Luca Chittaro Roberto Ranon Lucio Ieronutti VU-Flow: A Visualization Tool for Analyzing Navigation in Virtual Environments. 1475-1485 2006 12 IEEE Trans. Vis. Comput. Graph. 6 http://doi.ieeecomputersociety.org/10.1109/TVCG.2006.109 db/journals/tvcg/tvcg12.html#ChittaroRI06