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Re: gpsd hardware with RTK support?

From: Greg Troxel
Subject: Re: gpsd hardware with RTK support?
Date: Mon, 21 Nov 2022 18:16:55 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (berkeley-unix)

"Gary E. Miller" <> writes:

> 1. as you mentioned, the syntehic feeds need GGA, which gpsd does not do.

Which is simply a missing feature in gpsd.   Ardusimple and sparkfun
arduino code both do it.  I'll try to figure it out and post a pseudospec.

> 2. There is the obvious RTCM 2 vs RTCM 3 incompatibility.

As I understand it, more or less non-deprecated RTCM2 is for
differential (pseudorange errors and pseudorange rate errors) and RTCM3
is the normal method for carrier phase reference data.  I am actually
not aware of carrier phase in RTCM 2 or regular differential in RTCM 3.

> 3. My local ORGN only supports GPS and GLONASS, and a lot are GPS only.

Definitely a minus, but that's not "incompatible".

> 4. Less obvious is all the RTCM3 versions.  Does your base send MSM1,
> MSM2, MSM3, MSM4, MSM5, MSM6 and/or MSM7?  Does that match the RTCM3
> version of your receiver?  Other RTCM3 messages are similarly multiply,
> and incompatibly, versioned.

MaCORS can send on various mountpoints (for carrier phase, omitting

  RTCM 3.x (Extended) : GPS/GLO only
  RTCM 3.x (MSM4)     : GPS/GLO/GAL/BDS including GPS L5

and that's it for now.  My impression is that MSM4 and MSM7 are common,
and the other ones much less so.

>> I found that the F9P worked with
>> most of the variants from MaCORS.
> Surprising.  I'm not so lucky with ORGN.

I went back and looked.  There is CMR that I never tried, and there is
pre-MSM RTCM3 that I didn't try.  I have run MSM4 in both single site
and i-MAX, and iMAX works better.   So "works with most" isn't really
true, but "for each kind of reference data (near, single-site, i-MAX)
there is a compatible encoding which is easy to select".

> Specific to the F9P:
> 1. It only supports MSM4 and MSM7.  That leaves a lot of possible
> incompatible configurations.

True but I wonder how many utility-type (state DOT or commercial
service) does MSMn for n != 4/7 and does not do 4 or 7.

> 2. The F9P wants the u-blox secret 4072.0, 4082.1 messages.  Unless your
> base station is a u-blox, it can not send those.

I am not sure what you mean by "wants".  I am using MaCORS which is
Leica and I go into FIX very easily (given good sky view) and have
observed 4 cm repeatability when occupying the same mark days later.

4072.0 is about moving base.   For geodetic-quality RTK networks the
antennas are mounted in concrete or something like that.

> And you'd think the F9T would be the same, right?  Wrong.  The F9T
> supports toe 4072.1 message, but not the 4072.0 message.

that's funny.

>> I would not expect it to work
>> with CMR and CMR+,
> Yup, but since those are also NTRIP srouces for RTK usage, the user needs
> to beware.

Sure.  What I meant is that I do not have the impression that there are
lots of reasonably well-run, otherwise reasonable RTK correction
services that work with lots of receivers but fail with F9P.

It does seem that there is an installed  based of RTK networks that are
GPS/GLO only.  That's not really ancient as GAL is recent.

I still am surprised your ORGN experience isn't better.   If they do
VRS,  then GGA will help.

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