RS2 measures wrong ellipsoidal height

Firmware v2.23.9 and ReachView 3 v4.11 Beta.
I tried different apps: RS2 Web interface, Reachview 3 and FieldGenius for Android.
Used different NTRIP Casters: BKG IGS-IP.net and SAPOS M-V as VRS.

I am a civil engineer and recently purchased my first RS2.
Soon we had a project where we had to measuring some manhole cover on the streets. These where covered by a official surveying plan with “official” heights.
Surprisingly they differ from the with the RS2 measured ones. All measured values differed about 0.8 metres. First i thougt about a mistake. But a colleague which is a graduated surveyor suffers the same experience at another project. Also there the differences where about 0.8 metres.
We spoke an brainstormed about getting a solution and checked every setting twice. But no solution.
Luckily we have a official survey point in the center of our town since 2019, where the official ellipsoidal height of this point is written. I decided to just measure this height on the point to exclude all tranformations as a reason for our issue.

The result was not as expected: Also the measured ellipsoidal height on this point differs about 0.8 metres. It should be 53.363 m. I measured 54.160 m.
I did not use a pole, instead i set up the RS2 direkt on the measuring point (considered in the app).

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How can it be? Can it be, that the RS2 is not calibrated some how?
I would be glad, if anybody can help to find a solution how to get the right values!

What is your base?

Base via NTRIP www.igs-ip.net:2101, Mountpoint Warnemünde. ca 10km distance

If you shift all points by 0.8, will all points have the correct heights?

Can you post your raw files? Have you trues post-processing?

Project A
RS2 Plan Difference
Schacht1 19,93 19,13 0,80
Schacht2 19,78 19,05 0,73
Schacht3 19,41 18,63 0,78
Schacht4 19,04 18,23 0,81
Mean: 0,78
I would say yes.

What do you mean with raw files? Export files?
No postprocessing atm.

The .ubx or rinex files, yes

I have nothing recorded. I just can export to csv. If it really helps to solve the problem i can record the files at another journey.
If so, i would be glad, if you point me how to record the files.

If you make another run, it would be quite interesting to have the raw-files.
I think your problem is rooted in that the base coordinates transmitted are not ETRS89. However, those are supplied from i.e. Euref, and can easily be used for post-processing.

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  1. So i shoud do logging in the rover and send it to you? Or need i use another app?
  2. You mean i should do use another caster (like www.euref-ip.net)? I tried SAPOS (ETRS89) too and i think it delivered the same (wrong) data.

It probably just means that your NTRIP caster is sending elevations that are different from what was used during the MH survey. I see a difference in elevations due to different geoid models used in the 2 different surveys. Unless you have more info on how the MH got their elevations, I would just adopt the present MH as correct for your survey purposes.

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@jjb, @Nordstern,

According to the survey control point, geoid separation at this place is 38.38 meters, so the 0.80 cm difference can’t be related to a ellipsoid/normal height error.

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What datum is your NTRIP caster using? This could make the difference.

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1: Log both rover .ubx and the correction stream from your NTRIP provider.

2: Yep, they are essentially the same streams as far as I know.

Do not assume. I thought mine was WGS84 and found out this year it is NAD83 (2011) they also use a different datum for height. Sorry couldn’t find it this AM

That’s why I like to post-process my data. Then I am in complete control.

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I will try to make another survey. Meanwhile some addational data. I use this NTRIP Base:

I have never post processed. Not needed in my application. Everything is relevant to the the base and the survey I do on a job site.

I found the difference in datum when checking the RS2 for accuracy. I am using the Ohio CORS network for correction, found a local survey point and did a 15 minute average. X/Y came out extremely close, Z was off some. When researching I found the different datums. Never did post process to see what it came up with. Thought about it but, I am in my busy season and time is very limited right now. Good winter project.

http://www.epncb.oma.be/_productsservices/coordinates/crd4station.php?station=WARN00DEU

Have used the same station before. Here is a list station coordinates, including ETRS89