Re: different localisations for the same timestamp

[Gary E. Miller]

Yo Marcin!

On Thu, 14 Oct 2021 09:24:53 +0200
Marcin Bułka <marcin.bulka@jrdltd.co.uk> wrote:

> I am using gpsd 3.20 and I see that for almost every tpv object there
> is another tpv object with the same timestamp but with different
> localisation and I don't know how to interpret it, because a gps
> receiver can't be in two different places at one time. For example I
> have tpv objects with values like this:
> 
> timestamp: 1633008508200, eps: 0.16, lat: 45.11, lon: -0.85
> timestamp: 1633008508200, eps: 0.16, lat: 45.12, lon: -0.86
> timestamp: 1633008508300, eps: 0.15, lat: 45.12, lon: -0.86
> timestamp: 1633008508300, eps: 0.15, lat: 45.13, lon: -0.87

0.01 degree of latitude is 1.11 km, So your numbers start off almost
useless.  And why show eps (estimated speed error)?

> Additionally my gps receiver has max update rate equal to 10Hz so I
> shouldn't have a difference between timestamps in two tpv objects
> smaller than 0.1 sec.

The receiver fix rate, update rate and report rate are often not the
same.  And there is often offset between them

> Can someone help me to understand this?

First you have to help your self.  Get the raw data, and look at it.

This grabs 5 seconds of raw data, while gpsd is running with a 3D fix:

$ gpspipe -R -x 5 > raw.log

You can see what gpsd does with it this way:

$ gpsdecode  < raw.log

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

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