[gdal-dev] Changes in SRS handling w.r.t TOWGS84

[Nyall Dawson]

On Wed, 18 Dec 2019 at 04:37, Even Rouault <even.rouault at spatialys.com> wrote:
>
> Hi,
>
> Following a number of exchanges on the PROJ mailing list, related to PROJ 6
> integration in QGIS, I've prepared a pull request changing a bit how we deal
> with the 'early-binding' TOWGS84 term in
> https://github.com/OSGeo/gdal/pull/2113
>
> The aim is to avoid the propagation of potentially suboptimal TOWGS84 terms by
> default (except when exporting to PROJ4 string as we don't have a more
> expressive way of encoding datum information), which can be the source of
> later problems (not using grids when available due to this towgs84 being
> strictly honoured).
>
> I've a backport of this for the 3.0 branch ready, to go in the 3.0.3 release.

Even -- I think this is totally the right move (from my (partial!)
understanding of the problem), as it means that downstream clients
like QGIS will be able to grab a lossless representation of the
original dataset's CRS via WKT.

I'd be happy to follow this logic in QGIS too, i.e. if coming from a
WKT definition then a bound CRS != its source CRS, but if coming from
a proj string then a bound crs == its source crs. That'd give much
desired consistency across the different tools.

Thanks for working through this!

Nyall



>
> Even
>
> --
> Spatialys - Geospatial professional services
> http://www.spatialys.com
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