Re: ✘NTRIP and RTCM

[Gary E. Miller]

Yo Greg!

On Fri, 03 Dec 2021 08:53:12 -0500
Greg Troxel <gdt@lexort.com> wrote:

> That's really interesting.  I am guessing:

Glad you liked it.

>   RTCM2.3: these are pseudorange corrections, perhaps GPS only?

Yes, GPS only.

>   RTCM3: these are carrier phase reference data, and it looks like
> your device was in FTK FLOAT

Dunno, I have not dug into the data.

>   MAX: carrier phase reference data with RTK FIX

Ditto.

> > All from the Oregon ORGN network.  Many thanks to them for allowing
> > me cess.  
> 
> Indeed, it's very nice of the states to allow public access.  MassDOT
> runs MaCORS which anyone can use.

Still not as easy as many other countries.

> > a) RTCM 2.3 made the CEP(50) worse!  
> 
> I am fuzzy but I gather that RTCM2.3 typically is pseudorange
> corrections, and GPS only.  It may be L1 only.

Yes, in this case, GPS and L1 only.

> > b) RTCM 3 was barely better than no corrections  
> 
> That's surpising, as for me being in RTK FLOAT is better than unaided.

It is what I have seen for years.

> Do you have SBAS disabled, so it is really "no corrections".

I do not have SBAS disabled, but that F9P rarely uses it.  SNAS is
almost exactly RTCM 2.3

> Also, while I see your point about averages being not better, the
> character of the wander is very different.

Yeah.  The high frequency noise is gone.

> This is what RTK FLOAT
> looks like for me (usually viewed in Vespucci in Android, which I use
> for a field data collector).  RTK fixed looks like a dot.

I'll watch for that.

> > c) The synthetic corrections are just WOW.  
> 
> Indeed, and you can see the resolution of the coordinates which looks
> like most of 1 cm.  I wonder if this quantization is in the raw logs
> or if it could be in the analysis chain.

I'm running in normal mode, with none of the "High Precision" messages.
Moany of the UBX-NAV-PVT data items are in mm.  Worth a test.

> What I would find really useful is:
> 
>   record fix mode with each point as metadata

I have all the raw data.  Nothing more can, or could, be recorded.  And
it is all 3D.

>   carry that through analysis and color the dots based on
>   autonomous/differential/RTK-fixed/RTK-float

u-blox is bad at reporting that.

>   be able to use an input position in the analysis instead of the
>   average.  I bet your tight value in fix is pretty much right.

Lost me.  Explain?

> I am curious what antenna  you are using.

The u-blox one, in a window sill.

> What I don't understand is why you aren't able to get into FIX with a
> single reference a mile away.

I don't know if I can or can't.  But that is my long term experience, and
other see simiilar.

> My closest reference is much further,
> and I use "iMAX".

Do you have doc on "iMAX"?

> I am curious how many constallations ORGN is providing data for, and
> if it's MSM4 or somethihng else.

I'll look at that data next week.  I captured everything.  Only last
week would gpsd even log that data.

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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