA USA 01609
Waltham, MA USA 02254
Wellesley, MA USA 02181
This is a reprint of the paper presented at the Computer Graphics International Conference in Melbourne, Australia, 1994.