GPS altitude is notoriously bad via consumer devices. It's better to store altitude as less than 2 bytes with the range from being a few km below sea level to t

GPS altitude is notoriously bad via consumer devices. It's better to store altitude as less than 2 bytes with the range from being a few km below sea level to the maximum altitude consumer devices will report (3,000 km -- though maybe less because there is also a speed limit at which they will stop reporting too so you can't just buy a GPS device and build a guided missile).