rtknavi no fix / not enough double-differenced residual

[hans-mayer]

Dear All,

I try to setup a rover with a ntrip client.
My environment: I have an U-blox ZED-F9P-02B as GNSS receiver connected to RaspberryPi with Debian 11.11 .
The F9P has FWVER=HPG 1.13 and PROTVER=27.12
Attached is an antenna HAB-ANN-MB-00-00 at the top of the roof of my house.
On F9P I enabled BINARY , RAWX and SFRBX
I enabled GPS and GLONASS all other GNSS are disabled.

I use RTKLIB from https://github.com/rtklibexplorer/RTKLIB with the latest commit 75a2e56

To connect to the F9P I run:
str2str -in 'serial://ttyS0:115200#ubx' -out 'tcpsvr://:10000'

On rtknavi_qt I configured as input streams:

1/rover , TCP client with IP 127.0.0.1 and port 10000 , format U-blox UBX
2/base station, NTRIP client from rtk2go.com port 2101 mount point AUT_VIE_27 with user-id and pwd, format RTCM3

I tried to use also other caster respectively other mount points.

When I start rtknavi I see after short time satellites from rover and base in different colours.
But I never see a fix and therefor also no location.

When I open the monitor I see in one second intervals:

not enough double-differenced residual, n=0

I also realised, whenever I try to define an output stream I get a bind error (99) indepetent which port I use.

When I stop str2str and start gpsd and run xgps I get immediately a fix.

Any help is greatly appreciated.

Kind regards
Hans

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[hans-mayer]

Dear All,

In the meantime I realised that position mode "Single" works but no other mode. Reading the docs I see in mode "Single" there is no correction. Any ideas what I have done wrong ?

When I check the monitor I see "initial base station position error"

When I select "Get Mountpoints" and look for "Mountpoint Options" then it looks quite good.

But when I press "OK" and open a second time "Mountpoint Options" then I get this

And this happens not only with this mountpoint.

Any help is greatly appreciated.

Kind regards
Hans

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[JensReimann]

Tim (rtklibexplorer) pointed my to the issue you found with the "Mountpoint options" dialog in rtknavi_qt.
I think, I found the issue, which was just a small ';' missing in generating the mount string. Could you please try the latest git version and report if it solves the issue?

Thanks for reporting,
Jens

[hans-mayer]

Hi Jens,

Many thanks for this fix. Yes, works perfect.
I hoped this would solve my problem too but unfortunately it didn't. The issue is, when I look at the ground track screen in rtknavi_qt then the current position "walks" around several meters. But I have a fixed mounted antenna.
The setup and config is the same as I wrote in my initial posting. All other settings I left as original. Do you have any idea what it could be ?

Kind regards
Hans

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[rtklibexplorer]

My best guess is that you do not have the base station position option set correctly for RTK solutions. In the Positions tab under the Options menu, you want the base station position option set to RTCM/Raw Antenna position. This will tell RTKLIB to use the base station position in the base RTCM stream. If this doesn't work, I have some additional debug tips in this post

[hans-mayer]

Hi rtklibexplorer,

many thanks for this hint about the RTCM/Raw Antenna position.
This solved an issue.

Now I have now solutions most of the time with "FLOAT". But I am still wondering about the position. I assume I have still done something wrong. When I look at the Ground Track or open the Plot GUI then I can see that the position "walks around" over several meters ( but my antenna is fix mounted on the top of the roof of my house. ) Several meters seems to be too much for me for solution "FLOAT". I assume both graphs should show the corrected position by the base station with NTRIP client.
But for me it's the impression that there is no correction.
I used two different mount points from rtk2go.com both in Austria, one is only 3 km away the other abt 180 km. But for both the same issue.

When I look at "monitor" at "station info" then I see for base station the position but not for rover.

Do you have any ideas where I can tune this system ?

Did you also see my remark above the fact that mount point options are not correctly displayed and saved ?

Kind regards
Hans

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