[gdal-dev] Discrepancy when tiling on MAC and Linux

[Even Rouault]

On mercredi 13 novembre 2019 13:18:52 CET Grégory Bataille wrote:
> Hey Even,
> 
> So I can confirm that this is the issue
> On Mac
> OGRCT: Selecting transformation +proj=pipeline +step +proj=axisswap
> +order=2,1 +step +inv +proj=tmerc +lat_0=0 +lon_0=12 +k=1 +x_0=4500000
> +y_0=0 +ellps=bessel +step +proj=unitconvert +xy_in=rad +xy_out=deg +step
> +proj=axisswap +order=2,1 (Inverse of 3-degree Gauss-Kruger zone 4 + DHDN
> to WGS 84 (2) + Inverse of Transformation to WGS84)
> 
> On my linux docker
> OGRCT: Selecting transformation +proj=pipeline +step +proj=axisswap
> +order=2,1 +step +inv +proj=tmerc +lat_0=0 +lon_0=12 +k=1 +x_0=4500000
> +y_0=0 +ellps=bessel +step +proj=hgridshift +grids=BETA2007.gsb +step
> +proj=push +v_3 +step +proj=cart +ellps=WGS84 +step +inv +proj=helmert
> +x=598.1 +y=73.7 +z=418.2 +rx=0.202 +ry=0.045 +rz=-2.455 +s=6.7
> +convention=position_vector +step +inv +proj=cart +ellps=bessel +step
> +proj=pop +v_3 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step
> +proj=axisswap +order=2,1 (Inverse of 3-degree Gauss-Kruger zone 4 + DHDN
> to WGS 84 (4) + Inverse of Transformation to WGS84)
> 
> Now this is a problem to me and I don't quite know what to do with it.
> 
> So I have a fully specified dataset, that gives a TOWGS84, that my user has
> chosen (properly or not)
> Once the dataset is using this representation, I can't have auto projection
> because those will/might depend on the application using the dataset.
> Currently (most of) my backend processes are in Gdal3 / Proj6 and therefore
> (per my understanding), the TOWGS84 might be overriden
> However my front end processes only have some proj4 equivalence and will
> trust exactly the dataset.
> 
> I'm a bit at a loss to know what I should do.
> Should I do a gdalwarp step for gdal to "chose" the best projection and get
> a new dataset (with another TOWGS84) that I use internally for alignment,
> while giving the client the one he has asked for when he wants to get the
> raw dataset?
> 
> Do you have any ideas/recommandations? Is there a way to disable the PROJ6
> auto-selection feature?

This is not a PROJ6 issue, but a GDAL one related to the logic starting at
https://github.com/OSGeo/gdal/blob/master/gdal/ogr/ogrct.cpp#L843

You could try to add a test that if OGRSpatialReference::GetTOWGS84() returns 
OGRERR_NONE then the resolution to the WKT of the EPSG code is skipped

Even

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