Visibility rules

[condor]

This tread is intended to gather some advice and insights on guidelines for general visibility rules, that are dispersed throughout rules books. I miss a structured set of instructions when planning realistic patrols, search operations, castle walls manning, etc.

I don't know if this has been discussed elsewhere, but I could not find it.

These general visibility rules could address some of the following questions:

1) How far can a man spot another man moving on the grass, assuming he is on a castle wall, like 15ft above the ground, and under perfect light and weather conditions? Or, put in other words, on average, how far a person with Per of 10 could roll against 12?

2) How far can a person recognize a friend in the same conditions?

3) How far can a soldier keep track of another one in differente environments, like a deciduous forest, or a night grass field?
It would help to answer questions of how much land ten man can sweep with a search team in one hour.

Thanks in advance!