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User profile for user: Case
Case Author
User level: 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/Lon 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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User profile for user: neuroanatomist
neuroanatomist
User level: Level 8
48,987 points

Posted on Nov 7, 2008 9:34 AM

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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User profile for user: neuroanatomist
neuroanatomist
User level: Level 8
48,987 points

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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User profile for user: Allan Sampson
Allan Sampson
User level: Level 10
123,677 points

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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Does the iPhone GPS function with no cellular coverage?

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