GPS on iphone

737800

Good evening folks,
I was wondering does the GPS in the iPhone use 3g data?
If i am using a running app does it use 3g for the GPS positioning? if it does thats not a problem here because I'm on a plan and it doesn't cost anything extra from what I'm already paying...... the problem is that i spend a lot of time working abroad and never turn on data roaming for obvious reasons.
So the question i guess is, can i use the app abroad without costing myself a fortune???

Thanks in advance.

coylemj

It uses A-GPS which is Assisted GPS meaning it downloads (over the 3G networK) a bunch of data about the current position of the satellites which would normally take up to 12.5 minutes to download from the satellites themselves so you get a quicker fix on your location than if you relied only on satellite data.

So when you activate GPS on the iPhone it will on a once-off basis download a small amount of data over 3G but the vast bulk of the positioning data comes from the satellites and doesn't involve 3G data transfer.

http://en.wikipedia.org/wiki/Assisted_GPS

Mellor

the short answer is yes it does use some 3G data.
If you don't want to pay for this when abroad then you should turn off data-roaming

737800

Thanks for the reply Coylemj interesting stuff,
So does that mean before you leave the house if you activate an app using GPS it downloads all the satellite data via wifi does that suffice with the satellites alone providing the rest of the data while out and about without data roaming or does it need bursts of 3g data to keep the satellite data updated?

biko

It depends, some GPS apps will keep downloading maps as you drive.
Some others will not as they load the whole country into the phone when you install app.

A-GPS is only used to find your location faster/better. If you turn that off the phone will still find where it's at, just not as quick.

What app are you using?

737800

Get running... so it wouldn't be a huge amount of time or distance away from the original download of the information from the satellites.

I don't use it for traveling long distances or in the car when I'm away.

AntiVirus

A-GPS won't cost you anything on the iPhone, it uses your Wifi/Cell towers to assist in locating your position for a faster GPS lock.

737800

So bottom line is GPS apps can run while abroad without using data roaming...

Thanks for your replies guys much appreciated.

Creamy Goodness

well yes and no.

doesn't use data to get a position lock, but to download the map tiles it does, (well in the stock maps app).

AntiVirus

737800 wrote: »

So bottom line is GPS apps can run while abroad without using data roaming...

Thanks for your replies guys much appreciated.

Yes, you would just upload the data when you get to a pub with free wifi. Thats what I do anyway

Sad Professor

AntiVirus wrote: »

A-GPS won't cost you anything on the iPhone, it uses your Wifi/Cell towers to assist in locating your position for a faster GPS lock.

Yeah but the location of WiFi access points and cell towers is stored on Apple's crowd-sourced database which it needs internet access to in order to check.

I assume, however, if data roaming is disabled the phone will just be forced to use the satellite location data, but this means finding your location will take longer.

coylemj

AntiVirus wrote: »

A-GPS won't cost you anything on the iPhone, it uses your Wifi/Cell towers to assist in locating your position for a faster GPS lock.

Not corrrect, Wi-Fi/Cell Tower triangulation and GPS position fix are two completely separate processes.

The Wi-Fi/Cell Tower triangulation exercise allows the iPhone to quickly get an approximate estimate of your location. The GPS fix is much more accurate and effectively tells the device and it's apps where you are to an accuracy of a few metres.

In order to speed up the GPS positioning, the device downloads A-GPS data over the network, this is a completely separate exercise from Wi-Fi/Cell Tower triangulation and does involve data transfer.

A-GPS is data which tells the iPhone the current position of all of the GPS satellites, this data cannot be obtained from local Wi-Fi nodes, it comes via data transfer from the local cellular network so does involve data transfer.

If the iPhone did a GPS fix within the past four hours or so, it will do a hot start next time and usually wouldn't need any fresh A-GPS data.