iPhone 4 background location service question

Question

I\'m looking into the new background location service options in the iPhone 4 SDK. It allows an app to run in the background and receive location updates from the device.

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Answer 1

As Steve Jobs mentioned in the OS 4 introduction, the low power mode uses cell tower triangulation and does not activate GPS unit. Since the iPhone phone module needs to keep a connection to the cell network anyway, there should be no impact on battery life.

Since the precision of a location fix with cell tower triangulation is anywhere between a few dozen meters (in dense city locations) and a few miles, I think 30 ft is not a significant location change. I don't know the specifics, though (and as mentioned by the commenters, the Apple dev forums are the right place to talk about those).

Answer 2

I've recently done some field testing of the new background location service to get an idea of what constitutes a significant location update, what kind of accuracy to expect for the location hits and our general experiences using it.

The results are detailed in a fairly lengthy blog post:

iPhone Background GPS: Accurate to 500 meters, not enough for foot traffic