Base station with fix coordinates – which coordinate system ETRS, Global CS or what?

Q&A forumCategory: QuestionsBase station with fix coordinates – which coordinate system ETRS, Global CS or what?
forum asked 2 months ago
I got an offical ETRS89 reference point not far away my base station.
I went there with my rover and measured the position and going to correct now the my base station fix position by the delta between what my rover got and what officially is known about this reference point.
However, u-blox u-center just asks for Lat Long and Alt. What coordinate system is required by default and can I configure this? Also the major difference seems to be in height (which version I use and this can vary dramatically…)….
Thanks for hints!

4 Answers
Ardusimple Staff answered 2 months ago
Hi forum,
ZED-F9P doesn’t need to know which coordinate system you are setting, if you set your base station parameters in ETRS89, you rover will provide positions in ETRS89.

forum answered 2 months ago
Danke für die Antwort, das kann ich nun nicht nachvollziehen. Wenn er sich im Surey-In befindet, ist mir klar, dass die Basis sich selber einmisst, aber wenn ich extern die Koordinaten eingebe….
Ist mein Verständnis falsch, dass die unterschiedlichen Koordinatensystem voneinander (leicht) abweichen? Damit wäre doch aber auch die Ermittlung der Korrekturdaten falsch. Ich benutzte eine Survey-Rover zum vermessen, das heißt die ausgegebenen Daten müssen absolut richtig sein, nicht nur relativ.

Ardusimple Staff answered 2 months ago
Yes each coordinate system differs from each other, sometimes more than 1 meter offset.
If you let a base station self-calibrate, it will do it in WGS84, but in a self calibration you will always have 1-2 meters error (this is the GNSS error).
In order to do absolute accurate measurements in your wished coordinate system you must:

  • Install the base station in a known location, or install a temporary base station in a known location within 35km from your point, so you can calculate the position of your base station accurately.
  • A known location, should provide you location but also which coordinate system is using, and in this case this is the coordinate system your rover will use.
  • Alternatively you can also use a very short subscription to a correction service to calibrate your base station.

You can read more about this topic in:

forum answered 2 months ago
Thanks for the answer, but yes I understood all those aspects you are mentioned very well, and yes I also got advised how to measure the “exact” position (in my case with the offical reference points and their official coordinates from authorities), and I know now the numbers of my coordinates in ETRS89. 
But coming back to my basic question:
I do not see the possibilites to specifiy the coordinate system in my base station configuration. So when I enter the numbers in u-center, what is the coordiante system for? Or is there a possiblity to specify it? Or do I need to calculate from ETRS89 to a different one (WGS?) and enter then those coordinates into the base station? 
Staff replied 1 month ago

A base rover-setup doesn’t need to know the coordinates, because they work on a “relative location” setup. If you use a specific set of latitude, longitude, altitude in a specific coordinate system, the rover will be working on this exact same coordinate system.

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