Re: Erratic GPS

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.
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