Kenneth L. Clarkson David Eppstein Gary L. Miller Carl Sturtivant Shang-Hua Teng Approximating Center Points with Iterated Radon Points. 91-98 1993 Symposium on Computational Geometry http://doi.acm.org/10.1145/160985.161004 db/conf/compgeom/compgeom93.html#ClarksonEMST93