Inconsistent transformations of coords between OSX and ubuntu

[gmmorris]

I'm not sure if this is a PROJ issue, or a georust issue, so cross-posting.

Example of problem

The code is identical in both cases, it's the result of the calculation that changes between OSX and ubuntu.
I'm using the convert API ion the Rust library - not sure what it maps to in the C library, sorry.

https://github.com/georust/proj/blob/aafff341ce6fccf887e0f9011dfbd55c069af761/src/proj.rs#L803

Problem description

I'm transforming geometries received in EPSG::27700 to OGC:1.3:CRS84.

I'm encountering some inconsistencies between my local environment (OSX) and my CI (ubuntu-latest on Github Actions).

Given this geometry:

{ "type": "Point", "coordinates": [492941.3929127551,144592.2391630347] }

Locally on OSX and transform these coords are transformed into:

{ "type": "Point", "coordinates": [-0.6713249654966993, 51.19300053717864] }

But then on CI they are transformed into:

{ "type": "Point", "coordinates": [-0.6713438264761399, 51.193003894930584] }

Any thoughts on why this inconsistency might be happening and how I can avoid it?

I'm happy to compromise on resolution (cm would be ideal, but meter could work if that helps), but mostly I want to understand if this is a rounding or configuration issue.

Cheers

[rouault]

The results depend if you have the uk_os_OSTN15_NTv2_OSGBtoETRS.tif available. The results on OSX are with the grids, the results on your CI are without it (less accurate)

cf

$ echo 492941.3929127551 144592.2391630347 | PROJ_DEBUG=2 PROJ_NETWORK=ON bin/cs2cs -d 10 EPSG:27700 EPSG:4326
pj_open_lib(proj.ini): call fopen(/home/even/proj/install-proj-master/share/proj/proj.ini) - succeeded
pj_open_lib(proj.db): call fopen(/home/even/proj/install-proj-master/share/proj/proj.db) - succeeded
pj_open_lib(uk_os_OSTN15_NTv2_OSGBtoETRS.tif): call fopen(uk_os_OSTN15_NTv2_OSGBtoETRS.tif) - failed
pj_open_lib(OSTN15_NTv2_OSGBtoETRS.gsb): call fopen(OSTN15_NTv2_OSGBtoETRS.gsb) - failed
pj_open_lib(uk_os_OSTN15_NTv2_OSGBtoETRS.tif): call fopen(uk_os_OSTN15_NTv2_OSGBtoETRS.tif) - failed
pj_open_lib(OSTN15_NTv2_OSGBtoETRS.gsb): call fopen(OSTN15_NTv2_OSGBtoETRS.gsb) - failed
Using https://cdn.proj.org/uk_os_OSTN15_NTv2_OSGBtoETRS.tif
Using coordinate operation Inverse of British National Grid + OSGB36 to WGS 84 (9)
pj_open_lib(uk_os_OSTN15_NTv2_OSGBtoETRS.tif): call fopen(uk_os_OSTN15_NTv2_OSGBtoETRS.tif) - failed
pj_open_lib(OSTN15_NTv2_OSGBtoETRS.gsb): call fopen(OSTN15_NTv2_OSGBtoETRS.gsb) - failed
Using https://cdn.proj.org/uk_os_OSTN15_NTv2_OSGBtoETRS.tif
51.1930005372	-0.6713249655 0.0000000000

vs

$ echo 492941.3929127551 144592.2391630347 | PROJ_DEBUG=2 bin/cs2cs -d 10 EPSG:27700 EPSG:4326
pj_open_lib(proj.ini): call fopen(/home/even/proj/install-proj-master/share/proj/proj.ini) - succeeded
pj_open_lib(proj.db): call fopen(/home/even/proj/install-proj-master/share/proj/proj.db) - succeeded
pj_open_lib(uk_os_OSTN15_NTv2_OSGBtoETRS.tif): call fopen(uk_os_OSTN15_NTv2_OSGBtoETRS.tif) - failed
pj_open_lib(OSTN15_NTv2_OSGBtoETRS.gsb): call fopen(OSTN15_NTv2_OSGBtoETRS.gsb) - failed
pj_open_lib(uk_os_OSTN15_NTv2_OSGBtoETRS.tif): call fopen(uk_os_OSTN15_NTv2_OSGBtoETRS.tif) - failed
pj_open_lib(OSTN15_NTv2_OSGBtoETRS.gsb): call fopen(OSTN15_NTv2_OSGBtoETRS.gsb) - failed
Using coordinate operation Inverse of British National Grid + OSGB36 to WGS 84 (9)
Attempt to use coordinate operation Inverse of British National Grid + OSGB36 to WGS 84 (9) failed. Grid uk_os_OSTN15_NTv2_OSGBtoETRS.tif is not available. Consult https://proj.org/resource_files.html for guidance. This might become an error in a future PROJ major release. Set the ONLY_BEST option to YES or NO. This warning will no longer be emitted (for the current transformation instance).
No inverse operation
Did not result in valid result. Attempting a retry with another operation.
Using coordinate operation Inverse of British National Grid + OSGB36 to WGS 84 (6)
51.1930038949	-0.6713438265 0.0000000000

Cf https://proj.org/en/9.2/resource_files.html and https://proj.org/en/9.2/usage/network.html

[gmmorris]

amazing, thanks for the quick response!