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<p>Great thanks a lot !</p>
<p>I also think that something like GRIB2 would be nice for NetCDF. I will take note of this for future improvement to the NetCDF driver :)</p>
<p>LP </p>
<div class="moz-cite-prefix">On 2020-04-23 14:46, Even Rouault wrote:<br>
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Louis-Philippe,</p>
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> I did some more tests with the rotated_pole.nc in gdal GitHub repo</p>
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> (<a class="moz-txt-link-freetext" href="https://github.com/OSGeo/gdal/tree/master/autotest/gdrivers/data">https://github.com/OSGeo/gdal/tree/master/autotest/gdrivers/data</a>) just to</p>
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> make sure the issue was not with my data.</p>
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> </p>
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> With the new versions, the EXTENSION is missing from the WKT, which I guess</p>
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> makes the reprojection fail when I try to view it in Qgis ?</p>
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Kind of... I confirm the issue. A complex interaction between GDAL and PROJ due to the netCDF driver using a non-standard way of expressing a rotated pole CRS.</p>
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Well, there isn't really a standardized way, but what I did for GRIB2 recently was more in the right direction (hopefully!)</p>
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So to address the issue, I've done 2 things:</p>
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- a fix for GDAL (in time for 3.1.0): <a class="moz-txt-link-freetext" href="https://github.com/OSGeo/gdal/pull/2438">
https://github.com/OSGeo/gdal/pull/2438</a></p>
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- and one for PROJ: <a class="moz-txt-link-freetext" href="https://github.com/OSGeo/PROJ/pull/2185">
https://github.com/OSGeo/PROJ/pull/2185</a></p>
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The GDAL fix should probably be sufficient without the PROJ one, but I won't bet too much on that...</p>
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Ultimately the netCDF driver should be improved similarly to the GRIB one, that is creating a DERIVINGCONVERSION["Pole rotation (netCDF convention)"] instead of a hack.</p>
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So with both I now get with gdalinfo:</p>
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[...]</p>
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Coordinate System is:</p>
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GEOGCRS["unnamed",</p>
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BASEGEOGCRS["unknown",</p>
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DATUM["unknown",</p>
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ELLIPSOID["unknown",6367470,0,</p>
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LENGTHUNIT["metre",1,</p>
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ID["EPSG",9001]]]],</p>
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PRIMEM["Greenwich",0,</p>
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ANGLEUNIT["degree",0.0174532925199433],</p>
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ID["EPSG",8901]]],</p>
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DERIVINGCONVERSION["unknown",</p>
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METHOD["PROJ ob_tran o_proj=longlat"],</p>
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PARAMETER["lon_0",18,</p>
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ANGLEUNIT["degree",0.0174532925199433,</p>
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ID["EPSG",9122]]],</p>
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PARAMETER["o_lon_p",0,</p>
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ANGLEUNIT["degree",0.0174532925199433,</p>
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ID["EPSG",9122]]],</p>
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PARAMETER["o_lat_p",39.25,</p>
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ANGLEUNIT["degree",0.0174532925199433,</p>
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ID["EPSG",9122]]]],</p>
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CS[ellipsoidal,2],</p>
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AXIS["longitude",east,</p>
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ORDER[1],</p>
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ANGLEUNIT["degree",0.0174532925199433,</p>
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ID["EPSG",9122]]],</p>
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AXIS["latitude",north,</p>
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ORDER[2],</p>
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ANGLEUNIT["degree",0.0174532925199433,</p>
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ID["EPSG",9122]]]]</p>
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[...]</p>
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Upper Left ( -35.4700000, 23.6500003) ( 55d 6'46.50"W, 56d15'18.83"N)</p>
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Lower Left ( -35.4700000, -23.8699996) ( 16d 4'19.39"W, 18d42'19.70"N)</p>
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Upper Right ( 24.8100002, 23.6500003) ( 78d43'49.95"E, 63d51'22.90"N)</p>
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Lower Right ( 24.8100002, -23.8699996) ( 42d35'19.21"E, 22d45'11.78"N)</p>
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Center ( -5.3299999, -0.1099997) ( 9d37'52.99"E, 50d20'18.47"N)</p>
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The corner transformed in (non-rotated) geographic coordinates are now the same as GDAL 2.4, whereas before the fix, they were centered close to (0,0) as you mentionned.</p>
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Even</p>
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-- </p>
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Spatialys - Geospatial professional services</p>
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<a class="moz-txt-link-freetext" href="http://www.spatialys.com">http://www.spatialys.com</a></p>
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