I have seen many posts where people report that the altitude showing on the DJI App on their phones is incorrect. I too have this very problem in that my Phantom 2+ reports a negative altitude when the copter is on the ground. Some suggest that the answer is to power off/on the bird so that it is acclimatized temperature wise but that doesn't seem to work for me. I was wondering why the altitude is not being provided by the GPS? Location and altitude are 2 of the main factors provided by GPS and since the copter is in contact with 6 or more satellites (you only need 4 for altitude) why is that information not being fed back to the the DJI App? Seems strange to me that since 4 satellites will give you fairly accurate altitude info then 6 or more should just about pinpoint it for you? Thanks for any feedback!