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From: Kyonshi <gmkeros@gmail.com>
Newsgroups: comp.mobile.android
Subject: Re: Erratic GPS
Date: Mon, 24 Jun 2024 13:45:58 +0200
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On 6/24/2024 2:24 AM, Ralph Fox wrote:
> On Sun, 23 Jun 2024 13:59:56 -0700, The Real Bev wrote:
>> On 6/23/24 1:21 PM, Andy Burns wrote:
>>> The Real Bev wrote:
>>>
>>>> Every once in a while her location will shift by as much as half a mile
>>>> and then shift back within minutes.  Is there any possible cause for this
>>>
>>> Losing view of the satellites and falling back to cell tower or wifi
>>> location?
>>
>> Standing still.  This isn't a quiz, I really want to know.
> 
> 
> GPS location relies on signals from GPS satellites being direct *line
> of sight*, and comparing the timing of signals from multiple GPS
> satellites to extremely fine accuracy (a nanosecond, the time it takes
> a signal to travel one foot).  It is not "Harry Potter" magic.  If any
> GPS satellite signal is not line of sight, this will throw the
> calculation out.
> 
> 
> If your daughter is anywhere where her device could be using a GPS
> satellite signal that is reflected off a building, wall, cliff,
> or otherwise not direct line of sight, then this is not surprising.
> 
> If your daughter is anywhere where her device does not get direct
> *line of sight* signals from at least 4 (four) GPS satellites, then
> this is also not surprising.
> 
> If your daughter was outdoors in a wide open plain, not under a roof,
> not next to a building, cliff, or wall higher than her device, not in
> a canyon, no tall buildings, hills, or mountains nearby, then and only
> then I would guess an issue on one of the GPS satellites.  Such issues
> are generally notified; see
> <https://en.wikipedia.org/wiki/Notice_Advisory_to_Navstar_Users>.
> 
> GPS was originally designed for nuclear submarines in the middle of
> the ocean, where GPS signals will always be line of sight and
> at least 4 (four) GPS satellites will always be in line of sight.
> 
> 
> This *is* a pot-luck quiz when we do not know what kind of place your
> daughter is in.
> 
> Although your daughter may be standing still, the GPS satellites are
> not.  GPS satellites are NOT geostationary.  GPS satellite signals
> do move.
> 
> 

I also noticed that Google's quality of their GPS data seems to have 
gone down lately. I started doing longer extended walks about two years 
ago, and noticed that over time the timeline Google provides has become 
somewhat unreliable in tracking how much I walked. It was better before, 
getting at least a rough estimate of the distance I walked through the 
city. The last few months it has stopped being reliable, with large 
sections of my walk missing.
This doesn't seem to be a GPS issue, as using 3rd party GPS apps 
provides much better tracking where I am.


-- 
@kyonshi@dice.camp · gmkeros.wordpress.com · @kyonshi@pixelfed.de