Re: [gpsd-users] Does GPSD support RTCM corrections via Internet?

[Gary E. Miller]

Yo Bo!

On Thu, 03 May 2018 10:35:44 +0200
Bo Berglund <address@hidden> wrote:

> To clarify:
> I would like to know if GPSD can apply the corrections received from
> the server to the positions received from the GPS unit via the
> standard NMEA messages.

No, not possible.

> I.e. can it work *without* sending anything
> into the GPS unit itself?

No.  Not presently.

> I am planning to use a GPS module hooked into a Raspberry Pi which is
> networked and am hoping to get better accuracy by applying the
> corrections.

You will get better RELATIVE accuracy with the corrections.  You will
not get better ABSOLUTE accuracy with the corrections.  The RasPi can
easily upload the RTK data to the rover for you.

There is a simple reason why gpsd can not apply RTK corrections to the
NMEA messages.  NMEA message do not contain the required psuedo range
and carrier phase data that the corrections get applied to.  Otherwise
known as the raw data.

A very few GPS do output the the raw data required.  Only in
proprietary sentences.  Since it is trivial to send the RTK data
from the base to the rover, and have the rover do the math, no one
has bothered to decode the vendor specific raw data in gpsd yet.  Much
less do any math on it.

I have a modest pile of different GPS units.  Only my Skytraq NS-HP
outputs the raw data.  I have a u-blox NEA-M8T on order that also can
output the raw data.  The commonly used GPS, including common u-blox, do
not output raw data.

Note that PPTK is a different animal, it does improve absolute accuracy,
but still requires the raw data.  Then you convert the raw data to RINEX
format and upload it to a post-processing service.

Some other GPS programs (Lady Heather, u-center) now can take raw
data from the GPS and output RINEX data.  I hope that gpsd gets that
capability this year.

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