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Re: [gpsd-users] using NTRIP/RTCM23 with gpsd

From: Gary E. Miller
Subject: Re: [gpsd-users] using NTRIP/RTCM23 with gpsd
Date: Fri, 2 Nov 2018 11:00:05 -0700

Yo Mark!

On Fri, 2 Nov 2018 14:50:58 +0000
Mark Jablonsky <address@hidden> wrote:

> We've recently subscribed to a NTRIP service and have set it up with
> gpsd by adding the NTRIP source to the gpsd device list. Our module
> that we are working with has support for RTCM23, so we have connected
> to the RTCM23 mount point for our NTRIP service.  We can see in cgps
> that we are receiving RTCM23 data packets, but it doesn't seem like
> it has done anything to improve accuracy.  

You are leaving out a lot of important details:

1. what version gpsd?

2. installed from source or a distro package?

3. what is the command line used to start gpsd?

4. what GPS receiver model?

5. how close is the NTRIP/RTCM source to you?

Regardless of those answers, I would not expect NTIP to help you at all.

All gpsd does is pass on the data it gets.  gpsd does not do anything
with RTCM2 or RTCM3 data, except pass it on to the user.  It does not
pass the RTCM2 or RTCM3 to the GPS.

For RTCM2 or RTCM3 to improve the GPS fix quality, the RTCM2 or RTCM3
data stream must be input into the GPS receiver.  gpsd does not do that,
nor does gpsd know how to do that.

> So I am unsure whether or not we have to do anything externally to
> get the advertised improved accuracy of ntrip, or should gpsd already
> be handling that on its own.

RTCM2 is an obsolete technology that adds no value to modern GPS.
If your GPS is seeing an SBAS satellite then it already has RTCM2
equivalent correction data.

RTCM3 is a little better, assuming you are getting RTCM3 data from a
nearby base station.  The few GPS receivers that I have that can use
RTCM3 data require that the data be input to the GPS on a 2nd serial
port.  I just cable up the RTCM3 output from my base GPS 2nd serial port
to input into my rover GPS 2nd serial port.

There may be some way that gpsd can help that process, but it would be
very model dependent and no one has done that work, yet.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  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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