Re: ppp averaging and circular error of probability

[Gary E. Miller]

Yo gpsd---!

On Fri, 9 Sep 2022 22:00:16 +0200
gpsd--- via <gpsd-users@nongnu.org> wrote:

> environment
> hw: raspberry pi4, Ublox ZED-F9P Expansion from uputronics
> sw: Debian bullseye, gpsd: 3.24.1~dev (commit 
> 9c5c09a7b049c4e5b65470aa2ef65c0295e98007)

Cool.

> I run PPP in averaging mode several times as described in 
> https://gpsd.gitlab.io/gpsd/ppp-howto.html or "man gpsprof" with 
> different number of fixes. I did it for 6 hours, 1 day and 2 days.

Good.

> When I display the result is see for example results like this:
> 
> CEP 50% = 0.6m , CEP 95% = 1.1m , CEP 99% = 1.9 m

Yeah, that is about what I would expect.

> Recently I run it for 3 days and I got a strange result:
> 
> CEP 50% = 0.595m , CEP 95% = 1.469m , CEP 99% = 1.423m

Why does that look strange?  Their are long term errors in GNSS that
only show up over long time periods.  Sun spots, ionsphere effects,
etc.

> How can it be that the probability for 99% is smaller than for 95% ?
> In a sense of statistics not possible.

That is an odd one.  I assume from gpsprof?  If so, send me tha raw data
and I'll look at it.

> If someone is interested I can also support the 10mb plot file.

I would prefer the raw data, then I can make my own plot file and
see for myself.  Maybe even fix it.

> I also calculated the distance between the different results. They
> are all below 4 cm. So I am not sure if this CEP gives a useful
> information at all.

My mind reading is not good at this distance.  Can you show your work?

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

pgp3Xa3oji0NK.pgp
Description: OpenPGP digital signature