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Re: ✘PX1172RH_DS performance

From: Gary E. Miller
Subject: Re: ✘PX1172RH_DS performance
Date: Tue, 5 Apr 2022 17:24:52 -0700

Yo Greg!

On Tue, 05 Apr 2022 19:46:43 -0400
Greg Troxel <> wrote:

> "Gary E. Miller" <> writes:
> > The part includes 2 RTK GNSS and you connect two GNSS antennas to
> > it. You take RTCM3 from a "fixed base" and feed it to this parts
> > "moving base".  Then the part computes distance and angels to its
> > built in "rover".
> How many angels fit on a GPS antennas?

Which until recently, was as good a question as any, but with
UBX-MON-SPAN w can better tell antennas apart.  In addition to the
obvious differences in SNR.

> I see the point of two antennas so you can have them at some fixed
> separation on a vehicle and obtain orientation.

Only those that have played with 9 axis IMU truly appreciate how
much simpler a GNSS "compass" is.

>  And I can see the
> point of RTK from a base/network to get coordinates for the primary
> antenna location.

CEP(50) of 0.007 m over 12 hours speaks for itself.

> (Then you can also get position for the "azimuth
> mark" (2nd antenna) as it might be called for passive control.)  So
> questions:


>   What are you using for fixed base?

I use ORGN.

Another nice thing of the part is they give you that, and "cgps --rtk"
shows it.  But I don't have an RTK solution at the moment, not sure why.
The baseline is about 2.2 km.

>   I think your plot is for position from the primary antenna, and you
>   are not showing data from the secondary antenna.  Is that right?

Right.  gpsd has no (easy) way to plot that yet.  UNtil last week gpsd
could not even collect the data, much less put it in the JSON.

>   Can it do azimuth without any incoming RTCM3?

Yes.   I was told RTCM3 helps, but I have no data on that yet.

>  Basically use one as
> a moving base, with position determined from navigation solution, and
>   compute the vector between them, and have precise oritentation even
> if position is fuzzy at the 5m level.


> > Actual 2D error:
> > Actual Alt error:
> 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/

> I am 99% guessing
> that you don't have a mm-level position for the APC,

Uh, what is APC?  

> and thus these
> are the values relative to the average position.

Yes, as required in RCC-261-00/

> One could, for a
> fixed roof antenna, do
>   raw observations for 24h and use PPP (both?)

Done that, not with this part.

>   raw observations for 24h (same bits) and use OPUS

OPUS is not available where I live.

>   Use F9P with ORGN baes

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.

>   Use PX1172RH_DS with ORGN baes

Which is what I did.

> and compare them all.

So much to do, so little time...

> > But this perforrmance is not easy to get.  Not just any antennas are
> > good enough.  I had to sort for my 2 best L1/L2 antennas.  Even
> > then a good skyview was not sufficient.  I only acheived RTKFIX by
> > putting the antennas on top of my roof.
> I find that getting into FIX mode depends a lot on sky view.

Thus the need for the roof mount.  Which makes it not very practical
as a mobile application.

> 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.

> With a 20 degree treelne at the horizon it is rapidly and solidly in
> FIX.  On trails in the woods, iffy but FIX can be achieved at times.
> There is a new firmware for F9P that I need to update to and it is
> rumored to be a lot bettter.

I'll hahve to grab that.

> > Figuring out how to test the "compass" part will take some work.
> I guess that answers my question above - you did what I would have
> done first.

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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