Base station fixed position – how to set high precision coordinates

Q&A forumBase station fixed position – how to set high precision coordinates
steffendring asked 3 months ago

Hallo and a happy new year!
Is it possible to send fixed surveyed coordinates via the NTRIP Master server to RTK2GO?
I cannot find one resp. two fields for entering such coordinates like for example here http://esprtk.wap.sh/tt/tt_d_ntrip_master.html
And how Do I have to configure the Wifi NTRIP Master to work in BOTH the NTRIP server (to RTK2Go) and the NTRIP client mode AT THE SAME TIME?
I tried the whole day to get it work but when I activate the NTRIP server the client doesn´t receive any NTRIP correction signals anymore – thus without the server active receiving correction signals is no problem for the NTRIP client!?
Thank´s and best regards!
Steffen

3 Answers
AndrewRL answered 2 months ago

1. If you are using the Ardusimple wifi NTRIP master then you need a wired connection to U-Centre to change the survey mode to “fixed” and to enter these surveyed coordinates (you need the surveyed height too). You cannot do it over the air. The Esprtk software which you linked is different and includes some U-Centre features.
Since you are using rtk2go you can check the status page for your mountpoint to see the “Pos-LLH” which it has received to see if it is what you expected.
If you are moving the base in the field between surveyed points at different locations then I think you would need either to set the new location in advance or take a windows laptop with U-Centre to do the setup. 
2. When I bought my board I tested survey-in mode with NTRIP client (connected to a remote rtk2go site) and NTRIP server (connected to my mountpoint) active simultaneously and it did seem to work OK. But like you I opted to enter surveyed coordinates for better repeatability.
Are you sure ticking the server box deactivates the client? You can check in U-Centre what messages are being received and with the latest wifi NTRIP Master software (0.4.4) you can see live on the web config pages the number of bytes sent and received over each interface.
But I am confused why you need both active on the same board? If you are using Simplertk2b in base mode and know and are using its high precision surveyed location, surely using the NTRIP client to feed it with RTCM from some other base has no purpose?
 

steffendring answered 2 months ago

Hello Andrew,
thank´s a lot for your detailed answer!
You are right normally I wouldn´t need to connect both – client and server – at the same time. It was only thought for test purposes with u-center.
But never mind what I really would appreciate now is a little help for setting up the server correctly – sending to rtk2go:
Master

  • Do I have to set something else than – HOST: rtk2go.com + Port: 2101+ my mountpoint name + my provided password
  • User not necessary because of NTRIP Rev1?
  • I shouldn´t need a fix IP address serving to rtk2go, right?

SimpleRTK2B

  • Is the following procedure correct → in u-center → UBX-CFG-TMODE3 → do a 1 – Survey-in → switch to 3 – Fixed Mode with the surveyed coordinates?
  • Alternatively doing a Survey-in with the SimpleRTK2B or another receiver separately and add the coordinates manually in 3 – Fixed Mode?

Perhaps we could write a liitle workflow description because its quite a lot of searching and asking 😉 necessary!? I could write it when I get it right and send it to you for correction!?
Best regards!
Steffen

clive1 replied 2 months ago

UBX-CFG-TMODE3 should automatically transition from SURVEY-IN to FIXED MODE once the criteria are met.
General problem with SURVEY-IN, unaided, is the results are rough and non-repeatable.

>>Perhaps we could write a little workflow description because its quite a lot of searching and asking necessary!?
“Tony Stark was able to build this in a cave…with a box of scraps”

AndrewRL replied 2 months ago

Sorry I misunderstood your requirements. I thought you ALREADY had the high precision surveyed co-ordinates and were simply asking how to enter them.

Yes, what you say about setting up the NTRIP Master is correct, and yes rtk2go.com will work if you don’t have a static IP (and even behind CGNAT).

BUT don’t forget that they will have supplied your Simplertk2b in rover mode. You must load it with the base station .cfg file which Ardusimple provide under the “Support” tab above otherwise you will NOT get any RTCM output.

As @clive1 points out you don’t need to alter the mode, it is all automatic, but with the default settings when surveying stops you could be out by 1m or more. You have already succeeded connecting the XBee’s NTRIP client to a caster and you can get a better start-up location if you can at least get that into float-rtk mode. You will need to enable RTCM input on UART2 (if not already enabled) and adjust the time and precision settings.

If the base is always to be in the same place you do really need to forget about float mode and to enter fixed coordinates so that the rover gets repeatable results.

I got my starting position by operating the base in rover mode after fixing the antenna in a good-sky location but before loading the base .cfg by connecting the XBee Wifi NTRIP master to a distant (100km) base and taking an average of the positions over an hour when it (eventually) temporarily achieved RTK-Fixed mode. I thought that would be quite accurate*.

Unless you want to be consistent with already surveyed points it doesn’t matter if the base position is a little off, but at least your rover positions will be repeatable.

I was fortunate that I had a surveyed point within 2km of my new base, so I put the rover there and read its location, calculated the difference from the professional survey and manually adjusted the location of the base which I had entered in U-Centre by the corresponding amount and it now reads consistently with other professional stuff over a few kms.

*I was surprised that the location I had initially was wrong by as much as 0.5m east and 1.7m north. I was expecting it to be correct to 1cm+1ppm (ie about 0.1m). The base was an official EUREF station calibrated to ETRF2000 and operated by Ordnance Survey (highly reputable) so I don’t know what went wrong (and even if I repeat the exercise now I get the same consistent error). I have the local professional survey results before they applied a local scale factor so that is not it. Maybe the OSTN02 transformation to the local grid is expecting lat-long from a different tectonic plate and compensating needlessly for 30+ years continental drift. But the main purpose is to get the rover to give real-world answers and if it means that the base coordinates have to be faked so be it, but you can’t do that with “survey-in” mode.

steffendring answered 2 months ago

Hello,
thanks for the answers.
#Clive1: Unfortunately aren´t we all “Tonys” 😉 and I think after reading the very detailed answers of Andrew that there is not all obviously regarding the whole process for setting up the new NTRIP Master as server for e.g. rtk2go.
Considering my experiences of researching and teaching students → good instructions spare a lot of the time – in research to look for answers in many different sources like forums and for the masters in the forums to answer the same questions again and again. 
I am working at an university and we want to install a own little base on our roof and incorporate this in our teachings. So defining clear and easy workflows is part of my business 😉
#AndreRL: Thank you very much for your very detailed answer. It is very nice to share your experiences and save other NTRIP Master users s a lot of time. Changing the configurations and the basic settings is no problem because for this Ardusimple has good instructions provided. Only for the NTRIP Master as a server lacks some information. So I will sum up some points which could be added perhaps to the already excellent instruction of https://github.com/nebkat/esp32-xbee/wiki/Getting-Started!?
Best regards!
Steffen