MrWizard wrote:
GPS...is a satellite location service
The satellite only provides location data
Altitude info or map info must be supplied by a program containing such info
Location is determine by timing responder signals and the the time in milliseconds with the identified Sat ID and matching that against a numeric tablet
That location data is a 3 dimensional location on a sphere. The three dimensions calculated include lat/ long and altitude, though it takes four satellites to provide reasonable accurate altitude data.
That wasn't an initial goal when the US Navy developed GPS, but became a base requirement when the Marines, and eventually Army adopted GPS.
GPS units time in nanoseconds - with 14 nanoseconds accuracy possible, but most devices which can receive GPS signals are only accurate to 100 nanoseconds.
That said - I'm not sure that many cell phones have GPS satellite reception capability.
I know my iPhone 5S seems unable to display an accurate position from GPS signals when I am out of the AT&T or Verizon service areas. That might be a limitation of the Google Maps app or the Apple Maps app.
Cell networks and most apps provide a good precision through ground triangulation than GPS satellites. It has become very common to describe any location service as GPS.
