Re: ✘NTRIP and RTCM

[Greg Troxel]

"Gary E. Miller" <gem@rellim.com> writes:

> Anyone wathcing git head, or issue 175, will notice that I have been
> workong on NTRIP.  Still a lot of rough edges, but progrees.

Thanks for posting, because I am not watching...

> See attached one one plots, all from the same ZED-F9P and antenna.
>
> Plain3600.png      -- no corrections
> 23Single3600.png   -- RTCM 2.3 corrections (1 mile away)
> 3Single3600.png    -- RTCM 3 corrections (1 mile away)
> MAX3600.png        -- "MAX" synthetic RTCM 3 correction.

That's really interesting.  I am guessing:

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

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

  MAX: carrier phase reference data with RTK FIX

> 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.

> The CEP(50)s:
>
> 0.764m   Plain3600.png
> 1.149m   23Single3600.png
> 0.719m   3Single3600.png
> 0,044m   MAX3600.png
>
> Things to note.
>
> 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.

> b) RTCM 3 was barely better than no corrections

That's surpising, as for me being in RTK FLOAT is better than unaided.
Do you have SBAS disabled, so it is really "no corrections".

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

> 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.

> u-blox just announced a commercial sat based correcton service that will
> beam corrections to any paying customer.  TBD if their corrections are
> useful, or if normal people can afford them.

I bet the answers are yes and no.


What I would find really useful is:

  record fix mode with each point as metadata

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

  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.


I am curious what antenna  you are using.  I have a beitian one that
used to be about $90 various places, and an ardusiple "calibrated 2-band
antenna".   But the F9P is not using the cal file.



What I don't understand is why you aren't able to get into FIX with a
single reference a mile away.    My closest reference is much further,
and I use "iMAX".

I am curious how many constallations ORGN is providing data for, and if
it's MSM4 or somethihng else.    MaCORS is doing MSM4 and they include 4
constellations, having recently just added BeiDou.   Hving Galileo is
huge as they have a decent number of sats and all are usable on L2.
With GPS you can only use the ones that have L2c.

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