@article{JGG_2000_4_2_a6,
     author = {G. Weiss and H. Martini},
     title = {On {Curves} and {Surfaces} in {Illumination} {Geometry}},
     journal = {Journal for geometry and graphics},
     pages = {169--18},
     publisher = {mathdoc},
     volume = {4},
     number = {2},
     year = {2000},
     url = {http://geodesic.mathdoc.fr/item/JGG_2000_4_2_a6/}
}