Pankaj K. Agarwal Mark de Berg Jie Gao Leonidas J. Guibas Sariel Har-Peled Staying in the Middle: Exact and Approximate Medians in R1 and R2 for Moving Points. 43-46 2005 conf/cccg/2005 CCCG http://www.cccg.ca/proceedings/2005/19.pdf db/conf/cccg/cccg2005.html#AgarwalBGGH05