[gdal-dev] Transformations with same horizontal datum but different geoid outputs the same Z value

[Diogo]

Hello everyone!

I'm merging multiple elevation datasets from different countries and I
would like to re-project all into the same coordinates system, 4326+3855
using gdalwarp. I'm using `gdaltransform` to confirm that there is in fact
a conversion from the original projection to the aspected one. However, for
some datasets, there is only conversion in the XY axis, while the Z output
is the same as the input.

Below there are some examples (the geoid code is extracted from the dataset
documentation)

Genoa 1942 height (Italy)

$ echo "14.995 37.755 3357" | PROJ_NETWORK=ON gdaltransform --debug on
-s_srs "EPSG:4326+3855" -t_srs "EPSG:32632+5214">> 1028333.73796622
4195591.29690422 3357

N2000 (Finland)

$ echo "25.15296 62.50195 269" | PROJ_NETWORK=ON gdaltransform --debug
on -s_srs "EPSG:4326+3855" -t_srs "EPSG:3067+3900">> 404861.868388335
6931460.32557422 269

EVRF2007 (Estonia)

$ echo "27.059167 57.714444 318" | PROJ_NETWORK=ON gdaltransform
--debug on -s_srs "EPSG:4326+3855" -t_srs "EPSG:3301+5621">>
682284.606829111 6401087.4159131 318


I don't have much experience with the projections and I'm a bit lost
to understand the possible issues, or interpreted the Z output. What
can be the possible issues?

Any help would be appreciated.

Best regards,

Diogo
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