@romin The US military used to make GPS for civilian use almost useful by messing with the accuracy, but eventually other positioning technologies improved to the point that the wrong-action takers would just use other positioning systems or inertial guidance instead of GPS, so they decided to allow receivers to have reasonable accuracy.

They still require that receivers shop working at high airspeed (so you can't make a GPS guided drone, so no fun) and that's usually implemented via proprietary software it seems.