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From: The Real Bev <bashley101@gmail.com>
Newsgroups: comp.mobile.android
Subject: Re: Erratic GPS
Date: Tue, 25 Jun 2024 08:12:45 -0700
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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:
>>>=20
>>>> Every once in a while her location will shift by as much as half a m=
ile=20
>>>> and then shift back within minutes.=C2=A0 Is there any possible caus=
e for this
>>>=20
>>> Losing view of the satellites and falling back to cell tower or wifi
>>> location?
>>=20
>> Standing still.  This isn't a quiz, I really want to know.
>=20
>=20
> 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.
>=20
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> 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=20
Atlantic Ocean.  BUT the most surprising is when she's in a bus on an=20
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=20
were vastly different with the cheesy BLU phone (sudden straight 1-mile=20
foray into the middle of a lake, for instance) and my Motorolas and=20
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.


--=20
Cheers, Bev
    If you are going to try cross-country skiing,
    start with a small country.