[Qgis-user] Integrate custom transformation to Proj Database for use in QGIS

[Andrea Giudiceandrea]

> Klaus Mithöfer mithoefer at gbd-consult.de
> Tue Apr 28 09:43:56 PDT 2026
> i use proj 9.4.0. I want to add a transformation similar to an existing 
> one (code 15984 EPSG 32467 to 258322). But I want to use a different 
> Transformation grid.
> Proj.db has a table grid_transformation. I have added a data set similar 
> to 15984 to code 15984 but with a different grid name.

You probably meant "code 15948 EPSG 31467 to 25832".

For PROJ 9.4, you also need to modify the "usage" table, other then the 
"grid_transformation" table, adding a row corresponding with the row 
added in the "grid_transformation" table.

For example, the following SQL statements add the needed rows for a NTv2 
transformation similar to EPSG:15948 but using the BETA2007_CUSTOM.gsb 
grid shift file:

INSERT INTO "grid_transformation"
VALUES ('PROJ', 'DHDN_TO_ETRS89_CUSTOM', 'DHDN to ETRS89 (CUSTOM)', 
NULL, 'EPSG', '9615', 'NTv2', 'EPSG', '4314', 'EPSG', '4258', '0.9', 
'EPSG', '8656', 'Latitude and longitude difference file', 
'BETA2007_CUSTOM.gsb', NULL, NULL, NULL, NULL, NULL, NULL, NULL, '0');

INSERT INTO "usage"
VALUES (NULL, NULL, 'grid_transformation', 'PROJ', 
'DHDN_TO_ETRS89_CUSTOM', 'EPSG', '3339', 'EPSG', '1041');

Regards.

Andrea