[Qgis-psc] Grant progress report: Add vertical CRS handling to QGIS

[Régis Haubourg]

Wow Nyall. This is huge.
We will have to make some noise in the deodetic and topographic communities
that QGIS is now fully z aware.
Thanks for the very clear explanations and the cautious path you took to
avoid regressions.
Hats off
Régis

Le jeu. 1 août 2024, 05:26, Nyall Dawson via QGIS-PSC <
qgis-psc at lists.osgeo.org> a écrit :

> PSC,
>
> I'm writing to provide an update on the grant for QEP 267 -- Add vertical
> CRS handling to QGIS.
>
> This project has been underway since the grant application, with work
> being slowly "drip-fed" into QGIS over the last year's worth of releases.
> All work has been done in a step-by-step, atomic approach, to ensure that
> every little part of it is thoroughly reviewed and that no regressions have
> been introduced before moving to the next step. This approach was taken to
> reduce the risk of regressions in our critical transformation code. I've
> been carefully monitoring the issue tracker after each part is merged (and
> after each stable release during this time) to watch for any regression
> reports, and thankfully we've avoided them so far!
>
> Work which has been completed to date includes:
>
> - As of QGIS 3.34, QGIS can now create and handle vertical and compound
> CRSes. (Prior to this work QGIS was limited to creation and handling of
> horizontal CRS only, for various legacy reasons). There are a range of new
> PyQGIS API calls which make creation of vertical and compound CRS easy, and
> to make it possible to eg query the vertical component of an existing
> compound CRS.
> - In QGIS 3.36 the coordinate reference selection widgets were updated to
> offer choices of 2d only, compound, or vertical only CRSes. We use these in
> QGIS itself, but plugins can now also offer users choices of eg "pick a
> vertical CRS" where ONLY vertical CRSes are offered.
>  - In QGIS 3.34 coordinate transforms were reworked so that they function
> correctly with vertical transformation, if both the source and destination
> CRS have vertical components. (We delegate the actual transformation to
> PROJ, but QGIS itself no longer gets in the way and forces 2d only
> transformations!)
>   - In version 3.38 we introduced a new setting for QGIS projects, for
> their vertical reference system. Users can control this through project
> properties, and it's accessible via PyQGIS and via associated expression
> variables (eg @project_vertical_crs) for use in print layouts.
> - Similarly, in 3.38 we introduced the API support for map layers to have
> a vertical CRS. (This was not exposed to users in 3.38 though)
> - In QGIS 3.40 so far we have exposed the vertical CRS setting for vector
> layers to users (via the layer properties dialog), allowing users to
> specify the associated vertical CRS for these layers. The vertical CRS is
> respected in elevation profile plots, in Identify tool results, and in 3D
> Map views (assuming the 3D map is created with an associated vertical CRS).
> - There is an open pull-request for 3.40 to expose the vertical CRS for
> point cloud layers in a similar way, with the vertical CRS being respected
> in elevation profiles, identify tool results, and 3D map views
> - We have open pull requests for 3.40 to show layer vertical CRS
> information in the layer properties "information" pages, and add expression
> variables at the layer scope (eg @layer_vertical_crs).
>
> While the work conducted to date satisfies the original target
> deliverables of the grant*, we also accounted for follow ups to this work
> as user feedback and tickets are submitted. We'll continue to monitor the
> QGIS issue tracker and mailing lists for these reports, and (where
> appropriate) will address them in future releases.
>
> Kind regards,
> Nyall
>
> * We've gone a little further than the original deliverables here, and
> have implemented some of the functionality originally identified as "out of
> scope"! 😁
>
>
>
>
>
>
>
>   - QGIS map layers also have individual settings for the vertical
> reference system. This isn't YET exposed for user control. Before I expose
> this setting I want to ensure that the layer type correctly uses vertical
> transforms in the elevation profiles, in 3d views, and in the identify tool
> z values. This will definitely be done for vector layers in 3.40, (and
> hopefully the other layer types too)
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