Convert ubx files to rinex

Q&A forumConvert ubx files to rinex
ALBERTO FALAVIGNA asked 2 weeks ago
Hello,
I tried to convert an ubx file (saved by SWMAP in its RAWDATA folder) to rinex with RTKconv but the conversion does not take place!
The ubx files saved by swmap contain observable position and navigation data and are they convertible to rinex?
I thank you all !
alberto
5 Answers
clive1 answered 2 weeks ago

Observation files would need UBX-RXM-RAWX messages, Navigation files would need UBX-RXM-SFRBX messages

ALBERTO FALAVIGNA answered 2 weeks ago

OK thank you very much clive1!
But are these messages also available on uart2 (bluethoot link)? 

Greetings and thanks again for your interest!
clive1 replied 2 weeks ago

No, UART2 cannot output UBX messages.

It can output RTCM3, but you’d need to use RTCM3 to RINEX conversion software for those.

vvlachak replied 1 week ago

Hello clive1,
As far as I know RTCM3 contains/transmits correction information from base to rover. How it is possible to reconstruct the raw observation from the RTCM3 data? (I know is a fundamental question). Is this also possible with NMEA that in principle also carries correction data? Are the observations reconstructed from RTCM3 at the same quality as the raw observations? Thanks in advance.

clive1 replied 1 week ago

MSM message are NOT CORRECTIONS, in fact most of the carrier phase based messages from RTCM2 and RTCM3 are of observations so the receiver (rover) can solve for both locations and the separation between them. ie a Geometry problem, best fitting a dozen or so triangles sharing a common baseline.
Carrier measurements are hugely dependent on the local clock references in each receiver.
Pseudo-Range corrections (DGPS) were a thing, especially when the measurements were subject to large amounts of SA dither. In modern times the accuracy improvement provided here was in the order of 50-100 cm.ie shrinking a 3m CEP to a 2.5m CEP
Back when I analyzed MSM4 vs MSM7 the difference in solution was fractions of a mm

clive1 replied 1 week ago

It shouldn’t be that hard to generate UBX based RINEX files, and RTCM3 ones, from contemporary data, and post-process those against your local CORS, or in a self-relative sense. In the latter presumably observing an RMS convergence number approaching zero.

vvlachak replied 1 week ago

Thanks a lot for this reply but also for the knowledge you share here and elsewhere.
I am going to do the test you proposed.
It seems that I had a confusion concerning RTCM messages. I thought that the base sends corrections for the systematic, to be directly applied to the rover observations.
Thanks once again, I hope to “meet” you again at the next interesting post ūüôā

clive1 replied 1 week ago

Thanks
It is not helped by people generally referring to them as “corrections”, which is only true of “differential” methods that attempt to remove the most simple common-mode error. ie position/clock error of the satellite, and atmospheric conditions encountered in transit.
RTK generally requires that you solve the local time errors, on a continuous time line (clock performance epoch to epoch can be tracked), error in the local clock impacts the perceived frequency of the carrier, how it advances, and distorts the doppler. The receiver (rover) also needs to pull the measurements/observations to a common instance, using interpolation/extrapolation, so all the moving parts in the system are frozen in a given instance.

ALBERTO FALAVIGNA answered 2 weeks ago

OK thank you very much clive1!
But are these messages also available on uart2 (bluethoot link)? 

Greetings and thanks again for your interest!
ALBERTO FALAVIGNA answered 2 weeks ago
Thanks clive1 for assistance! SWmaps, when the mobile is connected via bluethoot, it stores a "fake" ubx !? (without location and navigation data).
With which smartphone app then do I store raw data from uart2 in rtcm3 format to be subsequently converted to rinex?
Or do I solve as did the friend Mauro who soldered the bluthoot card on uart1?
Greetings and good and fresh day!
clive1 replied 2 weeks ago

Yes, this really isn’t my software.
The .UBX suffix doesn’t describe the file content, uBlox stores all serial port traffic to such files, be it UBX, NMEA or RTCM3. What SWmaps does is on them, I’m not using this software, and I’m not familiar with its source code, or features/function.
The ZED can output NMEA+RTCM3 on UART2, if the software you use can record what comes out of the receiver, you’ll be able to use it.
To capture UBX messages you’ll need some connectivity to UART1, a connection via BlueTooth would no doubt suffice.

ALBERTO FALAVIGNA answered 2 weeks ago
Ok clive1: all very clear and useful.
Many greetings and thanks!