UBX_Integrity_Checker : incorrect error detection

[Eric-FR]

UBX_Integrity_Checker is reporting a lot of errors on my ubx log files recorded since 21/12/17.

Sparkfun RTK Express with RTK_Surveyor_Firmware_v110-RCDec-13.zip. Logging on the µSD card.

Static recording with or without RTK correction.

UBX_Integrity_Checker is complaining about:
Panic!! Excessive NMEA message length!

Sample log (without RTK correction):
SFE_Express_211221_122914.zip

No problem with ubx_convert, u-center or rtklib (RTKPlot and RTKConv).

RTK Express settings:
SFE_Express_Settings.txt

[Eric-FR]

With ubx_convert:

[PaulZC]

Hi @Eric-FR ,

Thank you for reporting this.

The code was using a maximum NMEA length ( max_nmea_len ) of 100 characters:

SparkFun_u-blox_GNSS_Arduino_Library/Utils/UBX_Integrity_Checker.py

Line 149 in 0b298e7

max_nmea_len = 100 # Maximum length for an NMEA message: use this to detect if we have lost sync while receiving an NMEA message

But, from your data, I can see that the PUBX (u-blox proprietary NMEA messages) can exceed that.

I have updated the tool: I have increased the maximum length to 128; and also record the longest NMEA message length.

Enjoy!
Paul

[Eric-FR]

Do you have any reason to believe that NMEA sentences length will not be higher than 128?
I just found one with 116 characters:

$PUBX,00,122623.00,4511.08102,N,00544.93346,E,264.521,D3,0.014,0.012,0.013,0.00,-0.006,1.0,0.58,0.86,0.60,25,0,0*55

[PaulZC]

128 is just an "educated guess"!

If you see PUBX messages longer than this, please let me know. Thanks!

[Eric-FR]

Although I can't find the official source of NMEA standard (that may not be freely available), it is commonly stated like in wikipedia that:

Messages have a maximum length of 82 characters, including the $ or ! starting character and the ending

So, PUBX don't comply with NMEA standard, isn't it?

Should we have a soft warning for sentences exceeding 82 characters and stronger action over a higher limit like 128 characters?

[Eric-FR]

I just found classical sentences exceeding the official limit:

$GNGGA,185118.00,4533.5955918,N,00555.8326327,E,4,12,0.68,316.817,M,47.337,M,1.0,0000*6E

[nseidle]

Is that with high precision turned on?