U. Brandes, and T. Willhalm. Proceedings of the symposium on Data Visualisation 2002, page 159--ff. Aire-la-Ville, Switzerland, Switzerland, Eurographics Association, (2002)
A. SAKA, and M. IGAMI. IV '07: Proceedings of the 11th International Conference Information Visualization, page 453--458. Washington, DC, USA, IEEE Computer Society, (2007)