GPS question....hardware

Discussion in 'iPhone Tips, Help and Troubleshooting' started by firedogut, Sep 16, 2009.

  1. firedogut macrumors regular

    Sep 9, 2009
    So I had a very questions about the GPS on the iPhone 3GS.

    Is it the same as the iPhone 3G?
    What kind of GPS is it, are we talking real DOD satellites or the cell network?

    I've searched the forum and googled it but seem to get conflicting results.
  2. tcarcur macrumors newbie

    Jan 16, 2008
    The 3G and 3GS work with GPS satellites.

    Since it takes time figuring out which satellite is currently above you, the iPhone uses cellular triangulation to determine your overall location so it can determine which satellite is above you and give you a location faster.

    Now, this doesn't mean the GPS in the iPhone won't work without cell signal. It works, but takes longer, sometimes up to 15 minutes.

    But yes, the 3GS and 3GS use the same satellites other GPS devices.

    Hope this answers your question.
  3. firedogut thread starter macrumors regular

    Sep 9, 2009
    ok so if you buy GPS software you can use it like areas that have zero cell service?

    So the iPhone 3GS uses cell Towers, Wifi, and satellite.

    How does the GPS chip compare to the chips found in other GPS devices such as Tom Tom, Garmin, Magellan....etc
  4. yg17 macrumors G5


    Aug 1, 2004
    St. Louis, MO
  5. tcarcur macrumors newbie

    Jan 16, 2008
    yes, but if the gps software requires internet for maps, you won't have maps (ie. AT&T Navigator). the TomTom app works even with no cell signal or anything

    Yep, all three so it can get your location faster.

    I don't know at the technical level, but should work equally. Now, the 3G has no compass, which other gps devices might have. the 3GS has the compass hardware together with the gps chip
  6. scoiattolo49 macrumors newbie

    Sep 17, 2009
    Please note that Wi-Fi is NOT used in determining the position! :eek: To download data yes but never to get a position fix

    Plus most navigation applications (Tomtom, Navigon, etc) don't use at all the cell triangulation to determine your position (and at the moment they don't even use the 3GS compass). They only use on the internal GPS receiver. The one included in the 3G(S) is an assisted one.

    Assisted GPS means that your GPS receiver can use a set of data that direct it on the satellites position at that particular time. This increases the speed of the fix. These data need to be periodically updated, downloading them via a server.

    Bear in mind that you do need a clear view of the sky to get a fast satellite fix. And that without any form of connection (GPRS, Wi-Fi) your assisted gps data may not be up-to-date.
    In some circumstances you may need a long time to get a fix, especially the first one.

    Google Maps instead uses (if the GPS is not available) the network cells triangulation to get the position, but this needs network coverage and also its accuracy depends on where you are. In an area with few antennas you could be off quite a lot!
    Besides Maps needs to download the map on request (so a network coverage or WiFi.. ).
  7. firedogut thread starter macrumors regular

    Sep 9, 2009
    From the apple webiste
    Turns out the iphone uses the Skyhook Wi-Fi Positioning System (WPS). This system takes advantage of the hundreds of millions of Wi-Fi access points throughout populated areas, WPS consistently provides accurate location information indoors and in urban areas.

    Wi-FI is used in determining the position!:eek:

    you should not use bold unless you don't mind putting your foot in your mouth. :rolleyes:
  8. scoiattolo49 macrumors newbie

    Sep 17, 2009
    Skyhook Wi-Fi is a system that in theory should work (according to them) but in reality is nearly never used.

    If you look at the Skyhook they claim an extensive coverage but they always claim that this is achieved in combination with the cellular network!

    The main problem of the system is that it relies on a Wi-Fi spot location put in a database. This rules out all the private Wi-Fi networks (home, offices, etc.) and only the public ones may be used. Plus the position of the access points should not change since the last survey done by Skyhook.
    Basically the system only works in some urban areas in the States.and in a few big cities in the rest of the world.

    If you don't believe me try by yourself: switch off the GPRS reception, stay indoors so the GPS doesn't work and just enable the Wi-Fi... see if you get a position ;)
  9. firedogut thread starter macrumors regular

    Sep 9, 2009
    airplane mode on. wifi on.

    it works.....i'm off by about 50 feet. it shows me across the street when i zoom in. with my airplane mode off and wi fi off it shows me on the correct side of the street.
  10. soLoredd macrumors 6502a

    Mar 12, 2007
    Ok, wait a minute. While Skyhook is not at the level of a stand-alone GPS receiver, it works pretty damn good. It has since the 2G. Now, I'll give you the fact that it does vary in terms of precision but I'd say about 85% of the time, Wi-Fi has been able to pin-point me at my home.

    I'd also go as far as to say with my previous 2G the Wi-Fi was not nearly as strong as my 3GS. With my 3GS I am able to pick up access points in my area that I could only get on my Mac.

    Said that, if you are on the move, using the cell network is the best way (in my opinion). In comparison to my Nuvi, I can't believe how fast the 3GS is able to get a location fix even with just Google Maps. The other day I was stuck on the freeway in accident traffic. Thought I'd try Maps to see if the upcoming exit could get me around it. A matter of seconds it found me. I couldn't even get through the menus on my Nuvi in that amount of time. I'm still trying to convince myself to spend the $90 on Navigon. It looks very good.
  11. scoiattolo49 macrumors newbie

    Sep 17, 2009
    Wait a moment before jumping on me.. ;)

    When I said Wi-Fi is never used, I referred specifically to the proper navigation programs, like Tomtom, Navigon and Copilot.
    In fact as i said they don't even use (in their current release) the cells triangulation and the compass (3GS).
    Only GPS is used
  12. crwd2008 macrumors newbie

    Sep 12, 2009
    Great GPS FREE APP

    Try this GPS app, it is amazing !! It's called GPS lite....enjoy
  13. DustyLBottoms macrumors regular

    Sep 8, 2009
    Actually - the SkyHook system is very accurate - and is used quite often.

    Just ask anyone with a Touch.....

    I owned a touch for 3 months before I got my phone. And the location system though google maps always had me within 30 feet of my actual location.

  14. rainynight33 macrumors newbie

    Sep 19, 2009
    my tomtom gps app doesnt work just with location services, it works WITH wifi turned on OR my carrier's network signal turned on...

    is my gps chip defective?

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