Re: gpsd hardware with RTK support?

[Gary E. Miller]

Yo Greg!

On Mon, 21 Nov 2022 18:16:55 -0500
Greg Troxel <gdt@lexort.com> wrote:

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

I think the OP asked in relation to gpsd.
 
> > 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.

Yes, an other updates.  BUt, you still gotta check for that compatability.
ORGN, and others, support both.

> > 3. My local ORGN only supports GPS and GLONASS, and a lot are GPS
> > only.  
> 
> Definitely a minus, but that's not "incompatible".

Yes, but limits the utility of getting a multi-constellation receiver.
No point getting a 7 constellation receiver if your RTK is 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.  
> 
> MaCORS can send on various mountpoints (for carrier phase, omitting
> CMR):
> 
>   RTCM 3.x (Extended) : GPS/GLO only
>   RTCM 3.x (MSM4)     : GPS/GLO/GAL/BDS including GPS L5

Only MSM4?  Sad.

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

Yes, but you still need to check, before writing a check.

> >> 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".

Yup, it aint't trivial.

> > 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.

MSM7 has more/better correction data than MSM4.  So for best results,
you want MSM7.

> > 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'm just quoting their manual.  I assume they mean: "works best with".

>  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.

4cm not that great these days.

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

The OP never mentioned what his base will be, so another thing to
check.

> >> 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.

OTOH, most gpsd users have only used their local gov NTRIP, or their own
base station, so we dont have a good way to know.

> 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.

GAL is 6 years old.  6 year old 3G phones no longer work.

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

I expect GGA would help.  Real NTRIP documentation would be nice.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

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    "If you can't measure it, you can't improve it." - Lord Kelvin

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