Does the iPhone GPS function with no cellular coverage?

Question

Level 1

75 points

Does the iPhone GPS function with no cellular coverage?

The raging question here today is whether the GPS function will work while there is no phone coverage at all... For example, I have iNavX installed - it's a nautical charting application. All of the charts for the regions I'm traveling in are already downloaded to the iPhone, so all it really needs is a good Lat/*** GPS signal to plot position.

I know, from plenty of research, that aGPS can be opened up such that it will be visible to the end user and thus an app can access the chip/data even without the cellular network (3G or EDGE) available.

It would appear from my incidental experiences that it will, as I've had an iPhone 3G on my boat in zero cell coverage areas, and the charting app DOES plot position. (I've always wondered, however, whether or not I was picking up an incredibly weak cell signal that might be assisting??) I guess I've just answered my own question via trial and error, but can anyone shed any more "technical" light on the matter?

TIA!
-Case

MBP, 20" iMac, a couple of G4 PowerBooks and a Mini in charge of hosting., Mac OS X (10.4.10)

Posted on Nov 7, 2008 9:26 AM

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Answer 1

Nov 7, 2008 9:34 AM in response to Case

Yes, it will work. aGPS incorporates a "true" GPS receiver, and uses the assistance server (from the cellular data network) if it's available, to speed up satellite lock and to compensate if 4 satellites are not in view. But, the assistance is not required for GPS to function (assuming at least 4 satellites are in view), although it will take longer to get a position lock.

I'd also say that you do seem to have answered your question empirically, as well!

Most of the debate results from the fact that the Maps app requires a data connection (cellular or Wi-Fi) to download the map data on which to plot the location obtained from the GPS.

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Answer 2

Nov 7, 2008 9:35 AM in response to Case

The iPhone includes a GPS radio, so if you are using an application with charts or maps downloaded and available on the iPhone, you don't need cellular access.

The Maps application requires internet access to download map data for your current location. If you are using an app with charts or maps available locally on the iPhone, all you need is GPS access.

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Answer 3

Nov 9, 2008 9:57 AM in response to Case

It works but, if I did have a cellular data connection sometimes before and then modify the apn to be sure to cut all connections, the counter continue to increase. This seems to be a bug in this counter.
However, shutting down and restarting the iPhone, the counter is OK it seems. (This is on my iPhone 3G , 2.1)

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Answer 4

icebike

Level 3

740 points

Nov 7, 2008 1:12 PM in response to Case

See this thread:
http://discussions.apple.com/thread.jspa?messageID=8332707
Lots of good info in that thread. The issue is settled.

If the iPhone will work in the Gulf of Mexico, it will work in Stephens Passage.

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Answer 5

Case Author

Level 1

75 points

Nov 7, 2008 8:20 PM in response to icebike

icebike wrote:
If the iPhone will work in the Gulf of Mexico, it will work in Stephens Passage.

Actually, Chatham, Icy and Peril Straits and Cross Sound are more my stomping grounds, but point taken. Thanks for your help in both threads!

-Case

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