Nearly one month ago I purchased the new iPhone 3GS. All in all I am very content with the phone and I honestly don’t know why I stayed with my WM6 phone for so long (even if I pimped it to behave like an iPhone).
Nevertheless there was one big head-scratcher that kept nibbling on my mind: If I try to locate my position via google maps there is quite a big variation between my actual position and the position Google marks as my actual position:
The green fixing pin ought to mark my actual position; stupidly my real position is where the red pin is located. The difference between the two markers is approximately 1000 ft.
After investigating a little bit I discovered where the problem is: The iPhone uses A-GPS (assisted GPS; a carrier network dependent system) to compute the actual position. This technique can be a little imprecise. The advantage of this method is the increased speed and that it works at places where a normal GPS-unit fails . To check if the variation is really caused by A-GPS I turned on the flight mode (alternatively you can switch off data roaming) and determined my positition via Wi-Fi (unfortunaltley google maps doesn’t work without an active connection). You can see the result in the picture below:
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