An important activity that must be done previous to installing some types of telecommunication
Practically, it means that the telecom antenna
s or laser
s or whatever
s must "see" each other.
In trivial cases, this is done by climbing on the roof and using a pair of binoculars.
The analysis is complicated by the fact that microwaves do not really propagate as visible light does: some things may act as microwave "mirrors" (for example: an array of power cables), even if they are approximately transparent.
You should also factor in the fact that all microwave antennas emit most of their power on a primary lobe, and sprinkle some in secundary lobes: that power can be reflected (and refracted), and it can give rise to interference with your primary lobe.
Large scale line of sight analysis in urban areas can also be done by software.