I have a NEO-M8P attached to a u-blox antenna. If I run the Datalogging example3 (or any other) to export RXM SFRBX RAWX the data seems correct but the time has just question marks:
I am using I2C with an Adafruit Adalogger but I don’t see how that would impact the time. I am powering the NEO-M8P with a different USB cable but not transferring data, only power. I don’t see a difference in the library for exporting this versus NMEA sentences where the time is correctly outputted.
Any suggestion for the cause or solution is appreciated.
The Datalogging Example3 does not log the time directly. So I think you must be using u-center to view the data - and it is u-center that is generating the question marks?
I think this is probably because you are not logging any messages that contain the time. Try adding PVT (Position Velocity Time). Example1 shows how to do this. u-center should then be able to extract the time…
When you connect direct to USB, u-center will extract the time from the standard NMEA messages. Example3 disables NMEA on I2C.
Thanks, Paul. It had not occurred to me but maybe I do not need those time signatures to convert to an OBS and then submit for PPP. Do you know if those are necessary? If not, I will submit a file to see if it works and it doesn’t will add the PVT time next try.
PVT isn’t necessary for PPP. For PPP, the time is derived from the satellite data itself in SFRBX, correlated with the Time-Of-Week in RAWX. PVT would only help with your data display in u-center.
Thanks again, Paul. I still don’t understand the many variables and neither the u-center manual nor the RtKlib manual are very helpful. My RXM-SFRBX_RAWX file does not convert to an OBS file using RTKlib like it does when I send to u-center. Do I need to add the receiver header to the file for RTKlib to process it? That is the only other thing I see that is different although hard to be sure with ascii characters.
I haven’t tried processing SFRBX and RAWX into an OBS file for a while. But, when I’ve done it previously, it has “just worked”… I know this doesn’t help much. Please make sure you are using Tim Everett’s fork of RTKLIB. He has made several changes to better support u-blox UBX data.
UBX-RXM-RAWX should have ToW and Week Number data on each message, it should be enough to generate RINEX observation files. You can pull navigation files and precise ephemeris directly from the NOAA CORS Servers, so not really necessary to capture via UBX-RXM-SFRBX.
Adding UBX-NAV-PVT would allow for an estimated position to be added to the RINEX OBS headers.
+1 on using RTK Explorer fork.
Now, most probably, your issue is with data corruption. If the packets are not intact the tools will just ignore the content. The output files or .UBX should be loadable in uCenter Classic for play back and review.
For a problem file, perhaps PM me with a problem file, and I’ll do an integrity check.
Thanks Clive… I tried to PM you with a small UBX file but does not appear to be downloading. I had to convert it to a pdf to attach so I must be doing something wrong. The time stamp is the only difference I see in u-center between Paul’s Sparkfun library and u-center so I will work on that. Let me know if the PM does come through.