Re: ✘PX1172RH_DS performance

[Gary E. Miller]

Yo Greg!

On Wed, 06 Apr 2022 16:17:53 -0400
Greg Troxel <gdt@lexort.com> wrote:

> > Where do I find ground truth for 7mm, when my local CORS wanders
> > over 1cm in each direction?
> 
> If you get position a different way and it's within 1 cm of the
> average, you call that great.  But until you compare you don't know.

So much that I don't know.  My current plan for this summer is to do
a whole day on top of a USGS monument.

> >> 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.
> 
> This one is under $200; it's the low end of calibrated.
>   
> https://www.ardusimple.com/product/calibrated-survey-gnss-multiband-antenna-ip67/

Still only makes sense if I do a lot of things that use the calibration
files, like PPP.  Which I do not.  Yet.

> >> 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.
> 
> I find that very surprising.

Ditto.

>  I would expect that the reference
> stations are using something like Leica or Trimble

Yes.

> and have
> calibrated antennas and are using ANTEX cal files in their base
> setup.

Maybe they do, but their RTCM3 broadcasts that they use the "NULL"
calibrated antenna.

>  The APC is usually a few cm higher than the ARP, so you need
> to take that into account to get cm-level heights.

hard to be a few CM higher when the entire height of the anteann
case is on 2 cm.

> >> > 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.
> 
> That's surprising. 

Maybe to you.  Not to us near the middle of nowhere.

>  But OPUS does not do PPP.  It does carrier phase
> differential.   Are you saying that you took a L1/L2 24 hour raw file
> in RINEX and you can process that with NRCAN PPP but if you submit to
> OPUS it fails?

Yup.  OPUS does not fail, they refuse to even try.

> >> > 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.
> 
> They are basically the same architecture: dual-frequency with RTK
> code. I would expect similar performance.

Then your expectations are off.

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

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