[PROJ] How to do Helmert transformation with +exact option in QGIS?

[Nyall Dawson]

On Wed, 10 Feb 2021 at 08:45, Kristian Evers <kreve at sdfe.dk> wrote:
>
>
>
> On 9 Feb 2021, at 23:40, Nyall Dawson <nyall.dawson at gmail.com> wrote:
>
> On Wed, 10 Feb 2021 at 04:56, Kristian Evers via PROJ
> <proj at lists.osgeo.org> wrote:
>
>
> Jochem,
>
> There is no +towgs84 equivalent of +exact. One of the many reasons to not use the old style syntax. Unfortunately that doesn’t solve your problem with QGIS. Unfortunately the QGIS custom CRS is still based on the PROJ.4 way of thinking (as far as I know, it’s been a while since I last tried it)
>
>
> Actually since 3.10 we've also supported direct WKT(2) definitions of
> custom CRS, and the GUI strongly pushes users towards defining custom
> projections using WKT over PROJ now :)
>
>
> Well that’s good news! Any chance I might be able to define my own PROJ transformation pipeline between a layer CRS and the project CRS then? That’d be handy from time to time and would probably also fix Jochems problem.

That's still an open feature request (
https://github.com/qgis/QGIS/issues/31106), although it's purely a GUI
limitation really.

Nyall


>
> /Kristian
>