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Re: gpsprof: higher resolution

From: Gary E. Miller
Subject: Re: gpsprof: higher resolution
Date: Sun, 16 Aug 2020 14:08:30 -0700

Yo John!

On Sun, 16 Aug 2020 16:56:17 -0400
John Ackermann N8UR <> wrote:

> > To get the most from the F9P requires binary messages, not NMEA, and
> > fiddling with the sentence mix.  
> What I'm seeing in the GGA sentence from any of the receivers that
> have the NMEA HIPREC config option is seven decimal places following
> the minute:
> $GNGGA,134648.00,3943.7111969,N,08410.6922079,W,4,12,0.74,280.601,M,-33.483,M,1.0,0073*5C

Yeah, that is "High Precision Mode" for NMEA.   But the default
u-blox configuration does not do that. gpsd/ubxtool do not configure
that mode.  So many ways to misconfigure NMEA on the u-blox.

> which ought to translate to about 9 digits of precision.

Yup.  But then you add in converting to ASCII and back for further
loss of precision.  Either way, except for very short (zero!) baseline
RTK that is swamped in the noise.

Testing zero baseline RTK seems to me not useful in the real world.

> BTW, I discovered that while the only 8-series receiver to support
> NMEA HI PREC is the M8P, all three units of the 9 series that I've
> tested (M9N, M9P, and M9T) support it.

I expect when they figure out how to make them in volume at a reasonable
price they will cripple the cheaper versions.

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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