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Re: moving to 8 digits of lat/lon (gpxlogger, maybe elsewhere)?

From: Gary E. Miller
Subject: Re: moving to 8 digits of lat/lon (gpxlogger, maybe elsewhere)?
Date: Thu, 3 Sep 2020 11:59:37 -0700

Yo Greg!

On Thu, 03 Sep 2020 14:48:03 -0400
Greg Troxel <> wrote:

> I newly have an F9P, and have gotten it to work in RTK mode with the
> MaCORS ntrip server, just by adding the ntrip:// URL with a mountpoint
> for MSM, single base, specific station sort of nearby.  At least, the
> "no RTK" light goes out, and the position wander as seen in josm
> pointing to gpsd is very small, less than 1m p-p over a few hours,
> indoors.

Cool.  I have not had such luck with NTRIP a mile away...

> I noticed that gpxlogger prints only 6 fractional digits of lat/lon.
> This is 10cm, and I was seeing many adjacent samples with the same
> values.  RTK receivers are making cm-level claims for accuracy, and
> short-term stability may be better.

And some u-blox reports lat/lon to 1e-9 degrees and altitude to 0.1

> I would like tooling and data pipelines never to be the limiting
> factor for accuracy in any analysis, so I'd like to change gpxlogger
> to use 8 digits, to be roughly 1 mm of precision.  I am not aware of
> any spec reason that is prohibited or would cause trouble, and I
> don't expect it to bother other people?

What gpxlogger reads (gpsd) would also have to move to $.8f, so the
JSON has enough data for you.  Then the other clients.  So a total
rebuild of all the regressions, which is actually pretty simple to do.

> And, this is a general proposal that whenever anything in gpsd does
> lat/lon, it uses %.8f, basically, and %.3f for height (in meters of
> course, and hence mm).

Works for me.  Maybe even %.9f degrees and %.4f meters, so we don't need
to do again soon.

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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