[PROJ] 2D Helmert transformation after the map projection and PROJ won't use added transformation from the database

[Schupp, Leon]

Hello Even,
these are the SQL INSERT statements i used:

INSERT INTO "main"."other_transformation"
("auth_name", "code", "name", "method_auth_name", "method_code", "method_name", "source_crs_auth_name", "source_crs_code", "target_crs_auth_name", "target_crs_code", "accuracy", "deprecated")
VALUES ('PROJ', 'P0001', 'ETRS89 to VVJ', 'PROJ', 'PROJString', '+proj=pipeline
+step +type=proj4 +to=+proj=tmerc +lat_0=0 +lon_0=25 +k=1 +x_0=25500000 +y_0=0 +ellps=GRS80 +units=m +no_defs
+from=+proj=longlat +ellps=WGS84 +units=m +no_defs
+step +proj=helmert +convention=coordinate_frame +x=-6685321.2964 +y=-25439452.96812 +rx=1.00001130081 +ry=-0.00120233218', 'EPSG', '4258', 'EPSG', '36122', 1.0, 0);

INSERT INTO "main"."usage" ("auth_name", "code", "object_table_name", "object_auth_name", "object_code", "extent_auth_name", "extent_code", "scope_auth_name", "scope_code")
VALUES ('PROJ', 'U0002', 'other_transformation', 'PROJ', 'P0001', 'EPSG', '3333', 'EPSG', '1024');


Mit freundlichen Grüßen / Best regards

Leon Schupp
Student - Development Engineer


Von: Even Rouault <even.rouault at spatialys.com>
Gesendet: Donnerstag, 9. September 2021 11:56
An: Schupp, Leon <LSchupp at moba.de>; proj at lists.osgeo.org
Betreff: Re: [PROJ] 2D Helmert transformation after the map projection and PROJ won't use added transformation from the database

Leon,
First question:
Is it possible to add a 2D Helmert transformation to the proj.db database. I tried adding it to the helmert_transformation_table, but proj.db didn't let me choose a projected crs as source transformation.
Yes as designed currently it is limited to source and target CRS being geographic CRS

I want to add a helmert transformation which uses ETRS89/GK25 as source crs and transforms it into the finnish VVJ crs.

My second question is:
I tried adding the helmert transformation as a proj string to the other_transformation table, but proj won't use it. I also added an entry into the usage table for the transformation.
When I add a normal helmert transformation or a grid transformation, proj has no problem using them after they are added, but not when I add a transformation in other_transformation.

Show your SQL INSERT statements
Even

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