How RTK correction is ETRS89

Hi there,

we use the RS+ with the Austrian APOS RTK.
My question is more on the technical side. The APOS system sends the correction data in ETRS89 is this then transformed internaly to WGS84, and is the RS+ sending position data in in WGS84 to the provider via VRS? So where happens the coordinate-transformation? Internally? How does this work?
Lately we had some problems to get the right x,y,z - coordinates on the RS+ regardless of the RTK-data mainly the the height is between 40 and 48 m to high. The service man said it is maybe a problem of the modulation of the Geoid and I have to set the right modulation on the machine. But there is no option in ReachView, if needed at all?

Thanks to everyone how can explain some of these questions.



Nop, stays in ETRS89

Doesn’t matter as the need for precision here isn’t critical.

The only conversion that happens is probably from ECEF to Decimal. As the base coordinates are in ETRS89,and the RS+ doesn’t know better, it stays in ETRS89.

This sounds very much like the provider is sending corrections in the local geoid, and not in the global elipsoid. Reach units expects elipsoid.


but how much is the difference between WGS84 and ETRS89 in the xy position? Is it possible to set local Geoid in the RS+?

Our plan was/is to set fix-points on the excavation to use it with a Leica Trs for the everyday use (and some other stuff too). And we need the correct height for the documentation.

Thanks in advance.

You don’t have to care about that, if your base is in ETRS89, your results will be ETRS89 regardless.

You can use ReachView 3 (in beta) for getting the right geoid height, but I still think that the Emlid Receivers are expecting elipsoid from the NTRIP.


Okay thanks.
I have seen that provider has an GIS-grid correction this will maybe help for the xy.
Hmm so we have to find a solution for the correct height.


Hi Marco,

I want to confirm Christian’s words. If the base’s coordinates are in ETRS89, the receiver will send its position to VRS in ETRS89. Also, you’ll get positions in ETRS89 on the rover. There will be no errors or shifts because WGS84 and ETRS89 are so close to each other, and the same calculation methods can be applied to them.

However, if your provider uses some local grid and geoid, it may cause errors in coordinates.

Hey thanks,
yep maybe this causes my problems.
And I will try the ReachView 3 app.

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