[FOSS-GPS] RTKGPS+ using RTCM with GPS+GLONASS not working

David Kelley DavidKelley at iTSware.net
Sun Nov 15 08:30:28 PST 2015

Several possible issue occur to me reading this,
Can you post 60 seconds or so of the data you are getting from the 
Novatel OEMV/4
Self and others can decode it and determine/confirm if it is valid
 From what you describe, perhaps only GLONASS observations are being sent.

I presume from your description these two units are more or less collocated,
hence same view of sky and RTKLIB is about to get correct ephemeris from 
one of them
Enable the logging (level 2 should do it) and make sure you do not see a 
stream of "no orbit" messages
But if you are getting a 'single' mode fix, i.e. autonomous, then 
RTKNAVI got the orbits from somewhere.

And of course, be very sure you are using 2.4.2 and not 2.4.3 unless you 
rebuilt it with the July leap second added.

A short recap regarding part of the GLONASS issue in RTKNAVI versions:
Recall that GPS notices leap second but does not accumulate them into 
the next GPS week. GLONASS, aligned with UTC, does not need to worry 
about them.  RTKLIB uses posix/unix time internally.  By convention in 
RTCM messages always have GPS messages first and then GLONASS messages, 
then other GNSS types.  A flag in the RTCM observation messages is 
asserted for "more data to come taken at the same measurement interval" 
and when then flag toggles, devices using RTCM know to use all the past 
messages they just got as once set. Typically these two message types 
have the same time stamp.

RTKLIB, like most GNSS software, decodes the input messages into a large 
master array of observation data, and then, when the flag drops, uses it 
(along with the orbital parameters and other data) to run the navigation 
filter.  RTKLIB processes such messages and with each and every message 
set it tests the time stamp for any changes in value (which implies a 
new measurement epoch has started), and then using its own logic 
converts to the posix time it prefers.  It will not correctly 
accommodate the additional offset to the 17th second added in July in in 
the 2.4.3 code base.

So in practical fact the flow of events is: it gathers all the GPS data 
up, puts it in an array, then starts on the GLO data, detects a new time 
stamp, resets the array (the point of error), fill the array with the 
GLO data set, notices the flag has changed indicating no further data at 
this measurement time, and then sends the array (with the GPS data now 
overwritten), to the navigation sections. This is why you see navigation 
with GLO only when you have provided it with GPS+GLO.   And, if only GPS 
is present, there is no overwriting, only incorrect TOW time of by a 

Hope that serves to explain what 2.4.3 does under this condition.

On 11/15/2015 3:50 AM, gto234 wrote:
> Can anyone help me setup the base station on the RTKGPS+? It is a novatel
> oemv board.
> I set the input streams as follows but the result is single mode as if not
> receiving corrections.
> Input Rover
> Format: Novatel OEMV/4
> Antenna: none
> Commands at startup/shutdown: choose the "oem4_raw_1hz.cmd"
> Receiver option: none (what is this field?)
> Input Base
> Format: Novatel OEMV/4
> Antenna: none
> Receiver option: none
> Commands at startup/shutdown: choose the "oem4_raw_1hz.cmd"
> Base station position: enter Lat/Lon/Height manually, there is no "average"
> option.
> Transmit GPGGA to Base Station: OFF (since it is not connected to NTRIP
> caster)
> What am I doing wrong?
> Tried also the RTCM3 Format on the Base as follows:
> Input Base
> Format: RTCM3
> Antenna: none
> Receiver option: none
> Commands at startup/shutdown: choose the "oem4_rtcm3_1hz.cmd"
> Base station position: RTCM Antenna position
> Transmit GPGGA to Base Station: OFF (since it is not connected to NTRIP
> caster)
> This setup results in same problem discribed before with only GLONASS
> satellites in the solution.
> --
> View this message in context: http://open-source-gps-related-discussion-and-support.1099874.n2.nabble.com/RTKGPS-using-RTCM-with-GPS-GLONASS-not-working-tp7573332p7573336.html
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