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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" <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.
> 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
CMR):
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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