On land, we have Google Maps. In the air, drones use RTK GPS. Underwater? GPS signals are blocked by water. Without expensive acoustic positioning systems (USBL), most consumer ROV pilots are flying blind. This is where the concept of comes into play.
Have you successfully implemented a map hack for your ROV using Android? Join the discussion at /r/rov or /r/diydrones. hack map rov android
Start small. Test your dead reckoning hack in a swimming pool. Draw a square. If the map shows a square, you have succeeded. If it shows a spiral, debug your filters. Once you move to open water, remember: The map is always wrong—it is just a model. Use your eyes, your tether, and your common sense. On land, we have Google Maps