iPhone GPS/Location Accuracy

Discussion in 'iPhone Tips, Help and Troubleshooting' started by rbwrath, Sep 26, 2008.

  1. rbwrath macrumors newbie

    Sep 26, 2008
    Not sure if this has been asked yet... did a search but didn't see anything.

    I was wondering if there's any place where I can find out the accuracy of the GPS and WiFi location finder. Or if anyone has experience with these.

    Any help would be great!

    Thanks :)
  2. marcusabe macrumors newbie

    Oct 9, 2008
    GPS Accuracy

    Same doubt here. My iPhone 3G's GPS is showing my location with an inaccuracy of 500-600 meters or more. I've looked up the internet and found out that iPhone GPS uses a mix of wi-fi, cellular towers triangulation and GPS signals (A-GPS) to find my location. So it differs from a regular GPS navigator.

    Like I live in a 90,000 pop town and my carrier has only 5 cellular towers here, the iPhone's GPS has a great inaccuracy. I'm very disappointed!
  3. Me1000 macrumors 68000


    Jul 15, 2006
    I think the GPS is pretty accurate...

    It is the maps that are off.
  4. marcusabe macrumors newbie

    Oct 9, 2008
    Do you think that can be a problem with google maps?
  5. ChrisA macrumors G4

    Jan 5, 2006
    Redondo Beach, California
    This is very likely the case in many parts of the world. If you have ever sailed on the ocean then you know the saying "A GPS can get you close, but radar will get you there." Many of the maps we use were last surveyed in the 1950's

    The other common source of error is "user error". You may have crossed up a couple of ellipsoids. The Earth is not spherical. Map makers assume an approximate ellipsoidal shape that is a better fit to the real Earth than a sphere. But the exact ellipsoidal shape used can vary. To compare latitude and longitude between the GPS and a map both must use the same exact ellipsoidal shape. "WGS84" is the most common ellipsoid but it is not universal.

    OK a shorter way to say the above is that "all maps and GPSes do not use the same latitude and longitude system. If the GPS and the map are on different systems you will see an error.

    One other thing to remember is that the iPhone will fall back to using cell toweres if it can't get a GPS signal. Just about anything can block a GPS. The GPS needs a clear view of the sky not blocked by trees or buildings.
  6. marcusabe macrumors newbie

    Oct 9, 2008
    Thanks ChrisA. Maybe you're right because I was outdoors away from buildings and trees when trying "locate me" on Google Maps. And had already reseted networking settings.
  7. raybrownjr macrumors newbie

    Dec 8, 2008
    Iphone Gps Accuracy

    Apparently The Iphone Uses Cell Tower Triangulation If It Is Unable To Get A Good 3d Fix With Three Or More Sats. If You're Among Or In Buildings, That's A Good Deal Because Multipath Inaccuracies Are Rampant There. The Best Thing To Do Is To Go To A Ball Field And Stand On The Pitchers Mound Or In The Center Circle Of A Soccer Field Using The View In Google Maps To Determine Accuracy. Do This At Different Times Day And Night. You Should Get Within 1o Meters Or 33 Feet 95% Of The Time If No Multipath Problems. Iphone Is Just As Good As Any Recreational Grade Gps. I Don't Know If The Cell Tower(s) Provide Differential Corrections And Send Them To Iphone. You Should Then Get Submeter Accuracy. That Might Be Suggested To Att. Thanks-ray Brown-seattle.
  8. cjm3113 macrumors 6502

    Nov 30, 2008
    Strange, it must have to do with how it determines where you are because mine always puts me inside of my house when I check out the maps. I am always surprised how perfect it is.
  9. Stella macrumors G3


    Apr 21, 2003

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