Originally Posted by
airpolice
There is no GPS (as we all know it) in an iPad or iPhone. They call it assisted gps and it is just autotriangulation from cellular network masts.
WRONG Assisted GPS (A-GPS) means that getting the initial GPS fix is sped up through use of downloaded data, rather than having to get the data directly from the satellites. It is still GPS - using the same satellites to get a position fix as all other GPS devices. Once an initial fix is established, downloaded data is not longer used.
When on the ground, you are likely to notice that getting an initial fix is much faster on devices (phones, etc) using this, especially in built up areas, than traditional GPS devices.
The issue is that some devices appear to rely heavily on A-GPS to get their initial fix. Therefore if you try to start such devices when there is no data network available, they can struggle to ever get a GPS fix (the long lag time may cause something to time out, and so will no longer look for a signal).
If no network data is available, satellite data needs downloaded from the satellites themselves, which requires maintaining a download from a single satellite for about 30-40 seconds. If a device has a poor receiver, or in a poor signal area, an initial fix will never seem to happen.
See
Assisted GPS - Wikipedia, the free encyclopedia