So, every vehicle has a "view range" and a "camo factor", both of which can be buffed when your crew levels up, and you get various upgrades.
The way cam and spotting relate is as follows:
ViewRange - (ViewRange * CamoRating)
So for example the XM800T has a rough view range of 500m and the Leopard 1 has a camo of 0.10. So the Leopard would be spotted by the XM800 at 450m in open terrain.
The white circle surrounding your vehicle on the minimap shows your view distance and can give you a feel for how close you are to a given contact, and helps you guestimate as to wether you may be detected. The good news is that if you are spotted, the game will alert you. This means is probably time to get out of dodge, as arty/missiles/bullets are on the way.