The Xenomorph knows where it is at all times. It knows this because it knows where it isn't, by subtracting where it is, from where it isn't, or where it isn't, from where it is, whichever is greater, it obtains a difference, or deviation. The Director AI uses deviations to generate corrective commands to send the Xenomorph from a position where it is, to a position where it isn't, and arriving at a position where it wasn't, it now is ripping your face off.