Details about assisted GPS

[Snoopy67]

Could somebody point me to some documents that explain in detail exactly how this "assisted GPS" on the iPhone is working?

Best regards,
Gabriel.

 

[Macjames]

Basically the iPhone assisted GPS works like a normal GPS but to speed up the triangulation it uses the mobile phone towers as well to locate itself.

http://arstechnica.com/apple/news/2008/06/assisted-gps-and-the-iphone.ars

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

http://www.everyipod.com/iphone-faq...d-gps-how-gps-works-real-time-navigation.html

That should give you a good understand of what the iPhone is doing

 

[Snoopy67]

Thanks a lot.

It still not quite clear to me, exactly what data are transmitted via Internet: is it just the almanac? or more?

And is the iPhone capable of doing full GPS, if there is no internet available?
(the it would be, of course, much slower at getting a fix.)

Regards,
Gabriel.

 

[aristobrat]

It still not quite clear to me, exactly what data are transmitted via Internet: is it just the almanac? or more?

It depends on the application, but generally speaking, the Internet is used to download map data.

And is the iPhone capable of doing full GPS, if there is no internet available?

The iPhone is able to figure out its GPS coordinates without an Internet connection, but it's up to the application that you're using as to if the app will work properly without an Internet connection. For example, if you have an iPhone 3GS and put it into Flight Mode (so that it doesn't use data), the Compass app should show you accurate GPS coordinates.

Some of them are coded to show a "visual" of your location, and not all of them are graceful when they're unable to do that.

Here's a thread about a guy who ran into issues with an app like that:
https://forums.macrumors.com/threads/738037/

 

[Snoopy67]

It depends on the application, but generally speaking, the Internet is used to download map data.

So, I suppose GeoQuick.app's complaints when there is no internet available are unjustified?
(GeoQuick just displays the coordinates.)

 

[aristobrat]

I've never used that app before.

I have left my iPhone in Flight Mode and have had it update its GPS coordinates on the Compass app before though.

 

[kdarling]

It still not quite clear to me, exactly what data are transmitted via Internet: is it just the almanac? or more?

Assistance information usually contains the almanac/ephemeris, plus an initial location estimate based on the tower id sent in the request.

For much more info, look up:

RRLP - Radio Resource Location Services Protocol, which is the info sent over the...

SUPL - Secure User Plane Location

PS. Ignore almost every article you read about A-GPS on the iPhone. Most are full of info about the phone using wifi or tower ids. Those are simply alternative locating methods, and are not directly used or required by A-GPS.

 

[richardhunt]

The navigon app in the app store does not use internet data when used. So it will work without data and just like a Tom Tom type hand held GPS with turn by turn directions. It's great, I use it periodically when I want to find the nearest restaurant to where I am.