[gdal-dev] Apply Vertical Grid Shift to coordinate

[Matthias Kuhn]

Hi

I am trying to apply a vertical grid shift to a coordinate. I am
extrapolating from the example in the documentation at
https://proj.org/operations/transformations/vgridshift.html

The command I am entering is

echo 46.9480 7.4474 590 2020 | cct +proj=vgridshift
+grids=./geoid+HTRANS_ETRS2020.gtx

the result is:

 46.9480000000    7.4474000000          -inf     2020.0000

I was hoping for the altitude being corrected by roughly 50 meters (instead
of being -inf).

The file geoid+HTRANS_ETRS2020.gtx is located in the current directory and
the coordinates should be within the applicable extent. 2020 was just a
random value (current year), but I guess it should not make any difference.

I guess it's just too late and I am missing something obvious. But if
someone could give me a hint to get me up and running, that would be great.

Thanks in advance
Matthias
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