Re: Multiple TPV lines per sec?

[Tor Rune Skoglund]

Hi Gary and List!

Thanks Gary, for the hints below. We tried using -b, -p and both but to 
no avail, so we ended up with delaying starting gpsd until we are sure 
that the modem setup has stablized.

However, we just recently noticed that the issue also appear after 
having driven through a tunnel:

After startup, a TPV comes every second as expected, for example like this:

{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-02T12:45:45.000Z","ept":0.005,"lat":63.423199333,"lon":10.581016017,"altHAE":154.000,"altMSL":113.000,"alt":113.000,"epx":8.346,"epy":8.395,"epv":18.400,"track":102.0000,"magtrack":102.0000,"magvar":3.7,"speed":19.703,"climb":0.800,"epd":45.8705,"eps":16.79,"epc":36.80,"geoidSep":41.000,"eph":13.300,"sep":20.900}
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-02T12:45:46.000Z","ept":0.005,"lat":63.423167817,"lon":10.581407800,"altHAE":154.600,"altMSL":113.600,"alt":113.600,"epx":8.346,"epy":8.395,"epv":18.400,"track":100.4000,"magtrack":100.4000,"magvar":3.7,"speed":19.549,"climb":0.600,"epd":45.7906,"eps":16.79,"epc":36.80,"geoidSep":41.000,"eph":13.300,"sep":20.900}

Then, the vehicle enters a tunnel, TPV messages comes like this once a 
second while in the tunnel (as expected):

{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":1,"time":"2021-06-02T12:47:15.000Z","ept":0.005}
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":1,"time":"2021-06-02T12:47:16.000Z","ept":0.005}

Then the vehicle leaves the tunnel; two TPVs start coming every second 
quite, e.g. like this:

{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-02T12:47:17.000Z","ept":0.005,"lat":63.421822417,"lon":10.616504367,"altHAE":143.100,"altMSL":102.100,"alt":102.100,"epv":18.400,"magvar":3.8,"geoidSep":41.000,"eph":15.200,"sep":20.900}
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-02T12:47:17.000Z","ept":0.005,"lat":63.421822417,"lon":10.616504367,"altHAE":143.100,"altMSL":102.100,"alt":102.100,"epv":18.400,"track":84.2000,"magtrack":84.2000,"magvar":3.8,"speed":21.041,"geoidSep":41.000,"eph":15.200,"sep":20.900}
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-02T12:47:18.000Z","ept":0.005,"lat":63.421827017,"lon":10.616952567,"altHAE":143.800,"altMSL":102.800,"alt":102.800,"epx":8.872,"epy":7.328,"epv":18.400,"magvar":3.8,"speed":22.389,"climb":0.700,"epd":43.2353,"eps":17.74,"epc":36.80,"geoidSep":41.000,"eph":11.400,"sep":20.900}
{"class":"TPV","device":"/dev/gpsUSB.1.6","mode":3,"time":"2021-06-02T12:47:18.000Z","ept":0.005,"lat":63.421827017,"lon":10.616952567,"altHAE":143.800,"altMSL":102.800,"alt":102.800,"epx":8.872,"epy":7.328,"epv":18.400,"track":83.8000,"magtrack":83.8000,"magvar":3.8,"speed":21.092,"climb":0.700,"epd":43.2353,"eps":17.74,"epc":36.80,"geoidSep":41.000,"eph":11.400,"sep":20.900}

As one can see, the messages that come simultaneous are quite equal, but 
"track" and "magtrack" are missing in the first one. Restarting gpsd 
resets the TPV reporting back to the initial one with one line every second.

I was thinking there might be a config option for the GNSS device or 
something that could cause this, but have no immediate clues so any help 
and pointers would be appreciated.

The GNSS in question is the one on a Sierra Wireless MC7304 modem but we 
also see on e.g. SimCom modems' GNSS.

BR,
Tor Rune Skoglund

Den 29.01.2021 18:57, skrev Gary E. Miller:

> Yo Tor!
>
> On Fri, 29 Jan 2021 13:05:39 +0100
> Tor Rune Skoglund <trs@fourc.eu> wrote:
>
> > Sometimes, we get multiple TPV lines per seconds from gpsd, e.g.
> > using gpspipe.
> Yeah multiple TPV per cycle is common and expected.  As your NMEA
> dribbles info to gpsd, gpsd can only dribble it to the client.
>
> Solutions are to run your GNSS receiver in binary mode, or optimize
> your NMEA.
>
> > After restarting gpsd, one of the lines go away.
> When gpsd starts, absent the -b or -p options, it tries to reconfigure
> your receiver for better performance.
>
> > We done some tests, but have not reached a good conclusion yet apart
> > from it helps if we delay starting/restarting gpsd too soon during
> > boot or after a new GNSS device has been added to the system.
> Fast restart interrupts the gpsd autodetection and reconfiguration.
>
> > Any quick, initial pointers and ideas on under which circumstances
> > gpsd => gpspipe would report more than one TPV message per sec would
> > be appreciated.
> Without knowing your receiver model, or how it is configured, hard to
> give any guidance.
>
> RGDS
> GARY
> ---------------------------------------------------------------------------
> Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
>         gem@rellim.com  Tel:+1 541 382 8588
>
>             Veritas liberabit vos. -- Quid est veritas?
>      "If you can't measure it, you can't improve it." - Lord Kelvin