Inertial navigation
I would have thought a highly accurate inertial navigation system (based on accelerometers and gyroscopes), perhaps coupled with some wearable "boot sensors" to more accurately track distance and a digital compass would provide much more accurate, dependable position fixes in 3 axes essentially via dead reckoning.
Certainly distance could be very easily tracked - unlike submarines, ships and aircraft using dead reckoning, the medium (water, air etc) isn't moving due to currents, so there's less drift to account for.
Perhaps a camera sensor that works like a giant optical mouse could track distance travelled like an electronic trundle wheel...