Here's an idea. You've just beamed down to a new planet and planted a flag. Before you go off exploring you drop a GPS marker at your beam in point - it registers your position as 0, 0. The marker sticks in the ground and flashes. Off you go exploring the underground and you find an interesting lab or some other construction. Whip out your GPS device and make a note of the coordinates it has in the HUD display - it shows your horizontal and vertical position relative to the flag marker. You can share that with other players who set their GPS device to your flag marker and then go looking for your marker underground. Even better, once you've found an interesting location drop another marker and give it a name, "underground lab" for example. When you come back to this planet later you get out your GPS device and choose a maker, by the name you gave it, from a list of markers only present on this planet. Once the waypoint is set not only will it display your current coords but the coords of the location you set so you can easily find your way back to that underground lab. It'll also beep faster the closer you get to your destination. Sharing your markers with other players would open up exciting treasure hunt situations or even traps! And in single player it's a great way to keep a log of the planets and locations you've found - making finding those places again much easier.
