How to use RTCM data to achieve RTK?

I’m using this example on an ESP32 Thing Plus C with a ZED-F9P and it’s working fine, but it only outputs RTCM data. How do I apply the RTCM data to the GPS data and achieve RTK? My goal is to have the ESP32 Thing Plus C output RTK Latitude and Longitude to the serial monitor.

Example output:

RTCM pushed to ZED: 245

RTCM pushed to ZED: 525

RTCM pushed to ZED: 3678

RTCM pushed to ZED: 3644

Any ideas would be appreciated! Thanks :grin:

Answer from PaulZC on Sparkfun Forum

Hi Jacob,

It sounds like everything is working OK. But, correct, there is nothing in that example to actually print out the position.

Please try Example17. It is better-structured and uses callbacks to: display your position; and push NMEA GGA data to the server. Some NTRIP servers require the GGA data, others don’t. If the GGA data causes problems, you can comment this line to disable the push: … ck.ino#L81

Have fun!

1 Like

Hi Jacob,

Sorry it took us a while to get to this one! Did you end up resolving your issues with the example code suggested by PaulZC? If you’re still having issues the best thing to do would be to share more about your hardware setup (photos of how you’ve got everything connected) and your code (``` three backticks either side of your code for nice formatting.)

Keen to find out if you got to the bottom of this one, RTK is super cool IMO!

G’day James,

Yes I worked it out. Example 17 allows me to print RTK coordinates. I’m just so new I can’t always tell what the example does before someone tells me :grin:

I put my credentials in the secrets.h file and commented out the bits of the example I didn’t need/want to print like the height measurment and all the text.

Definitely super cool. Exciting to watch the accuracy get down to 14mm :smile:


Hi Jacob.

Just interested. What did you check that against/with.
Cheers Bob

Hey Bob,

Line 138 - 141 prints the horizontal accuracy estimate.

I suppose I have to trust it, although I have calculated it from scratch using this table and a calculator


Hi Jacob
Would be an interesting exercise to see just how close your device is. Could do a comparison if you can find a survey trig point. There is one not far from where I live in the shallows of a lake. Consists of a concrete slap on a rock shelf with a concrete column of about 1M high on it. On top is a brass plaque with what is supposed to be the correct lat and long of the point marked in the centre of the plaque. One day when I get to it I am going down to see just how close my SatNav and phone GPS is. I think the SatNav claims within 6M.
Cheers Bob

I’ve used the Google Maps API to display maps in u-center, which gives a very reliable real-time map centred on your location. Also, you can click (or maybe right click?) any point on google maps and get the exact coordinates of that point. You might be able to compare your module’s output to any visible landmark, like the corner of a driveway.