[PROJ] National CRS to ITRS

[Lesparre, Jochem]

JL wrote:

> the route trough ETRF2000 should be the default […]



> Thus ETRS89 -> ETRF2000 -> ITRF2000 -> ITRF2014 instead of ETRS89 -> ETRF2014 -> ITRF2014. What makes PROJ choose the latter?



ER wrote:

> PROJ has no idea of what is recommended/preferred by European geodestists ;-) It only trusts records in its database.



> PROJ can only infer pipelines with at most one intermediate CRS. If you want ETRS89 -> ETRF2000 -> ITRF2000 -> ITRF2014, you need an explicit concatenated operation chaining the 3 individual steps.



In fact, in PROJ the ETRS89 -> ETRF2000 -> ITRF2000 -> ITRF2014 route gives identical results to ETRS89 -> ETRF2000 -> ITRF2014, and this also has only one intermediate CRS:



projinfo -s epsg:7931 -t epsg:7912

Operation No. 1:

unknown id, Conversion from ETRF2000 (geog3D) to ETRF2000 (geocentric) + Inverse of ITRF2014 to ETRF2000 (1) + Conversion from ITRF2014 (geocentric) to ITRF2014 (geog3D), 0 m



projinfo -s epsg:8403 -t epsg:7912

Operation No. 1:

unknown id, Conversion from ETRF2014 (geog3D) to ETRF2014 (geocentric) + Inverse of ITRF2014 to ETRF2014 (2) + Conversion from ITRF2014 (geocentric) to ITRF2014 (geog3D), 0 m



If it is not the number of steps, what makes PROJ not choose ETRS89 -> ETRF2000 -> ITRF2014 but  ETRS89 -> ETRF2014 -> ITRF2014 instead? And what would need to be changed in the database to change that transformation route?



Jochem


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