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how to forward RTCM data to gpsd?
From: |
Kristoff |
Subject: |
how to forward RTCM data to gpsd? |
Date: |
Wed, 9 Dec 2020 02:05:09 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 |
Hi all,
I am new to the mailing-list, with just a quick question.
Can somebody provide a quick overview of what gpsd expects RTCM messages
should look like?
As part of an exercise to learn Software Defined Radio and GNU Radio, I
"build" a receiver in GNU Radio for the marine DGPS radio-stations in
the mediumwave band, including some python-code to decode the RTCM
messages. (not yep posted online .. first code-clean-up :-) )
So, as I now have that, I guess it would be fun to actually use this
RTCM data for something useful, e.g. feed it into gpsd so it gets
forward to my ublox GNSS-receiver.
My plan is to write a small TCP-server in python and let dgps connect to it.
Now, the question is, what is the format for RTCM messages should look like?
I have done a quick scan of the source-code of gpsd, so can somebody
confirm these three assumptions?
1/ RTCM messages are 30 bits (i.e. they do not match the byte frames of
TCP/IP).
Am I correct to assume that I can just stuff the RTCM databits into a
non-structured stream -ignoring byte-boundaries- and that gpsd is able
to take care of frame-synchronisation?
2/ The marine DGPS radio-service uses bit-inversion (i.e. all databits
of the RTCM word are inverted if the bit proceeding that word is 1).
I do not know if this so for all RTCM messages. or if this is something
specific for the marine DGPS service.
But I did find a reference to bit-inversion in the source-code so I
guess that gpsd does expect the RTCM bits to be as received from the
radio (i.e. not bit-inversion corrected).
Is this correct?
3/ is the data expected to be MSB or LSB first?
On a more general point, what would be the best strategy when relaying
DGPS/RTCM packets from a radio to gpsd?
Just stuff the bits as I receive them from the radio to gpsd?
Or first do some filtering / error-checking first myself, and only send
"validated" data to gpsd?
Thanks for any advice.
Cheerio! Kr. Bonne (on1arf)
- how to forward RTCM data to gpsd?,
Kristoff <=
- Re: how to forward RTCM data to gpsd?, Gary E. Miller, 2020/12/08
- Re: how to forward RTCM data to gpsd?, Kristoff, 2020/12/09
- Re: how to forward RTCM data to gpsd?, Gary E. Miller, 2020/12/09
- Re: how to forward RTCM data to gpsd?, Kristoff, 2020/12/09
- Re: how to forward RTCM data to gpsd?, Kristoff, 2020/12/11
- Re: how to forward RTCM data to gpsd?, Gary E. Miller, 2020/12/11
- Re: how to forward RTCM data to gpsd?, Greg Troxel, 2020/12/11
- Re: how to forward RTCM data to gpsd?, Gary E. Miller, 2020/12/11
- Re: how to forward RTCM data to gpsd?, Greg Troxel, 2020/12/12
- Re: how to forward RTCM data to gpsd?, Gary E. Miller, 2020/12/12