visual odometry is a fairly common feature for earth-creations (even toy drones) operating in GPS-denied environments. We have plenty of faux-mars environments

visual odometry is a fairly common feature for earth-creations (even toy drones) operating in GPS-denied environments. We have plenty of faux-mars environments to practice these techniques on. NASA even has their own. many of the toy indoor-use drones use such techniques for attitude/altitude-hold features when under a roof.