Anything without a global reference is dead reckoning. Optical flow sensors just give you a rotational velocity relative to ground. They don't globally locate y

Anything without a global reference is dead reckoning. Optical flow sensors just give you a rotational velocity relative to ground. They don't globally locate you. If you combine it with an altitude sensor it gives the same as an odometer would in a car, or the number of steps you take while hiking.