Transforming from epsg:4326 to epsg:31468 produces a 2 meter offset according to QGIS

[arminus]

I have an input polygon in epsg:31468 which I need to transform to epsg:4326, the code I'm currently using is this:

project = pyproj.Transformer.from_proj(
    pyproj.Proj(init='epsg:31468')
    pyproj.Proj(init='epsg:4326'))
poly = transform(project.transform, poly)

Loading both polygons into QGIS, I get an offset of ~ 2 meters for every point, though.

I got a suggestion on reddit /r/gis, that I may also need a datum transformation by using a towgs parameter - but I don't know which value I need to pick.

And there was another comment wether pyproj actually allows datum transformations?

Any help is appreciated!

[snowman2]

pyproj does take into account datum transformations. The grids may help with accuracy: https://pyproj4.github.io/pyproj/stable/transformation_grids.html

I may also need a datum transformation by using a towgs parameter

This is no longer needed in PROJ 6+ from what I understand. I would recommend asking the PROJ mailing list for clarification on that: https://lists.osgeo.org/mailman/listinfo/proj/

Side note: This is the recommended pyproj 2+ method for creating transformer to use with shapely/pygeos transform:

project = pyproj.Transformer.from_crs("EPSG:31468", "EPSG:4326", always_xy=True)
poly = transform(project.transform, poly)

[snowman2]

https://gdalbarn.com/ : see section on "WGS84 Pivot"

[snowman2]

Forwarded: https://lists.osgeo.org/pipermail/proj/2021-April/010169.html