NMEA $GNGGA sentence output (reference station ID)

GPS/GNSS Development Boards
1

I use some python code that modifies a $GNGGA sentence and converts it into a multi vehicle $GID sentence using the reference station ID field as a unique identifier for each asset tracked.

When I tested this with an Express and Facet I realised this field is already being output with a unique ID (which is fantastic news), but I did wonder how exactly this is being created? Below are two examples (one of each) with ID’s of 0123 & 0136.

$GNGGA,094851.00,5109.3453148,N,00050.5181079,E,2,12,0.72,58.136,M,45.492,M,0123*76

$GNGGA,094837.00,5109.3453191,N,00050.5172778,E,2,12,0.63,56.994,M,45.492,M,0136*72

2

Hi,

That ID is:

14 diffStation numeric - - ID of station providing differential corrections (null when DGPS is not used)

So I’m guessing it is extracted from the RTCM messages from your correction source. Where’s your RTCM coming from?

Just FYI, the next version of the firmware has the ability to record the coordinates of the RTCM Antenna Reference Point - extracted from the RTCM 1005 or 1006 data. We copy it into a custom GNTXT message which can be enabled for logging.

But I guess what you really want is ether the ESP32 MAC Address - which is unique - and/or the ZED-F9P serial number - also unique. I’m pretty sure we already log the MAC Address. Certainly it is available via the menus. But we don’t currently log the UBX-SEC-UNIQID serial number. Should be easy enough to add though. I’ll open an issue for it.

Cheers,

Paul

3

Hi Paul,

That’s just the thing… I’m not using any RTCM correction source at all so I’m bemused at what is being populated to that field by default, which you stated should be null…

Cheers,

Mark

4

Hi Mark,

I think I’m right in saying that we don’t manipulate the GGA message contents and that that field must be coming directly from the GNSS module. If you’re not applying corrections then, right now, I’m equally puzzled about where it is coming from… Maybe it is an SBAS thing?

Just FYI, I got the GNSS unique ID code running over the weekend. The unique ID will be added to the start of each log file, from the next release. GNTXT,01,01,11 contains the GNSS unique ID. GNTXT,01,01,07 contains four digits from the ESP32’s MAC Address. Those two together will uniquely identify the unit. Please see:

https://github.com/sparkfun/SparkFun_RT … 1567346348

Best wishes,

Paul

5

Ah. OK. You’re in the UK too… Yeah, It is an EGNOS (SBAS) thing. It is the EGNOS satellite identifier: 120, 123, and 136.

Best,

Paul

6

Hi Paul, thanks for that. I had literally just fired up u-center to check and the penny dropped… still odd that with the two receivers next to each use different satellites!

Cheers,

Mark