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Re: ✘PX1172RH_DS performance

From: Gary E. Miller
Subject: Re: ✘PX1172RH_DS performance
Date: Wed, 6 Apr 2022 12:05:15 -0700

Yo Greg!

On Wed, 06 Apr 2022 10:05:57 -0400
Greg Troxel <> wrote:

> >> It is not really error, but a meaure of variance.
> >
> > It all depends on how you define things. "error", as in Circular
> > Error Probability (CEP) was defined by other people before I got a
> > chance to complain.  gpsd uses the terms and equations from
> > RCC-261-00/
> OK on RCC-261-00 but there is still an important difference between
> spread relative to average and spread relative to the correct answer.

Where do I find ground truth for 7mm, when my local CORS wanders over 1cm
in each direction?

> >> I am 99% guessing
> >> that you don't have a mm-level position for the APC,
> >
> > Uh, what is APC?  
> Antenna Phase Center.  The physical location whose position is
> actually determined by a GNSS receiver in the most straightforward
> setup.  On better antennas, this is specified relative to an Antenna
> Reference Point (ARP), which is something you can physically access
> to measure. Typical ARP is horizontally the center of the 5/8 thread
> and the vertically "Bottom of Antenna Mount".

Oh, yeah.  I can'f afford those antennas.

> Getting more hard-core, there are antenna calibration files and the
> APC varies with satellite elevation and sometimes also with azimuth.

Even ORGN is not that hard core.

> >> One could, for a
> >> fixed roof antenna, do
> >> 
> >>   raw observations for 24h and use PPP (both?)
> >
> > Done that, not with this part.
> So you could plot that alongside these values and see if PPP and the
> center of the RTK line up.

When I get around to doing a PPP from the current setup, compare it with
other PPP on the same location, code up new plots, etc.

So much to do, so little time.

> >>   raw observations for 24h (same bits) and use OPUS
> >
> > OPUS is not available where I live.
> Really?   OPUS takes raw L1/L2 files and calculates positions based on
> NOAA CORS Network stations.  I am 99% sure it works anywhere in CONUS.
> Maybe they are too far away to get really good positions.

There is only one CORS station within 100 miles of my position.  Not
enough for OPUS to try to do a PPP.

> > No F9P in this setup.  I just use ORGN as the fixed base.  I'm not
> > gonna worry about improving on 0.007 m for a while.
> My point is that 0.007 m is relative to self average and you don't
> know how accurate that average is.  If you have the antenan and cable
> you can swap in the F9P and log raw for 24h, while also logging
> output from RTK.q

But then I have to stop work on the Skytraq.  So, eventually.

> >>   Use PX1172RH_DS with ORGN baes
> >
> > Which is what I did.
> >
> >> and compare them all.
> >
> > So much to do, so little time...
> Sure, your time, your call.  I am just cautioning not to treat
> RCC-261-00 "error" as error, when it is a measure of self consistency
> instead.

As a programmer, I never take "names" literally. then are just handles
on a vaiable.  The CEP is one of the very earliesst geodetic "error"
computations of any kind.  It predates even longitude.  In my mind, it
have great-grandfather rights to the term as they use it.

So call it what you will, I'll call it CEP().

> > Thus the need for the roof mount.  Which makes it not very practical
> > as a mobile application.
> I haven't tried it on a car yet, but walking around in places without
> a lot of trees works well, with MaCORS.

But you have an F9P, and this is a PX1172RH_DS.  Apples and organges.

> >> And,
> >> one's base having more constellations helps make it work better.
> >
> > ORGN is just GPS and GLOBASS.  This part can use BeiDou, GALILEO,
> > etc.
> MaCORS has 4 constellations.  Having more satellites really helps.
> I suppose you could run your own base with an F9P.

So much to do, so little time.

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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