@Article{Fitzgibbon99,
  author = "Fitzgibbon, A.~W.and Pilu, M. and Fisher, R.~B.",
  title = "Direct least-squares fitting of ellipses",
  journal = pami,
  year = 1999,
  volume = 21,
  number = 5,
  month = may,
  pages = "476--480"
}