S. van Dijk, M. van Kreveld, T. Strijk, and A. Wolff. Proc. 19th Internat. Cartographic Conf. (ICA'99), page 905--913. Ottawa, Internat. Cartographic Association, (1999)
M. van Kreveld, {. Schramm, and A. Wolff. Proc. 12th Internat. ACM Symp. Advances in Geographic Information Systems (ACM-GIS'04), page 222--231. ACM Press, New York, (2004)
E. Moet, M. van Kreveld, and A. van der Stappen. SCG '06: Proceedings of the Twenty-Second Annual Symposium on Computational geometry, page 177―186. New York, NY, USA, ACM, (2006)