Peer-Timo Bremer Herbert Edelsbrunner Bernd Hamann Valerio Pascucci A Topological Hierarchy for Functions on Triangulated Surfaces. 385-396 2004 10 IEEE Trans. Vis. Comput. Graph. 4 http://doi.ieeecomputersociety.org/10.1109/TVCG.2004.3 db/journals/tvcg/tvcg10.html#BremerEHP04