HI,
I found the solution.
To make everything work, you also need to write the parameters of the 2 systems 
you want to convert using grid shift (in the epsg_operations.properties file) 
before and after including the gsb file.

This is an example:

3003,3857=CONCAT_MT[INVERSE_MT[PARAM_MT["Transverse_Mercator",\
               PARAMETER["semi_major", 6378388.0],\
               PARAMETER["semi_minor", 6356911.9461279465],\
               PARAMETER["central_meridian", 9.0],\
               PARAMETER["latitude_of_origin", 0.0],\
               PARAMETER["scale_factor", 0.9996],\
               PARAMETER["false_easting", 1500000.0],\
               PARAMETER["false_northing", 0.0]]],\
PARAM_MT["NTv2", PARAMETER["Latitude and longitude difference file", 
"NadRoma40.gsb"]],\
PARAM_MT["Popular Visualisation Pseudo Mercator",\
    PARAMETER["semi_major", 6378137.0],\
    PARAMETER["semi_minor", 6378137.0],\
    PARAMETER["latitude_of_origin", 0.0],\
    PARAMETER["central_meridian", 0.0],\
    PARAMETER["scale_factor", 1.0],\
    PARAMETER["false_easting", 0.0],\
    PARAMETER["false_northing", 0.0]]]

Daniele Maggiolo


Da: Daniele Maggiolo via Geoserver-users <geoserver-users@lists.sourceforge.net>
Inviato: giovedì 2 novembre 2023 14:49
A: geoserver-users@lists.sourceforge.net
Oggetto: [Geoserver-users] Problems adding Grid Shift Transform files

HI,
I tried to configure a grid shift as explained in this guide:

https://docs.geoserver.org/latest/en/user/configuration/crshandling/coordtransforms.html#examples

using a gsb file.

In the epsg_operations.properties file (inside user_projection) I wrote the 
following line:

3857,3003=PARAM_MT["NTv2",PARAMETER["Latitude and longitude difference file", 
"NadRoma40.gsb"]]

and I put the NadRoma40.gsb file inside the same folder (file verified with 
other applications and working correctly).

Now when I try to reproject from 3857 to 3003 if I click on "Show 
transformation details" I see that GeoServer has implemented my configuration 
(it shows me exactly what I wrote in the epsg_operation file), but the 
conversion does not work correctly.
The log tells me "Point (1306188.4848936629, 5743812.429289647) is not covered 
by 'NadRoma40.gsb' NTv2 grid, it will not be moved." but I am sure that the 
point is contained by the grid.

I also tried using the gsd file described in your guide and trying the 
coordinates system in your guide, but nothing with that either.

I'm currently testing everything on a GeoServer version 2.23.1

Daniele Maggiolo
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