Hi,
Yesterday I figured out what was wrong with APM plus RTK. After several attempts I realized that the M8N installed on Navio+ can handle TRK-MEAS TRK-SFRBX message for RTK only at 1Hz. This is also mentioned here http://community.emlid.com/t/connect-u-blox-neo-6t-usb-to-ethernet by @mikhail.avkhimenia . APM sets gps rate at 5Hz by default of course and that’s the source of wrong ground speed described above.
There is a thread here RTKLIB-Anwendungen mit u-blox M8 - Seite 2 - Geospector GPS-Forum (vormals kowoma GPS-Forum) says M8N is capable to handle raw messages at 5Hz (even 10Hz) disabling glonass and SBAS.
How can I do it after the initializiation made by APM’s gps driver? Should I change the driver and compile it again or I can disable glonass and SBAS by injecting command with u-center or something else.
Actually I know that it would be more simple if I connect a new receiver on the usb but the use of M8N on the Navio+ is more elegant and compact. (BTW when will be available a new usb dongle on the store?)