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Re: gpsprof: higher resolution

From: Gary E. Miller
Subject: Re: gpsprof: higher resolution
Date: Sun, 16 Aug 2020 13:41:25 -0700

Yo John!

> That's very interesting, Gerry.  I was aware that there is some 12
> and 24 hour periodicity that can affect averaging, but not of the
> mid-term noise.

The GPS sats return to the same position every 12 hours.  So averaging
over 12/24/36/48 hours removes odd orbital harmonics.  gpsprof
shows this effect.

> The averages I'm using for this set of tests are the values
> calculated by gpsprof.  I don't know if that does any decimation or
> not.

Nope.  gpsprof uses all the data it collects.  No 'decimation'.  Depending
on your definition of 'decimation', there is low pass filtering in applied
to the data.  That defeats the purpose of gpsprof in show how wild the
data excursions can be.

gpsprof does not care if the data came to gpsd as NMEA or binary.  gpsprof
just uses the gpsd JSON.  Often, but not always, the binary has more
digits of 'precision' than the NMEA.

For the u-blox F9P: RELPOSNED is 1mm precision, and HPPOSLLH is 9
decimal degrees of precision.

For other 9-series POSLLH is 7 decimal digits of fractional degrees.

For the 9-series xxRMC is ddmm.mmmmm, which is about 6 decimal digit or

To get the most from the F9P requires binary messages, not NMEA, and
fiddling with the sentence mix.

And that is just the start of complications.  Some days have "good"
atmospheric conditions, other days not so much.

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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