Ullrich Köthe XPMaps and Topological Segmentation - A Unified Approach to Finite Topologies in the Plane. 22-33 2002 conf/dgci/2002 DGCI http://link.springer.de/link/service/series/0558/bibs/2301/23010022.htm db/conf/dgci/dgci2002.html#Kothe02