Assuming that it does not happen in the main area of Ireland...I guess it is because it is outside of the area of usage of the datum transformation https://epsg.org/transformation_1641/TM65-to-WGS-84-2.html Probably (this is just a guess) gdalwarp is not taking it into consideration, making a ballpark transformation between TM65 and WGS84, while ogr2ogr doesn't.
On Wed, 8 Nov 2023 at 13:35, Sam Hall via gdal-dev <gdal-dev@lists.osgeo.org> wrote: > 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 > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/gdal-dev >
_______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/gdal-dev
