Vertical datum transformation

Emlid Flow & Emlid Flow 360
1

Hi,

I can’t find the right converter for the vertical datum.

I used the HBG18 converter for Belgium as shown on the Emlid website.

Yet I get a difference of about 5 meters from the second leveling used in Belgium. I attach 2 screenshots to show you better the situation.

Screenshot_20220128_094303_com.emlid.reachview3|256x550

Screenshot_20220128_094253_com.android.chrome
Screenshot_20220128_094253_com.android.chrome1080×2312 443 KB

3

Hi Fabian,

Welcome to our community forum!

Do you work with NTRIP service or with your own base? If you work with your base, do you enter coordinates manually or average them?

4

Hi Kirill

I work with NTRIP.

Thanks for your help!

5

Does it say when the point was last measured from the state?

6

There were no point, I’ve created it with two reach rs+ with NTRIP correction. I’ve made the measure in average fix mode.

1 Like
7

How did you verify that the point is solid coming from the RS+?

8

I had solid green for the base and the rover. I was not in the best condition but I’ve measured the point in the mode fix only and during 11 sec.

I’ve taken a look on an official map to compare roughly the values but I didn’t expected so much difference.

Screenshot_20220128_185912_com.emlid.reachview3|256x550

9

So if I understand correctly, you made the following connections:

  • Connected ntrip to your base RS+
  • Configured the RS+ to be in base mode using average fix?
  • Using Lora? you made a connection to your Base RS+ from your Rover RS+?
  • You measured the point for 11 seconds for 11 seconds
10
  • Connected ntrip to your base RS+. yes
  • Configured the RS+ to be in base mode using average fix? Yes
  • Using Lora? Yes. you made a connection to your Base RS+ from your Rover RS+? Yes
  • You measured the point for 11 seconds. yes with the mode collect the point only with a fix.
11

Looking at the environment of your coordinate, I would think that 11 seconds is on the low side using a single frequency receiver like the RS+. However, that shouldn’t account for 5 meter difference.

But, these errors are usually caused by user-error, if the receiver was fixed. Things like pole-heights etc.

12

Hi Fabian,

I’ve taken a look on an official map to compare roughly the values but I didn’t expected so much difference.

As I see from your screenshot, you averaged the base position via NTRIP. Then you checked it and noticed the difference. What is the official map you used for comparison? Could you share the source with those known points?

13

The official map is called wallOnMap

https://geoportail.wallonie.be/files/GeoViewer/Main/index.html#BBOX=148914.91069250763,149867.41259751143,171581.03461592138,173292.89220630325

It give the coordinates any ware in the French part in Belgium. They said that the accuracy is about 12 cm.

14

Fabian,

According to your description, you did everything right, and Reach calculates the solution correctly. I see no obvious reasons not to trust this solution.

As I got, this map doesn’t provide a list of benchmarks with precise coordinates. So, we can only compare Reach coordinates with coordinates of a pointer. This is a too rough way to draw any conclusions.

Also, I couldn’t find which vertical datum this map is based on. It could be a reason for vertical mismatch as well.

However, if you still have doubts, you can check Reach on a benchmark with known coordinates. And I’m ready to help you with that.

1 Like
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