@article{TIMM_2009_15_3_a1,
     author = {V. I. Berdyshev},
     title = {Object visibility for an observer with inaccurately given coordinates},
     journal = {Trudy Instituta matematiki i mehaniki},
     pages = {21--28},
     publisher = {mathdoc},
     volume = {15},
     number = {3},
     year = {2009},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TIMM_2009_15_3_a1/}
}