Details about assisted GPS

Discussion in 'iPhone' started by Snoopy67, Aug 13, 2009.

  1. Snoopy67 macrumors member

    Joined:
    Sep 14, 2008
    #1
    Could somebody point me to some documents that explain in detail exactly how this "assisted GPS" on the iPhone is working?

    Best regards,
    Gabriel.
     
  2. Macjames macrumors 6502a

    Joined:
    Dec 12, 2007
    Location:
    Yorkshire, England
    #2
  3. Snoopy67 thread starter macrumors member

    Joined:
    Sep 14, 2008
    #3
    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.
     
  4. aristobrat macrumors G5

    Joined:
    Oct 14, 2005
    #4
    It depends on the application, but generally speaking, the Internet is used to download map data.

    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:
    http://forums.macrumors.com/showthread.php?t=738037
     
  5. Snoopy67 thread starter macrumors member

    Joined:
    Sep 14, 2008
    #5
    So, I suppose GeoQuick.app's complaints when there is no internet available are unjustified?
    (GeoQuick just displays the coordinates.)
     
  6. aristobrat macrumors G5

    Joined:
    Oct 14, 2005
    #6
    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.
     
  7. kdarling macrumors demi-god

    kdarling

    Joined:
    Jun 9, 2007
    Location:
    First university coding class = 47 years ago
    #7
    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.
     
  8. richardhunt macrumors regular

    Joined:
    Oct 2, 2007
    #8
    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.
     

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