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Re: Multiple TPV lines per sec?
From: |
Gary E. Miller |
Subject: |
Re: Multiple TPV lines per sec? |
Date: |
Tue, 8 Jun 2021 10:12:00 -0700 |
Yo Tor!
On Tue, 8 Jun 2021 16:19:37 +0200
Tor Rune Skoglund <trs@fourc.eu> wrote:
> 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.
Ouch. But not unexpected with a GNSS modem.
> However, we just recently noticed that the issue also appear after
> having driven through a tunnel:
Without IMU support, tunnels, and urban canyons, are problems.
> After startup, a TPV comes every second as expected, for example like
> this:
Maybe you expected that, but often not the case.
> Then, the vehicle enters a tunnel, TPV messages comes like this once
> a second while in the tunnel (as expected):
Maybe you expected that, but often not the case.
> Then the vehicle leaves the tunnel; two TPVs start coming every
> second quite, e.g. like this:
Pretty common. Note that the 2nd one contained more information than
the first one. As the data dribbles in to gpsd, gpsd pused it out as JSON.
> As one can see, the messages that come simultaneous are quite equal,
> but "track" and "magtrack" are missing in the first one.
Can 't be equal when they are different.
> Restarting
> gpsd resets the TPV reporting back to the initial one with one line
> every second.
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.
> 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.
u-blox 9 has over a thousand distinct configuration options. Feel
free to spend your next year, or two, exploring how they all interact.
Or, live with it. It is perfectly normal and expected.
> The GNSS in question is the one on a Sierra Wireless MC7304 modem but
> we also see on e.g. SimCom modems' GNSS.
Sadly, they doc is not acvailable for public download. I do see a
copyright date of 2015, and that it is EOL, so not a modern modem.
Without doc I can't say anything about your device.
RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com Tel:+1 541 382 8588
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"If you can't measure it, you can't improve it." - Lord Kelvin
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