A few days ago, I found out a difference in the transformed coordinates derived from Emlid Flow and an official software that we use in Greece.
In my projects I use GGRS87 / HEPOS + Greece GREEKGEOID2010 height
I used the origin coordinates (long, lat, ellipHeight) in HTRS87 and transformed them to GGRS87 using the Hepos Transformation Tool. In Easting and Northing, the differences are in mm. In Elevation is sometimes 20 cm (probably problem with Geoid used).
This has nothing to do with accuracies of the gnss antenna. It has to do with the transformation that is used and the Geoid.
My question is which conversion is correct?
Did you get that GREEKGEOID2010 from a valid source (because I have never seen it before)?
I don’t know which conversion is right or wrong.
I am uploading an Excel file with the differences, and I am posting 2 Links to download the Software and to download the geoid files.
The geoid in HEPOS transformation tool and the geoid in Emlid Flow are different. Emlid supports GREEKGEOID2010, a gravimetric geoid model based on the remove-compute-restore technique with EGM2008 being used as a reference field. You can read more about the geoid model here.
Meanwhile, the one used in HEPOS transformation tool is a geometric geoid model developed and computed by Ktimatologio S.A. I came across this article from Ktimatologio S.A, and I’m quoting this:
In order to cover the needs of HEPOS users to estimate orthometric heights, KTIMATOLOGIO S.A. developed a geoid model to be used with HEPOS. This geoid has been computed based solely on geometric information, i.e. ellipsoidal heights obtained by GPS at points with known orthometric heights.
To answer your question, neither of the heights are wrong. It’s just that the two systems are using different geoid models resulting in different height computation.
Since in Greece we use the Geoid from the Hepos transformation tool, I believe that you should include it in the available Geoids for Greece or give us the option to use custom Geoids.
Do you believe such things is possible?
We don’t want to use 3rd party apps to be able to export the “idial” heights.
I see. At the moment we don’t support the upload of custom geoid models. But I’ve noted this as a feature request, along with support for geoid from HEPOS in Emlid Flow. For now, I suggest downloading the CSV file from Emlid Flow and transforming those points in HEPOS if GREEKGEOID2010 doesn’t meet your needs.
I’ll keep you posted as soon as we have updates on your requests!
