Quote:
Originally Posted by HarryT
I was under the impression that the type of GPS used by the iPhone worked by triangulating your position from the signal strength of different local telephone "cells". I don't believe (and please correct me if I'm wrong) it involves GPS satellites at all.
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Yes and no. The original iPhone and the iPad Wifi completely rely on Wifi triangulation (Skyhook) to locate their positions, due to the lack of a GPS receiver. The iPhone 3G and it's successors, as well as the iPad Wifi + 3G, however, use A-GPS when available. When not available, they fall back transparently to Wifi triangulation. I’m not sure if they use cell towers, too. A-GPS stands for Assisted GPS and is superior to normal GPS because it boots up faster (it uses Wifi for an approximation while GPS is still calculating). A-GPS is standard on smart phones but not on dedicated navigation systems.
By the way, iOS4 introduces a new Wifi database maintained by Apple that replaces the popular Skyhook database used before. These databases store the actual information about the location of private Wifi networks. I have never actually seen a Skyhook van with big antennas on it in front of my house, so to me it’s just as magical as GPS. You kinda know how it works, but you can't believe
that it works!
Apple seems to gather this information through iPhone software, though.