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Re: GPS/PPM very large offset

From: Gary E. Miller
Subject: Re: GPS/PPM very large offset
Date: Fri, 6 Nov 2020 11:45:23 -0800

Yo B&A!

On Fri, 6 Nov 2020 20:24:52 +0100
B&A Consultants <> wrote:

> Hello Garry,

One 'r'.

> On 06/11/2020 19:46, Gary E. Miller wrote:
> > We need some of you implementation details to take a guess here:
> >          gpsd version  
> gpsd 3.21


> >          gpsd command line  
> Started through openrc.
> /usr/sbin/gpsd -n -r -F /run/gpsd.sock -P /run/ /dev/ttyAMA0

Usually you do -F for hotplug.  You doing any hotplugging?  But not
really a problem.

> >          ntp.conf  
> We are using ntpsec, but we can switch to ntp if it makes things
> easier to pinpoint the problem.

You realize gpsd is also the NTPsec team?

> # GPS PPS reference (NTP1)
> refclock shm unit 1 refid PPS

Missing "prefer", but not your problem.

> # GPS Serial data reference (NTP0)
> refclock shm unit 0 refid GPS

Missing "ignore", but not your problem.

> > Does cgps show a valid 2d fix?  For how long?
> > How many leap seconds does cgps show?  
> Here is an example of cgps display.
> │ Time:        2020-11-06T19:15:58.000Z (18)│

You have the correct leap seconds; 18.

So no idea where your 5 seconds is coming from.

> │ Latitude:         somewhere N             │
> │ Longitude:      somewhere E             │

You think we don't know you are near Compiegne, Berck-Plage,
Allonne and Poissy?  About 49N, 2E.

> Do not know if it may be useful, but the Alt (HAE, MSL) line
> oscillates betwene some values and n/a.

Yup, that is what your GPS is sending to gpsd, gpsd just repeats it.
The joys of NMEA.  Depending on your receiver you can fix that.  For
u-blox go into binary mode.

What is your GPS model, and how is it configured?

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703  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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