Re: GPS/PPM very large offset

[B&A Consultants]

Hello Garry,

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/gpsd.pid /dev/ttyAMA0

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

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

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

# Pools for Gentoo users
pool 0.fr.pool.ntp.org
pool 1.fr.pool.ntp.org
pool 2.fr.pool.ntp.org
pool 3.fr.pool.ntp.org

# These are the restrictions most people want
restrict default kod limited nomodify nopeer noquery
restrict -6 default kod limited nomodify nopeer noquery
restrict 127.0.0.1
restrict -6 ::1

# Don't change this location.
driftfile /var/lib/ntp/ntp.drift

> 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)│
│ Latitude:         somewhere N             │
│ Longitude:        somewhere E             │
│ Alt (HAE, MSL):    173.500,    125.000 m  │
│ Speed:             0.10 kph               │
│ Track (true, var):                n/a deg │
│ Climb:            -6.00 m/min             │
│ Status:         3D DGPS FIX (647 secs)    │
│ Long Err  (XDOP, EPX):  0.49, +/-  1.8 m  │
│ Lat Err   (YDOP, EPY):  0.69, +/-  2.6 m  │
│ Alt Err   (VDOP, EPV):  1.31, +/-  7.5 m  │
│ 2D Err    (HDOP, CEP):  0.85, +/-  4.0 m  │
│ 3D Err    (PDOP, SEP):  1.56, +/-  7.4 m  │
│ Time Err  (TDOP):       0.85              │
│ Geo Err   (GDOP):       1.79              │
│ ECEF X, VX:              n/a    n/a    /s │
│ ECEF Y, VY:              n/a    n/a    /s │
│ ECEF Z, VZ:              n/a    n/a    /s │
│ Speed Err (EPS):       +/- 18.7 kph       │
│ Track Err (EPD):        n/a               │
│ Time offset:            6.928768431 sec   │
│ Grid Square:            square id         │

23-24 satellites seen, 13 to 16 used (GP and GL).

Do not know if it may be useful, but the Alt (HAE, MSL) line oscillates 
betwene some values and n/a. Same thing for Track, Climb and ECF (X, Y, 
Z, VX, VY and VZ).

Regards,
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