Base camo values were hidden by game developers. So they were determined experimentally on the beta-test client. In the overview there are camo values for vehicles with top turrets and top-cannons.
According to game developers max spotting distance is 445 meter. But the view range of some vehicles by applying of all bonuses such as skills or equipment could be more than 445 meter. In that case this restriction is still in force, but such vehicles will have better chances to spot enemies withing 445 meters. Also there is a minimal distance of 50 meter. You will always spot enemies, which are closer as 50 meters to you. I think it depends on complexity of spotting-detection algorithm on that distances.
Camo values from the overview will be applied to observer's vehicle view capability, reducing his spotting range of a target vehicle. Therefore, it is much more difficult to spot some tank destroyer with camo value of 30 as a Maus tank with camo value of 1,4 on same distance.
Each vehicle has several view ports and outer shape points. A vehicle is considered as spotted if there is a line of view from view ports of the observer vehicle to outer shape points of target vehicle, assuming distance (incl. camo value of target vehicle) and bonuses/penalties. Therefore, it is not needed to completely hide a vehicle in a bush, the cannon for example has no shape points and couldn't be spotted by enemy.
Overview of view ports and outer shape points.
view port on the cannon basement can rotate with a turret.
The spotting conditions are checked continiously on game server. Time intervals for checks are:
Camo value of a particluar could be calculated with following formula:
camo value = (observer view range - spotting distance) / (observer view range -50)
camo value couldn't be more than 1. The more camo value some vehicle have, the closer distance is needed between observer and this vehicle to spot.
with camo value of a vehicle you can calculate spotting distance:
spotting distance = observer view range - camo value * (observer view range - 50)
Spotting distance is normally smaller as calculated on that formula because of another camo bonuses such as bushes, camo net and others.