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Re: [gpsd-dev] [Patch Submission] $GPVTG w/magnetic course

From: Gary E. Miller
Subject: Re: [gpsd-dev] [Patch Submission] $GPVTG w/magnetic course
Date: Wed, 13 Jun 2018 15:58:27 -0700

Yo Gerry!

On Wed, 13 Jun 2018 17:39:45 -0500
Gerry Creager - NOAA Affiliate <address@hidden> wrote:

> > > VTG implies at least a 2D lock because it cannot determine
> > > velocity or track without at least the 2D data.  
> >
> > More and more modern GPS now include IMUs.
> >  
> Agreed. It was but a matter of time. That said, a half-decent IMU
> should be able to at least temporarily substiture for a 2D fix and
> also discipline the GPS solution. But that depends on the
> vendors/manufacturers to have a clue about what they send out to
> people, doesn't it?

Well, some vendors I looked at, like u-blox, do tell you in the
GPVTG is there is at least a 2D fix.  Others, like Trimble, do
not.  So shame on the ones that do not.

That's what makes this so fun!

> > You will not find one.  NMEA standards are very expensive and they
> > defined their copyright vigorously.  Better to look at several
> > GPS vendors doc on how they implement GPVTG.  
> I'm lookin'. It's a non-trivial university, and I might even get the
> Library to order one. For that matter, I might get the Lab to order me
> one... I can almost justify it. I'm well aware of the copyright
> protection. A friend sat on NMEA committees and couldn't even discuss
> some of the topics of discussion.

I'd love it if you got one.  Then you could be our NMEA expert.

Next get the GPS makers to order copies.  :-)

> I started, prior to sounding off, by looking at some of the vendor
> docs. Noticed they're all still a bit opaque.ublox isn't too bad;
> Trimble isn't too useful, as examples.

And the best examples are the gpsd test cases.  Real world data.

> Recall the old saying about standards: Nice thing about 'em is
> there's so many to choose from. Or in this case, so many ways to
> misinterpret to your own advantage. Makes writing code hard.

Writing code is easy.  Good code is hard.  :-)

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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