[QGIS-Developer] proj5 and epsg:3857 ?

[Even Rouault]

On vendredi 9 mars 2018 12:19:09 CET Richard Duivenvoorde wrote:
> Hi All,
> 
> I second that: not blaming anybody here. This happens in the real world.
> 
> My point was that I think as QGIS we can 'hide' this issue by not using
> 5.0.0 'yet' in the osgeo4w package.
> 
> I will happily use/test whatever is available in Debian sid  :-)
> 
> Also tried Kristian's fix.
> 
> For QGIS users: QGIS does not use the epsg file provided by your proj
> install, but a srs.db:
>  {QGISINSTALLDIR}/share/qgis/resources/srs.db
> 
> I edited (using DB browser) and removed the "+nadgrids=@null" clause
> from the epsg:3857 line.
> Checked by looking into the srs chooser of QGIS and seeing that it was
> indeed not visible anymore.
> 
> But it does not seem a 100% hack with me. While more near the 'real'
> place, it is still 150m off?
> 

I don't think the removal of "+nadgrids=@null" is a "universal" workaround. It only works 
when the other SRS has no +towgs84 or +nadgrids clause itself, which isn't the case of EPSG:
28992. Basically if you transform between EPSG:28992 and WebMercator without 
+nadgrids=@null, then no datum shift at all is done, so you have just the tranform between 
the Bessel ellipsoid and the sphere of radius 6378137. The proper fix is to get the patched 
version of proj

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