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Re: [gpsd-dev] [PATCH] [log.chk] [TPV timing] implement $GPVTG message,

From: Gary E. Miller
Subject: Re: [gpsd-dev] [PATCH] [log.chk] [TPV timing] implement $GPVTG message, and proper timing for output "TPV" messages
Date: Thu, 17 May 2018 14:12:24 -0700

Yo teyrana!

On Thu, 17 May 2018 17:02:03 -0400
teyrana <address@hidden> wrote:

> >
> > On Thu, 17 May 2018 13:31:06 -0700
> > "Gary E. Miller" <address@hidden> wrote:
> >  
> > > GPVTG does say track, not heading, yet you are putting your data
> > > in 'track'.  
> >
> > Whoops.  I meant:
> >
> > GPVTG does say track, not heading, yet you are putting your data in
> > 'heading', not 'track'.
> >  
> Huh?  I don't follow.
> This patch reports track and speed.

Was the heading already there?

> {"class":"ATT","heading":185.39}

> Because that's all the VTG message contains.

Uh, no.

It reports track in true AND magnetic.  It reports Speed in knots and

> The $GPHDT messages are handled by stock gpsd-3.17 code--- which i'm
> branching off.

Ah, sorry, I missed that.  I deleted you earlier ouput, can you resend?

> Currently, GPVTG does not trigger an end-of-cycle.  Should it?

Depends on whether it is at the end of the cycle.  Is it?  If you know it
is not, then it should NOT use REPORT_IS.  But if in doubt use REPORT_IS.

A hard call.

> 3.  Do gps receivers ever report data after it has lost fix?
> In other words, how does reporting data (course & speed) *not* imply
> some sort of location fix?
> +  if (session->newdata.mode < MODE_2D) {
> > +      session->newdata.mode = MODE_2D;
> > +      mask |= MODE_SET;
> > +  }  

Look at that code, you just told gpsd you have a 3D fix.

> Sure, reporting loss of mode is worth reporting.  I'm just not clear
> on why a receiver would report track and speed after it had lost fix?

It should report an invalid track and speed after loss of fix so the
user does not think an old fix is still valid.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  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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