Re: Erratic GPS

On 6/23/24 5:24 PM, 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>.

I would assume that such issues are uncommon.  Am I wrong?

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.

Lots of places, many of which do not have wifi capability -- like the Atlantic Ocean.  BUT the most surprising is when she's in a bus on an interstate highway.
Same thing when I'm being tracked (hubby, google maps, location sharing) in my car on an flat interstate.  Sudden 30-mile jump.
In my case, the ski tracks (same app) I recorded at the same ski area were vastly different with the cheesy BLU phone (sudden straight 1-mile foray into the middle of a lake, for instance) and my Motorolas and Pixel 2, which may have been off by yards.
This is clearly a phone-quality thing, but I would assume that an iPhone wouldn't have the same defects.

Although your daughter may be standing still, the GPS satellites are
not.  GPS satellites are NOT geostationary.  GPS satellite signals
do move.

--
Cheers, Bev
    If you are going to try cross-country skiing,
    start with a small country.