AW: Decreasing number of used satellites

[Wielant, Ulrich]

Hi Gary, hi all,

thanks a lot for your response.
Following Gregs and your comments I further investigated the case.

Gpsd version: 3.23.1 (I am using the opensuse 15.2 gpsd package)
GPS: Garmin 24xd HVS
Firmware: unknown - I cannot find any hint about the firmware version NMEA 
version: don't know - have to ask Garmin but that takes time. I guess it's < 
4.11.

I managed to configure the GPS so that only GPS satellites are used and no 
other systems like GLONASS, QZSS etc.
So all GSA and GSV messages should only report GPS PRNs.

After I start gpsd most of the time all satellites are tagged with used=false 
in the SKY sentence.
But in rare cases after I start gpsd they are tagged with used=true.

I have created gpsd debugs for both cases start gpsd with the following 
parameters: /usr/sbin/gpsd -G -n -D 5 -N /dev/ttyS0 I have compared the debugs 
but I do not find the point why gpsd behaves different.

The only difference I can find is that DOP is set in the mask when satellites 
are reported as used.
The GSA messages looks good to me. I only wonder that PRN 26 is sometimes 
reported twice. But that happens in both cases.

used=true:   gpsd:IO: <= GPS: 
$GPGSA,A,3,05,16,18,23,26,26,27,,,,,,0.90,0.55,0.72*01
used=false:  gpsd:IO: <= GPS: 
$GPGSA,A,3,05,16,18,23,26,27,,,,,,,0.90,0.55,0.72*05

With satellites used=false I see:
gpsd:IO: <= GPS: 
$GPGSV,2,1,06,05,20,046,43,16,50,298,44,18,71,111,45,23,14,144,39*7F
gpsd:PROG: NMEA0183: xPGSV: part 1 of 2, last_gsv_talker '0'  last_gsv_sigid 0
gpsd:PROG: NMEA0183: xPGSV: new part 1, last_gsv_talker '0', zeroing
gpsd:PROG: NMEA0183: xxGSV: Partial satellite data (1 of 2).
gpsd:PROG: NMEA0183: GPGSV is just after a cycle ender.
gpsd:IO: <= GPS: $GPGSV,2,2,06,26,75,244,46,27,21,268,43*74
gpsd:PROG: NMEA0183: xPGSV: part 2 of 2, last_gsv_talker '0x50'  last_gsv_sigid 0
gpsd:PROG: NMEA0183: GPGSV is just after a cycle ender.
gpsd:INFO: Sats used (0):
gpsd:PROG: Changed mask: {ONLINE|SATELLITE|PACKET} with reliable cycle detection

With satellites used=true I see:
gpsd:IO: <= GPS: 
$GPGSV,2,1,06,05,20,046,44,16,50,298,45,18,71,112,45,23,14,144,38*7B
gpsd:PROG: NMEA0183: xPGSV: part 1 of 2, last_gsv_talker '0'  last_gsv_sigid 0
gpsd:PROG: NMEA0183: xPGSV: new part 1, last_gsv_talker '0', zeroing
gpsd:PROG: NMEA0183: xxGSV: Partial satellite data (1 of 2).
gpsd:PROG: NMEA0183: GPGSV is just after a cycle ender.
gpsd:IO: <= GPS: $GPGSV,2,2,06,26,75,245,47,27,21,268,43*74
gpsd:PROG: NMEA0183: xPGSV: part 2 of 2, last_gsv_talker '0x50'  last_gsv_sigid 0
gpsd:PROG: NMEA0183: GPGSV is just after a cycle ender.
gpsd:INFO: PRN  5 az  46.0 el 20.0 ( 0.675958,  0.652765,  0.342020)
gpsd:INFO: PRN 16 az 298.0 el 50.0 (-0.567548,  0.301771,  0.766044)
gpsd:INFO: PRN 18 az 112.0 el 71.0 ( 0.301862, -0.121960,  0.945519)
gpsd:INFO: PRN 23 az 144.0 el 14.0 ( 0.570326, -0.784986,  0.241922)
gpsd:INFO: PRN 26 az 245.0 el 75.0 (-0.234570, -0.109382,  0.965926)
gpsd:INFO: PRN 27 az 268.0 el 21.0 (-0.933012, -0.032581,  0.358368)
gpsd:INFO: Sats used (6):
gpsd:PROG: Changed mask: {ONLINE|DOP|SATELLITE|PACKET} with reliable cycle 
detection


Do you see what makes the difference between gpsd reporting satellites as used 
and not as used?

Thanks for your assistance!
Ulrich

-----Ursprüngliche Nachricht-----
Von: gpsd-users <gpsd-users-bounces+u.wielant=leonardogermany.com@nongnu.org> 
Im Auftrag von Gary E. Miller
Gesendet: Montag, 13. Juni 2022 18:10
Cc: gpsd-users@nongnu.org
Betreff: Re: Decreasing number of used satellites

Yo Ulrich!

On Mon, 13 Jun 2022 12:30:38 +0000
"Wielant, Ulrich" <U.Wielant@leonardogermany.com> wrote:

> I updated to gpsd 3.23.1 (I hope 3.23.1 is current enough...) I still
> have problems with the number of used satellites.

3.24 is current.  Multiple GNSS NMEA is rapdily evolving.

>  I have attached the output of cgps and gpsmon captured at rather the
> same time.

Not helpful.  What you need to send is the NMEA you get, with that I can see 
what cgps would show.  Ignore gpsmon, it is obsolete.

> The GPGSV and GNGSA NMEA sentences describe a large number of
> satellites. The SKY JSON object in cgps indicate that none of them are
> used.

Without your NMEA, no way to see what is happening.

> Greg, can you tell me, why the gpsd indicates that none of the
> satellites are used?

Not without your NMEA.

> Please tell me if you need any other information.

Can you verify your GNSS receeiver is set to NMEA 4.11?  Earlier versions of 
NMEA did not forsee today's multiple constellations.

Your exact make, model, firmware version, and receiver settings will also be 
helpful.

RGDS
GARY
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gpsd_debug_sats_used_true.txt
Description: gpsd_debug_sats_used_true.txt

gpsd_debug_sats_used_false.txt
Description: gpsd_debug_sats_used_false.txt