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Re: Strangeness with speed

From: Gary E. Miller
Subject: Re: Strangeness with speed
Date: Mon, 14 Feb 2022 12:41:27 -0800

Yo Владимир!

On Mon, 14 Feb 2022 23:32:01 +0300
Владимир Калачихин <> wrote:

> 14.02.2022 22:15, Gary E. Miller пишет:
> > Since the time never changed, gpsd never was asked to compute
> > speed.  gpsd uses the time steps to internally trigger state
> > changes.  
> Changed since when?

Since the last fix.

> What needs to gpsd for compute of speed?

two Time and Position Pairs.  speed = (p2 - p2) / (t2 - t1)

But no need to get deep.  Your NMEA is broken.  Your NMEA needs to look
like valid NMEA.  Otherwise it will fail in ways no one expects.

> And, the RMC sentence has speed from the GNSS receiver. The gpsd
> doesn't use it?

It depends.  Given that your code violates NMEA expectations, I'm
not going to bother dissecting what gpsd does with broken input.

Here are the first lines of your file, trimmed to the first 2 columns:


Note the time never changes.  gpsd neesd the time to change in order to
know when to compute data, clear data, report data, etc.

Fix your input.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

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