Issues with Coordinate Transformation from WGS84 - ETRS89 - DBREF in Metashape

[Photo]

Hello everyone,

I conducted a survey using an RTK drone and laid out GCPs, which I measured using GNSS antenna in the DBREF coordinate system. I am trying to transform the coordinates of the images from WGS84 to DBREF in Metashape, but unfortunately, this is not supported. In this case, I am forced to first transform my WGS84 coordinates to ETRS89 and then from ETRS89 to DBREF. I do not have transformation parameters from WGS84 to DBREF, but I do have them from ETRS89 to DBREF. There is always an issue with the elevation; the horizontal position seems to be somewhat accurate, and it is corrected when the elevation is correct. The transformation in Metashape from WGS84 to ETRS89 should be seamless, but unfortunately, the elevation is incorrect here - I would say that the geoid undulation is not subtracted. Has anyone encountered this issue before, and how can I deal with it? Thank you in advance.

Best regards
Photo

[Paulo]

Hello Photo,

I suppose that the DB_REF datum is based on a different ellipsoid and is not geocentric and thus you have a 7 parameter transformation between ETRS89 and DB_REF, Since WGS84 and ETRS89 are equivalent you can apply the same transformation for WGS84 to DB_REF ....

As for elevation, to take into account geoid you need to use a Compound transformation including a geoid file for Vertical datum see following https://agisoft.freshdesk.com/support/solutions/articles/31000148332-how-to-use-height-above-geoid-for-the-coordinate-system

To set up the 7 parameter transformation for CS DB_REF see following  attachment ....

Hope this helps,

[Photo]

Hello Paul Pelletier,
thank you very much for your support. I have ordered the appropriate geoid and will give it a try. And thanks again for the information that I can directly transform from WGS84 to DBREF, I find it great as it saves a step.

Best regards
Photo

[Paulo]

photo,

great to hear! Now if your ordered geoid is referenced to ETRS89 datum (i.e. geoid height refers to geocentric ETRS89 datum) and want to use a geoid file referenced to non-geocentric DBREF datum, you must follow following to create relevant geoid for DBREF.....https://agisoft.freshdesk.com/support/solutions/articles/31000161533-what-to-do-if-you-need-to-use-an-existing-geoid-on-another-datum

[Photo]

Hello Paulo,

I just received the data, but unfortunately, it's available in the following formats:
ASCII, binary, Javad, for Leica, Survey, Topcon, and Trimble.

I've tried multiple times to import it as shown here: https://agisoft.freshdesk.com/support/solutions/articles/31000148332-how-to-use-height-above-geoid-for-the-coordinate-system
However, it doesn't work or sometimes displays an "out of range" error. I've tried numerous times, but with no success.

Is there any way to convert these formats? Or do I absolutely require the geoid in TIF format? I greatly appreciate your support.

Best regards
Photo

[Paulo]

Helo photo,

it should work in Ascii where each record is in the form of lat,long,Geoid height or long,lat,geoid height.... Also Trimble ggf format file....

If your geoid is the BKG Quasigeoid of the Federal Republic of Germany GCG2016. Then you can use ascii format as:

Code: [Select]

5.1 ASCII format
The ASCII file contains one dataset per raster point consisting of the point position coordinates (in degrees) and the pertaining quasigeoid height (in m). The columns are separated by a blank space. As file extension “.txt“ is used.
As pseudovalue outside the territory of the FRG for the quasigeoid height the value “999999.“ has been entered.
Example:
53.64583333 13.86875 36.4582
53.64583333 13.88125 36.4363
...Then use Table lat/lon/alt (*.txt) when adding your geoid file as in following screen shot...