Re: Multiple TPV lines per sec?

[Tor Rune Skoglund]

Thank Gary,

Den 08.06.2021 20:07, skrev Gary E. Miller:
> On Tue, 8 Jun 2021 19:47:51 +0200
> Tor Rune Skoglund <trs@fourc.eu> wrote:
>
> > > This is because of your receiver firmware changing its output due to
> > > changing conditions.  Nothing can be done about it.  All GNSS
> > > receivers do it.
> > OK. I am just wondering why restarting gpsd, even in read only mode,
> > changes that output and what that condition then might be...?
> gpsd did not change anything, your receiver changed something.
>
> The receiver sends stuff to gpsd, and gpsd forwards it.  What your
> receiver sends, and when, can vary like the weather.  Garbage in,
> garbage out (GIGO).
>
> The way to see this is to capture your receivers's raw output this way:
> gpspipe -|R > raw.log
>
> Then look at it and you can start to guess why gpsd forwaards what it
> does, when it does.

By using your hint about raw output we think we figured out what is 
happening.

- The GNSS device emits both GPRMC and GNGNS messages. As long as we 
delay the startup of gpsd, gpds will only use GPRMC to report positions.

- When the vehicle enters the tunnel, GPRMC goes empty, and then gpsd 
starts emitting TPV messages based on GNGNS.

- When the vehicle leaves the tunnel, GPRMC comes back and gpsd starts 
reporting TPV based on them, in addition to GNGNS. So then we have two 
TPVs per sec.

I am not sure if this is a bug, a feature, or "just the way things are", 
but at least we now believe we know the cause. :)

$ sudo /etc/init.d/gpsd restart
 * Stopping gpsd ... [ ok ]
 * Starting gpsd ...
$ gpspipe -wR | grep "TPV\|GPRMC\|GNS"
...
$GNGNS,100353.0,6326.657403,N,01052.572860,E,AN,09,0.9,10.1,40.0,,*5D
$GPRMC,100353.0,A,6326.657403,N,01052.572860,E,45.8,251.0,090621,0.0,E,A*38
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-09T10:03:53.000Z","ept":0.005,"lat":63.444290050,"lon":10.876214333,"altHAE":50.100,"altMSL":10.100,"alt":10.100,"epx":8.343,"epy":16.521,"epv":20.700,"track":251.0000,"magtrack":251.0000,"magvar":3.9,"speed":23.562,"climb":0.800,"epd":68.7520,"eps":33.04,"epc":41.40,"geoidSep":40.000,"eph":17.100,"sep":24.700}
$GNGNS,100354.0,6326.652300,N,01052.546356,E,AN,09,0.9,9.8,40.0,,*63
$GPRMC,100354.0,A,6326.652300,N,01052.546356,E,46.1,248.5,090621,0.0,E,A*30
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-09T10:03:54.000Z","ept":0.005,"lat":63.444205000,"lon":10.875772600,"altHAE":49.800,"altMSL":9.800,"alt":9.800,"epx":8.343,"epy":16.521,"epv":20.700,"track":248.5000,"magtrack":248.5000,"magvar":3.9,"speed":23.716,"climb":-0.300,"epd":69.0949,"eps":33.04,"epc":41.40,"geoidSep":40.000,"eph":17.100,"sep":24.700}
...

Entering tunnel:

$GNGNS,100356.0,6326.642443,N,01052.495137,E,AN,09,0.9,10.0,40.0,,*5A
$GPRMC,100356.0,A,6326.642443,N,01052.495137,E,45.4,247.5,090621,0.0,E,A*30
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-09T10:03:56.000Z","ept":0.005,"lat":63.444040717,"lon":10.874918950,"altHAE":50.000,"altMSL":10.000,"alt":10.000,"epx":8.343,"epy":16.521,"epv":20.700,"track":247.5000,"magtrack":247.5000,"magvar":3.9,"speed":23.356,"climb":0.000,"epd":71.0178,"eps":33.04,"epc":41.40,"geoidSep":40.000,"eph":17.100,"sep":24.700}
$GNGNS,100357.0,,,,,NN,,,,,,*4D
$GPRMC,,V,,,,,,,,,,N*53
$GNGNS,100358.0,,,,,NN,,,,,,*42
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":1,"time":"2021-06-09T10:03:58.000Z","ept":0.005}
$GPRMC,,V,,,,,,,,,,N*53
$GNGNS,100359.0,,,,,NN,,,,,,*43
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":1,"time":"2021-06-09T10:03:59.000Z","ept":0.005}

Leaving tunnel:

GPRMC,,V,,,,,,,,,,N*53
$GNGNS,100643.0,,,,,NN,,,,,,*4D
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":1,"time":"2021-06-09T10:06:43.000Z","ept":0.005}
$GPRMC,,V,,,,,,,,,,N*53
$GNGNS,100644.0,6324.983113,N,01049.595707,E,AA,10,0.9,22.6,40.0,,*52
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-09T10:06:44.000Z","ept":0.005,"lat":63.416385217,"lon":10.826595117,"altHAE":62.600,"altMSL":22.600,"alt":22.600,"epv":20.700,"magvar":3.9,"geoidSep":40.000,"eph":17.100,"sep":24.700}
$GPRMC,100644.0,A,6324.983113,N,01049.595707,E,46.0,210.5,090621,0.0,E,A*3D
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-09T10:06:44.000Z","ept":0.005,"lat":63.416385217,"lon":10.826595117,"altHAE":62.600,"altMSL":22.600,"alt":22.600,"epv":20.700,"track":210.5000,"magtrack":210.5000,"magvar":3.9,"speed":23.664,"geoidSep":40.000,"eph":17.100,"sep":24.700}
$GNGNS,100645.0,6324.972448,N,01049.583141,E,AA,11,0.8,27.4,40.0,,*52
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-09T10:06:45.000Z","ept":0.005,"lat":63.416207467,"lon":10.826385683,"altHAE":67.400,"altMSL":27.400,"alt":27.400,"epx":8.177,"epy":9.809,"epv":18.400,"magvar":3.9,"speed":22.406,"climb":4.800,"epd":47.2859,"eps":19.62,"epc":39.10,"geoidSep":40.000,"eph":15.200,"sep":22.800}


BR,

Tor Rune Skoglund