Light sources are affixed at appropriate positions in a multilevel structure or in an obstructed environment. The light sources generate modulated light signals, such as controlled light-emitting diodes, which identify the positions of the light sources by their three-dimensional global positioning coordinates and/or equivalent representation that specifies their in situ locations in the environment. Mobile communication devices, upon receiving the light signals, can derive spatial positioning information and transmit such information to a remote location, such as an emergency response system.