Re: $GPGGA / increased number of satellites

[Hans Mayer]

Yo Gary !

On 13.05.24 22:05, Gary E. Miller wrote:
> > > The sat data is not just in GPGGA, and you might be getting some
> > > binary messages as well.
> As I expected, your receiver is sending binary, not NMEA,
> That is why the gpspipe --nmea is misleading.  The GPGGA is psuedo.
I understand.
> > > > Now I realized that the logs before the upgrade had 86400 lines +/-
> > > > 1. This is one line per second. Now the files have about 10800
> > > > lines. Each night I do a logrotate.
> > > One line a seconds???  No way that is enough!
> > Big sorry, my mistake. Before the update there are 86400 lines per
> > day, but after the update I see now 108000 lines per day ( I missed a
> > zero previously )
> My comment still stands: 86400 lines per day of sat data is WAY too
> lettle.
>
> Exactly how are you "counting lines per day"??
>
> I'm totally lost.

I run this script:

gpspipe --nmea -u | grep --line-buffered GPGGA >> /var/log/gpsd/nmea.log &

This writes, as you know, one line per second. At least before the 
update at May 5th with the old version.

At midnight my logrotate daemon stops gpspipe, rotates the log files and 
start gpspipe again.

So I can easily count the lines with "wc -l" for each day. And there was 
with the old version ( from around December ) 86400 lines per day.

But now I count 108000 lines. Exactly 21600 lines more each day.

I figured out that sometimes the HDOP  column is empty and if this 
happens then there are 2 lines in one second. But this doesn't happen so 
often. Just now I see that there are two lines per second with a 
different longitude, like this

2024-05-16 22:00:24.042232: 
$GPGGA,220023.00,4808.9574000,N,01617.0305920,E,2,71,0.47,243.79,M,43.919,M,,*61
2024-05-16 22:00:24.640521: 
$GPGGA,220024.00,4808.9574060,N,01617.0305860,E,2,72,0.47,243.78,M,43.919,M,,*67

But it's interesting that it happens exactly 21600 times per day.


> > > > > By signal, I mean: L1, L2, L5, B2, etc.
> > > > >
> > > > > You can see this using cgps, or xgps.
> > > > >      
> > > > Hmm ? Not sure what you mean. When I start xgps I don't see the
> > > > bands.
> > > Yes, you do, but not obvious.  Hover your mouse over a sat icon in
> > > the skyview.
> > Yes, when I move the mouse over a sat I see a lot of additional
> > information. But what is the interesting value ?
> Well, all of it, but in this case, most important is the signal: L1, L2,
> etc.
>
> Now if you look at the sat list, to the right of the "svid" column, is the
> "sig" column.
>
> > Do you mean the SIGID. Some of the satellites have one SIGID, same
> > have 2 values.
> Yes.  Those are counted, at least in some NMEA versions, as two
> satellites, not one satellite with two signals.


OK, fine.


> The way SNMP count satellites is yet again a different way than NMEA,
> UBX, etc.  If you want to retain your sanity, stay away from SNMP.

I took the example from the man page. Fine for me not to do so.

BTW speaking about "man gpssnmp": The example "Dump the entire "sky" OID 
this way:" works for me.

The snmpget with OID skynSat.1 doesn't work. It only works with 
GPSD-MIB::skynSat.1

And the snmpwalk example with OID gpsd doesn't work too:

mayer# snmpwalk -c mysecret -v 2c localhost gpsd
gpsd: Unknown Object Identifier (Sub-id not found: (top) -> gpsd)

And the comment

# configure pass-thur of GPSD-MIB to gpssnmp

shouldn't it be

# configure pass-through of GPSD-MIB to gpssnmp

A typo ?


Kind regards

Hans


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