[PROJ] Serious confusion regarding towgs or not...!

[Nyall Dawson]

On Tue, 17 Dec 2019 at 23:39, Even Rouault <even.rouault at spatialys.com> wrote:
>
> > Ah ah, that you rely entirely on PROJ to do always the "right thing" makes
> > me equally nervous :-)
> > Perhaps QGIS when ingesting a WKT1 string with a TOWGS84[] or a PROJ.4
> > string with a +towgs84 should ask the user: "do you really want to use that
> > precise transformation to WGS84 (which will thus make it the pivot CRS for
> > datum transformations) or just use the underlying CRS and being proposed
> > with several possibilities when transforming to other datums ?" Of course
> > most users will have no clue at answering that question... Sometimes users
> > implictly relied on the more or less arbitrary +towgs84 values that were
> > picked up previously, and they will suffer from misalignment if using other
> > transformations. So perhaps there should be a different behaviour if
> > opening old QGIS projects than if creating new ones ? Just brainstorming
>
> Thining about all the above, regarding GDAL, I've issued the following pull
> request that will change its behaviour regarding importFromEPSG(), to no
> longer try to attach a transformation to WGS84:
>
> https://github.com/OSGeo/gdal/pull/2113

Thanks -- I'm confident this is a good move, and will adapt QGIS to
suit this logic too...

Nyall