Set CRS Epoch in Emlid Flow for Reach RS2+

My Reach RS2+ is setup as a Rover and connected to an NTRIP-Caster provided by the German SAPOS service. When setting the coordinate reference system (CRS) for a new project, there seems to be no option to set the epoch. SAPOS operates with ETRS89, and since this CRS is dynamic due to the continental shift of the Eurasian Plate, it seems to be crucial to have the correct epoch selected ( Does emlid flow provide this option and I missed it?

Since SAPOS stations are drifting together with the continental plate, there is no need to specify the epoch. It’s only required when the correction source is in ITRF.


Thanks for your fast reply. So this means with SAPOS the epoch is inherently set to the time of measurement, got it!

Maybe you have a clue about another CRS problem that I’m currently struggling with: I measured the same point with different project CRS settings: First time with WGS84 and second time with ETRS89. During each measurement my RS2+ was set up as a rover and connected to the SAPOS NTRIP-Caster. I expected the coordinates of the different CRS to be about 75 cm apart, due to the drift of the ETRS89 system since 1989. However, the coordinates measured in both CRS were almost exactly the same. So what am I missing? Does the RS2+ not support coordinate transformation when connected to an NTRIP-Caster or what is going on?
Thanks for your reply in advance!

The correction stream doesn’t contain information about the source datum, so the app has no way of converting that automatically. When you are selecting a geographic system in Emlid Flow such as ETRS89 the app doesn’t perform any transformation, as it isn’t clear what to transform from. So it is expected that WGS84 and ETRS89 project settings will get you the same position.

This is annoying from the system engineering perspective, but rarely causes difficulties in real life applications. For land survey, most base stations will be tied to the current datum and the app will just perform the projection. This obviously depends on where you are and steps might as well include grid shifts and vertical shifts using geoid models.

What is your end goal? Judging from you using SAPOS you must be in Germany, where we have a well tested implementation of GCG with DHHN height conversion licensed from BKG. This relies on the base station being in ETRS89.

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Thanks for your reply!

My scenario is the following: I received coordinates from a colleague who measured without SAPOS. They measured their points with a RTK-Rover that was linked to a local RTK-Base and set the CRS to WGS84.
Now, I want to stake out these points. For that, I’m using RS2+ as an RTK-Rover linked to the SAPOS-NTRIP-Caster. My initial ideas was to simply import my colleagues’ point coordinates as a shapefile with the CRS set to WGS84. I was hoping that the Emlid Flow Software would transform my colleagues’ WGS84-coordinates to ETRS89 on-the-fly. But this won’t work, right?

So now, based on your information, I have to do the coordinate transformation WGS84 → ETRS89 (with epoch set to 2023) before importing them to Emlid Flow, correct?

Before I can suggest anything, could you please help clarify:
How did you colleague establish the base position when making the measurements? Was the base station placed on some benchmark?
Are any of points in the project physically marked on the ground? If they are, you can try to determine the shift with Localization.

Unfortunately there is nothing more ambiguous in the survey world than WGS84 :smiling_face_with_tear:

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I really appreciate your help. Honestly, I don’t know all the details of my colleague’s measurement. They certainly didn’t place the station on a benchmark, as there is no benchmark close-by to the measurement points.
Concerning physically marked points on the ground: Unfortunately, no, they didn’t mark up any points on the ground. :smiling_face_with_tear:
I will ask my colleagues how they established base position, my guess is by averaging the base station position. I will come back to you and reply later next week, thx again!

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