GPS recording has become erratic/inaccurate

Discussion in 'iPad General Discussions' started by terrypin, Sep 2, 2016.

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  1. terrypin

    terrypin
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    Anyone else having problems with GPS data from iPad or iPhone please? I'm getting poor capture, inaccuracy, and - the most striking recent change - an excessive number of trackpoints. Typically one every couple of seconds. It's either iOS or the app I use, Memory Map. (Awaiting reply from them.)

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    Terry, East Grinstead, UK
     
  2. KevinJS

    KevinJS
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    I use GPS regularly on my 5S. Haven't noticed any degradation in accuracy through several iOS updates. Haven't got 9.3.5 yet but when I do, I'll let you know if I notice any effects. My iPad is way out of date (8.0.2, I think). GPS on there functioned perfectly too, although I no longer use it for getting about.
     
  3. terrypin

    terrypin
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    Thanks Kevin.

    My focus is on discovering why the iPhone/Memory-Map combination has started behaving in this way. I can filter/reduce the number in various tools I have after the initial import, such as with GPS Utility or Memory Map itself, on the desktop PC.

    I also now have Memory-Map's reply, which is essentially that they see no evidence that the cause is due to their app.

    But I will try a test with a different app, probably Pocket Earth.

    However, I am coming to the view that it's a hardware or iOS problem with the iPhone 6S+. This thread seems to show that others are having recent problems too.
    gps not working properly after iOS 9.3 update | Official Apple Support Communities

    Some background detail follows for you and any others using iPhone or iPad for GPS work. All feedback would be appreciated.

    Sample of various walks, showing the sudden increae in trackpoint recording rate:
    https://dl.dropboxusercontent.com/u/4019461/TrackpointsSummaryTable.jpg

    The GPS file (after import to PC and saved as GPX):
    https://dl.dropboxusercontent.com/u/4019461/20160826Clapton-B.gpx

    Estimates derived from various versions of that file:

    Using original 4703 trackpoints:
    Start 09:32, end 12:28, dur'n 2:55, 6.36 miles, avg. 2.2 mph, gross asc/desc 700 ft

    Reduced in Mem-Map (PC) by a factor of 8:
    Start 09:32, end 12:28, dur'n 2:55, 6.03 miles, avg. 2.1 mph, gross asc/desc 430 ft
    Google Earth elevation profile (no GPS data): gross asc/desc 383 ft

    Converting original to a 299 waypoint route in Mem-Map gave gross asc/desc 403 ft

    My best guess, for my finished walk print out:
    Start 09:32, end 12:28, dur'n 2:55, 6.2 miles, avg. 2.1 mph, gross asc/desc 400 ft
    https://dl.dropboxusercontent.com/u/4019461/20160826Clapton-B.jpg

    And finally, filtering by a user in another forum with Garmin Basecamp, set to a minimum of 100 feet between points:
    Start 09:32, end 12:28, dur'n 2:55, 5.82 miles, avg. 2.0 mph, gross asc/desc 340 ft
    (At more than 15 times fewer than the original, that edit IMO is probably getting a bit too light on trackpoints, but it's an interestingly arguable issue!)

    My conclusion so far is that the original recording for some inexplicable reason captures a greatly excessive number of trackpoints compared to earlier recordings. That results in a significantly exaggerated gross ascent/descent, based on other evidence, personal 'feel', etc. And also a smaller exaggeration in distance. But it's then unclear what reduction is necessary to get the 'most realistic' estimates of distance and ascent/descent.

    --
    Terry, East Grinstead, UK
     
  4. twerppoet

    twerppoet
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    I've no idea what's going on, but here are two things you should try if you haven't already.

    1) Reset the iPhone by holding down the power and home buttons until the Apple logo appears. It's easy to forget this quick fix, even for experienced users.

    2) Reset All Settings under Settings > General > Reset. This does not erase any content, data, or account informastion; but it does default a lot of other settings. You'll have to retweek the iPhone to get thigns back to the way you're used to using it. Do not confuse this with the "erase all contents and settings" option.

    I mention this one because sometime settings switches get stuck and or hidden during a new iOS install and subsequent restore from backup. Whether Location Services are, or even can be, messed up this way? I don't know. But it's worth a try before resorting to an Apple Store appointment for testing.
     

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