Re: how to forward RTCM data to gpsd?

[Greg Troxel]

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

> Yo Greg!
>
> On Fri, 11 Dec 2020 20:19:44 -0500
> Greg Troxel <gdt@lexort.com> wrote:
>
>> I wonder why you are only getting GPS from the local station, but
>> presumabbly it's old and not sending Galileo and GLONASS corrections.
>
> RTCM 3 is GPS and GLONASS only.

Perhaps in some trivial spec sense, but my local reference network is
sending MSM4 format for other constellations.  An update read:

7/10/19-     RTCM 3.x (MSM4) single site products introduced.  All RTCM MSM 
(Multi Signal Messages) now include GPS with L5, Glonass, Galileo and BeiDou.

This is with Leica equipment:
  GR30 (receive)
  AR20 LEIM (antenna)

  
https://leica-geosystems.com/products/gnss-reference-networks/receivers/leica-gr50-and-gr30

>> Repeating something I said earlier my local RTCM3 provider is now
>> sending data on all 4 constellations.
>
> Not all 6?

Which do you mean beyond GPS, GLONASS, Galileo and Beidou?

If you mean IRNSS and QZSS, those are regional, not global, and I do not
hear of anyone receiving them in CONUS.   The MassDOT reference station
receivers do support at least QZSS, from the Leica product page - but
the propagation from over Japan appears poor :-)

>>  But it may be also that with 3
>> constellations and the resulting high number of satellites, the SBAS
>> approach is already good enough this doesn't matter.
>
> I have run tests with GPS+SBAS and GPS only.  Both using SBAS correction.
> Adding SBAS to the fix decreases the fix quality.  YMMMV.

I gather you mean "adding the SBAS pseudoranges".  I was talking about
uncorrected pseudoranges from a bunch of satellites vs those same
satellites and also using corrections that arrived via SBAS.  My
impression, not rigorously confirmed, is that using the corrections
helps.

>> It would be nice if receivers were clear about "using corrections from
>> this SBAS" vs "using this SBAS's signal to observe pseudoranges and
>> including those in the position estimate".  It's very natural for
>> someone to expect the using: field of an SBAS satellite to mean that
>> corrections are used.
>
> Some do.  Depending on your u-blox model ubxtool will tell your the
> difference. Plain "used" means the ranges were used.  The DGPS flag
> is set if SBAS or RTCM corrections applies.  So if you have no
> local RTCM, the DGPS flag tells you if the SBAS corrections were used.
> Indepene nt of the "used" flag.

Make sense; perhpas it's not as confusing as I thought.

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