Coordinate transformations with pipelines

[Antonio Valanzano]

I am usign PostGIS 3.5 with PostgreSQL 17.0

Here are the details for my installation:

"postgis_full_version"
"POSTGIS=""3.5.3 3.5.3"" [EXTENSION] PGSQL=""170""
GEOS=""3.13.1-CAPI-1.19.2"" PROJ=""8.2.1 NETWORK_ENABLED=OFF
URL_ENDPOINT=https://cdn.proj.org
USER_WRITABLE_DIRECTORY=C:\Windows\ServiceProfiles\NetworkService\AppData\Local/proj

DATABASE_PATH=C:\Program
Files\PostgreSQL\17\share\contrib\postgis-3.5\proj\proj.db"" (compiled
against PROJ 8.2.1)
LIBXML=""2.12.5"" LIBJSON=""0.12"" LIBPROTOBUF=""1.2.1"" WAGYU=""0.5.0
(Internal)"" (core procs from ""3.5.2 3.5.2"" need upgrade)"


I have done the following coordinate transformation
from  ED50 / UTM zone 33N  (espg:23033)
to  ETRS89 / UTM zone 33N  (epsg:25833

SELECT
  ST_X(ST_Transform(ST_Point(541000,4516000,23033),25833)) as X,
  ST_Y(ST_Transform(ST_Point(541000,4516000,23033),25833)) as Y;

-- result
"x" "y"
540998.1383329581 4515921.565374701

I have read that the best way to utilize PROJ.6 capabilities is by allowing
the library to freely choose the best possible transformation paths
between the origin and the destination CRSes.

Does someone know how to find which specific transformation pipeline has
been chosen by the PROJ.6 library in this specific transformation ?

Antonio
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