Ntrip for base initial position with data logging

Q&A forumNtrip for base initial position with data logging
Wreck asked 3 years ago
The overall aim I’m trying to achieve is to get cm accurate positions using my f9p rover and a local f9p base, as the nearest CORS I have available is 90km away. 
I have two units, one called ‘Base’ which is set up with an openlog on UART1 which I want to log the RXM-RAWX and RXM-SFRBX stream for post processing a drone GPS against. And on UART2 I want it to transmit RTCM3 corrections via a 900mhz sik radio.
The other unit ‘Rover’ has a bluetooth module on UART1 which I use to connect my android phone to, and UART2 should receive the RTCM3 corrections via the other 900mhz sik radio.
I want to use the ‘rover’ unit initially to connect to a local CORS station 90km away to receive NTRIP corrections to allow me to get a RTK fix and an accurate initial position instead of using the inaccurate survey-in procedure. I then want to set this accurate position into the ‘base’ unit as the tmode fixed position so that it can then output accurate RTCM3 corrections to the rover. It’s also important that the raw stream is logged on UART1 for later post processing. The reason I need to use the rover for this initial position is it is the unit which has the bluetooth module allowing my phone to connect to it and I don’t want to be hauling a laptop around in the field.
I am able to get the ‘rover’ to connect to my android phone via bluetooth on UART1 which runs the lefebure NTRIP client and receives the NTRIP corrections and then gives me a RTK fix and an accurate position.
Problems: How to set this position as the fixed position under tmode on the base, and then get the base to transmit the RTCM3 corrections successfully to the rover. How can I check these messages are being sent or received?
The log stream which should contain the RAWX and SFRBX data to the openlog doesn’t seem to be readable when I try to run it through rtkconv as ublox format.
Not sure what the best way is to show all the relevant config options to troubleshoot both these units?
replied 3 years ago

I’m in the process of setting up a permanent base station so I can’t give definite answers right now until I finish it myself but to answer your first question Section 3.5.7 of the ZED-F9P Integration Manual specifies what CFG items need to be set to set a base station into fixed mode.

replied 3 years ago

As regards your issue with converting from .ubx to RINEX using rtkconv. Does you .ubx file not contain any data or what is happening?

It seems that the current stable release isn’t equipped to handle this data properly. My own experience so far and comments I’ve seen on other forums seem to suggest that rtkconv 2.4.2 will only convert the L1 signals. Tim Everett’s version of RKTLib looks like it will work however. It can be downloaded from here: http://rtkexplorer.com/downloads/rtklib-code/

Here is a screenshot of my .ubx data converted using the main branch stable release v2.4.2 of RTKLib RTKConv vs the same data file converted using the RTKLib Test5 version above. Note how I have both L1 and L2 data when processed using the Test5 program. Also, my E31 and E36 sats are now showing whereas in the main release has a bug (No.141 Unable to handle data of Galileo E31 – E36 satellites) related to these sats so I guess the Test5 version solves this too.


replied 3 years ago

Tim’s been doing a lot of the work, including getting the dual band RXM-RAWX message handled properly. Use his fork of the code.

replied 3 years ago

Thanks for the replies.

I am getting a log from the openlog, but it doesn’t look to be readable in rtkconv so I don’t know what it contains. I have used this same openlog before with an m8n/m8t to record the raw measurements for post processing before and these logs look different. I am using Tim’s demo5 b33b fork of rtklib.

example log: https://drive.google.com/open?id=1DDQObtYzAzyeJ9mTXqLxpCA-YiUHyr0I

I’m wondering if there’s something in my config which is stopping the correct messages from being output to the openlog, so I have attached some screenshots of the generation 9 configuration view showing what’s enabled.

screenshots: https://drive.google.com/open?id=1RNUnwilFBJ4CsEvrmLM6_THPEWDPPObV

replied 3 years ago

Not familiar with the openlog but first thing I’d suggest is trying to log NMEA data if possible to confirm if it logs that correctly/as expected.

Want to learn more about GPS/RTK?

1. Our engineering team will contact you to solve any questions
2. We will keep you updated about promotions and new product releases
3.You will only hear from us when we have important news, we won’t spam your email