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Devices marketed as "GPS" are not always full fledged GPS. I realized that fact because I purchased a tablet, and once I went out with it using the GPS, my position became unavailable or very inaccurate, very quickly. AGPS means assisted GPS. Essentially, it means that you need some kind of list of satellites, or some kind of "init" data for GPS to boot up, and I think I heard this list is streamed by satellites, but with AGPS, you won't receive this list from satellites, but from some network thing. To be honest I'm not sure 100% sure of the things I just said (I'm repeating some answer I got on stackexchange), but I can deduct that AGPS devices are not autonomous, they need a little bit of networking in order to calculate an accurate position. Although there are many real GPS devices out there, I'm almost certain my new smartphone is full GPS because I have no SIM and no data plan and it guided me for a 50km trip, but I don't know what are the capabilities of other devices. To be really honest, intelligence agencies might have pushed for such and such throttled GPS featured chip, that forces those to use networking, again, for allowing a third party to track the position and avoid autonomous positioning. It would be a conspiracy theory at this point, but by listening to Snowden, it would make sense. |