[PROJ] "Trustworthiness" of vertical transformations

[Nyall Dawson]

On Tue, 26 Nov 2019 at 20:52, Kristian Evers <kreve at sdfe.dk> wrote:

> You can get the transformation accuracy using the API function
> proj_coordoperation_get_accuracy(). I think it would be cool if
> information about transformation accuracy where readily available in
> software like QGIS (nudge, nudge :-))

That's where I'm coming from now... I'm just wondering if and how we
should expose vertical transformation functionality. Do you have any
ideas on what functionality you would expect an end-user application
to expose for vertical transformations?

Nyall

>
> /Kristian
>
> -----Original Message-----
> From: PROJ <proj-bounces at lists.osgeo.org> On Behalf Of Nyall Dawson
> Sent: 26. november 2019 01:27
> To: PROJ <proj at lists.osgeo.org>
> Subject: [PROJ] "Trustworthiness" of vertical transformations
>
> Hi list,
>
> I've seen a lot of activity on the PROJ repo lately relating to
> vertical datum transformations. Coming from zero knowledge about the
> world of vertical transformations... if I setup a simple
> transformation between two proj CRS objects created using auth/id
> codes, and transform a 3d point using proj_trans_generic... how
> "trustworthy" is the resultant z value?
>
> I've seen some examples (e.g in
> https://github.com/OSGeo/PROJ/issues/1743) which use a
> "EPSG:26911+5703" type construct, which leads me to believe that the
> world of vertical transformations is not so straightforward! Any tips
> to give a newbie entering this world to avoid the inevitable pitfalls
> which await?
>
> Cheers,
> Nyall
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