[gdal-dev] Transforming from EPSG:29902 to EPSG:4326 at the limit of the area of use.

[Sam Hall]

I have some data that covers the whole of the Republic of Ireland, including the Blasket Islands off the West Coast, situated around 24439, 95540 in EPSG:29902. These islands straddle the western boundary of the area of use of the coordinate system -10.56° W.

When transforming a raster dataset from EPSG:29902 to EPSG:4326 using gdalwarp at gdal >= 3.5.2, there seems to be a roughly 50 m shift in the data at the area of use boundary, while if I use ogr2ogr on a vector copy of this data, I don't see this shift.

I have a reproducible example of this at https://gitlab.com/Sam.Hall1/29902_gdalwarp_vs_ogr2ogr.git. In this example I created a rectangular polygon with interpolated points and saved it to a shapefile, then used gdal_rasterize to create a GeoTiff. gdalwarp gives the desired result using a gdal 3.5.1 docker image. The full commands are in the docker-compose.yml in the repository but the parameter's I'm using are:

gdalwarp -t_srs EPSG:4326 -tr 0.000045 0.000045 -tap -overwrite input.tif output.tif
ogr2ogr -t_srs EPSG:4326 output.shp input.shp
 
I've also seen similar results when transforming from EPSG:27700 to EPSG:4326 in Jersey and Guernsey in the English Channel but I'd have to use a much earlier version of gdal to reproduce the desired result.

Is there a gridshift file or any additional parameters that I could use to get the output to look more continuous across the area of use line? 

Sam