@article{JGG_2006_10_1_JGG_2006_10_1_a3,
     author = {W. M. Pieper },
     title = {Multifocal {Surfaces} and {Algorithms} for {Displaying} {Them}},
     journal = {Journal for geometry and graphics},
     pages = {37--62},
     publisher = {mathdoc},
     volume = {10},
     number = {1},
     year = {2006},
     url = {http://geodesic.mathdoc.fr/item/JGG_2006_10_1_JGG_2006_10_1_a3/}
}