H. Pottmann, T. Steiner, M. Hofer, C. Haider, A. Hanbury:
"The isophotic metric and its application to feature sensitive morphology on surfaces";
in: "Computer Vision --- ECCV 2004, Part IV", Springer, 2004, 560 - 572.
http://aleph.ub.tuwien.ac.at/F?base=tuw01&func=find-c&ccl_term=AC04969862