First timer - finding errors using python transforming from EPSG 9367 to 27700

[tomhaw]

Hi
I am using pyproj for the first time today and in converting between these two crs I appear to get an error of approximately 87m using using this code (I have made the crs references static for the moment):

from pyproj import Transformer

def convert_point_between_crs(point: list, from_crs:int , to_crs: int) -> list:
transformer = Transformer.from_crs("EPSG:9367", "EPSG:27700")
return list(transformer.transform(point[0], point[1], point[2]))

And this point
[187836.59959467375, 398967.2245705411, 0.0]

I'm not sure what I could be doing wrong. I believe the answer should be approx 368067.111, 391920.801 but the above code calculates it as 367981.264,391936.664

Any advice? Thanks

[djhoese]

There could always be something misconfigured through the transformation process or in the PROJ (the C library) database of EPSG definitions. Could you explain how/why you got the values you expect?

[tomhaw]

To get the coordinate I was expecting I used a cad package and it's in-built coordinate system and reprojection.

[djhoese]

Oh and what version of pyproj and the PROJ C library are you using?

[djhoese]

I get this with the command line cs2cs from PROJ:

$ echo "187836.59959467375 398967.2245705411" | cs2cs EPSG:9367 EPSG:27700
367980.61	391936.41 0.00

$ conda list proj
# packages in environment at /home/davidh/miniforge3/envs/satpy_py312:
#
# Name                     Version          Build            Channel
proj                       9.6.2            h18fbb6c_2       conda-forge
pyproj                     3.7.2            py312h1c88c49_1  conda-forge

[tomhaw]

pyproj version: 3.7.1
PROJ version: 9.5.1

[jjimenezshaw]

Do you have the file TN15-ETRS89-to-TPEN11-IRF.gsb next to proj.db (use PROJ_DATA to specify the paths)?

projinfo tells you this:

projinfo -s EPSG:9367 -t EPSG:27700 -o proj 
Candidate operations found: 2
-------------------------------------
Operation No. 1:

unknown id, Inverse of TPEN11-TM + Inverse of ETRS89 to TPEN11-IRF (1) + Inverse of OSGB36 to ETRS89 (2) + British National Grid, 0.03 m, United Kingdom (UK) - on or related to the Trans-Pennine rail route from Liverpool via Manchester to Bradford and Leeds., at least one grid missing

PROJ string:
+proj=pipeline
  +step +inv +proj=tmerc +lat_0=53.5 +lon_0=-2.25 +k=1 +x_0=203252.175
        +y_0=407512.765 +ellps=GRS80
  +step +inv +proj=hgridshift +grids=TN15-ETRS89-to-TPEN11-IRF.gsb
  +step +inv +proj=hgridshift +grids=uk_os_OSTN15_NTv2_OSGBtoETRS.tif
  +step +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000
        +ellps=airy

Grid TN15-ETRS89-to-TPEN11-IRF.gsb needed but not found on the system.
Grid uk_os_OSTN15_NTv2_OSGBtoETRS.tif needed but not found on the system. Can be obtained at https://cdn.proj.org/uk_os_OSTN15_NTv2_OSGBtoETRS.tif

-------------------------------------
Operation No. 2:

unknown id, Inverse of TPEN11-TM + Ballpark geographic offset from TPEN11-IRF to OSGB36 + British National Grid, unknown accuracy, World, has ballpark transformation

PROJ string:
+proj=pipeline
  +step +inv +proj=tmerc +lat_0=53.5 +lon_0=-2.25 +k=1 +x_0=203252.175
        +y_0=407512.765 +ellps=GRS80
  +step +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000
        +ellps=airy