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Re: gpsd hardware with RTK support?

From: Gary E. Miller
Subject: Re: gpsd hardware with RTK support?
Date: Mon, 21 Nov 2022 13:52:15 -0800

Yo Greg!

On Mon, 21 Nov 2022 12:16:59 -0500
Greg Troxel <> wrote:

> "Gary E. Miller" <> writes:
> > Depends.  If you base and rover are both ZED-F9P, then sure.  But
> > many public RTCM3 feeds are not u-bloz compatible.  
> Can you give some specifics of this?

That's the problem, there are a lot of specifics.  To name a few:

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

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

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

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.

> I found that the F9P worked with
> most of the variants from MaCORS.

Surprising.  I'm not so lucky with ORGN.

Specific to the F9P:

1. It only supports MSM4 and MSM7.  That leaves a lot of possible
incompatible configurations.

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.

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.

> 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.

We could go on but that shows some of the various compatibility issues
that quickly arrise with RTK.

> but a service with only that seems ancient/broken.

At the rate RTCM3, and other proprietary NTRIP protocols are moving,
ancient/broken happens quickly.

>  Do the ones you refer to use some proprietary messages types?  Which
> ones?

I'm not sure what you mean when you say "you refer"?  I don't recall
making any recommendations ore specific references.  Just whinging
about the terrible state of RTK.

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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