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Intermittent: Absurd (very inaccurate) GPS coordinates
My Samsung Galaxy SII GT-I9100 phone (Android 4.0.4) normally gives near-perfect GPS results, both with the built-in "Maps" app and with ViewRanger.
However today I noticed that ViewRanger was recording a track that included intermittent rogue coordinates. Not just going a bit off-course but with errors of about 20-30 degrees in latitude (though still with fairly good longitude). While I was driving, with the phone laid horizontally, the tracking was fine. When I got out for a walk and had the phone held horizontally or vertically in my hand or vertically in my anorak or trouser pocket, I was getting good tracking at times, with several consecutive readings having stupid latitude and elevation values. This repeated every few minutes until I got back to the car and put the phone between the seats.
I may have inadvertently have had my hand/body covering the GPS antenna (or with coins in my trouser pocket or a zip in my anorak pocket close to the antenna), but my experience with another phone (Nokia) is that you simply get missed readings, or else errors of a hundred yards or so rather than hundreds of miles!
Should GPS devices return rogue values if they get poor DOP values (eg few satellites), or should they just fail to return a value which is clearly in error? Going through the GPX track file weeding out rogue values is no fun :-)
I've seen reference to the System | Location Services | Use Sensor Aiding which can cause erratic results if it is turned on, which it was. Could this be the cause of my results or is it a red herring? I'll try recording a track tomorrow with it turned off. What about "Use Google location service" - does that carry any health warnings?
I also saw the same symptom with the "Maps" app yesterday, but I thought it was due to poor satellite visibility while I was indoors; I didn't see any errors while I was out for a walk then. Mind you, I may have missed the odd glitch because Maps doesn't record a track so if you are not watching the screen at the time you may miss it misbehaving.
Visibility of satellites should have been good - I was in wide open countryside with no steel-framed buildings or narrow ravines to limit visibility of satellites. Two other phones running ViewRanger (one the Nokia on Symbian, the other a Google Nexus on Android) recorded perfect tracks over the same walk at the same time - OK, we were testing out our various Christmas presents :-)