Joachim Gudmundsson Christos Levcopoulos Giri Narasimhan Michiel H. M. Smid Approximate distance oracles for geometric spanners. 2008 4 ACM Transactions on Algorithms 1 http://doi.acm.org/10.1145/1328911.1328921 db/journals/talg/talg4.html#GudmundssonLNS08