Make "Filter by geometry type" alg also available via Processing Toolbox

[pathmapper]

Description

Currently the very useful algorithm Filter by geometry type is not available via the Processing Toolbox but there are use cases for having it also there, e.g. splitting a WFS layer with mixed feature geometries into single layers.

Examples:

• WFS: https://xplanung.freiburg.de/xplansyn-wfs/services/xplansynwfs

• Feature type: xplan:BP_AnpflanzungBindungErhaltung
  

• Feature type: xplan:BP_Bereich
  

[pathmapper]

Test failure seems unrelated -> #48778 (comment)

[nyalldawson]

I must admit I'm a little confused by this 😄

QGIS doesn't really have support for mixed geometry type layers right now (ideally we would!), and all the sources which support mixed geometry types require you to manually select which geometry type you want for the layer when you load that source into a project.

How are you getting a mixed geometry type layer in the first place as a source for running the algorithm?

[pathmapper]

Oh, sorry that it's not clear from the PR description. The WFS used for the examples above is not under my control and has changed since then (currently no features for feature type: xplan:BP_AnpflanzungBindungErhaltung)

Short answer: from WFS sources

Long version:

There are WFS around which are serving feature types with mixed geometry types. If you load them with QGIS (via WFS connection), there's no dialogue which require you to manually select which geometry type you want for the layer. Instead one layer containing all available geometry types is added.

The type of the added layer is either one geometry type like point, linestring, polygon, ... (I guess this is determined by the geometry type of the first feature in the WFS response document) or QGIS sometimes adds a layer with the following "mixed geometry icon":

Here's a screencast demonstrating this (unfortunately this WFS is not publicly available, here the WFS response saved as file
wfs_response.zip ).

Please note that the type for the added layer is Point but it contains also lines and polygons. The lines and polygons are not rendered on the canvas but included in the attribute table and feature count.

If you execute the Filter by geometry type algorithm on it, you get this sorted out (last part of the screencast).

demonstration_mixed_wfs.mp4

Mixed geometry type layers from WFS source are currently a pain point in QGIS, here are two issues related to this:

• [WFS] Layer is added incorrectly as mixed geometry collection #49335
• [WFS] Wrong geometry type for layer / missing Mixed Geometry WFS Support  #49328

The Filter by geometry type algorithm relieves this pain point a bit.

all the sources which support mixed geometry types require you to manually select which geometry type you want for the layer when you load that source into a project

According to this, it sounds like the missing selection dialog for WFS sources with mixed geometry types is a bug.

If you drag a file with the WFS response of the screencast sample wfs_response.zip into QGIS, it shows the following dialog:

Having such a dialog for layers with mixed geometries from WFS sources would be great and there would be no need anymore to work around with the Filter by geometry type algorithm.

[pathmapper]

Found another publicly available WFS which is serving mixed geometry types for a feature type:

WFS endpoint: http://xplanung.lkee.de/xplansyn-wfs/services/xplansynwfs

Feature type: xplan:BP_AnpflanzungBindungErhaltung

[nyalldawson]

@pathmapper

Fair enough, that's a valid explanation!

[github-actions]

@pathmapper
This pull request has been tagged as requiring documentation.

A documentation ticket will be opened at https://github.com/qgis/QGIS-Documentation when this PR is merged.

Please update the description (not the comments) with helpful description and screenshot to help the work from documentors.
Also, any commit having [needs-doc] or [Needs Documentation] in will see its message pushed to the issue, so please be as verbose as you can.

Thank you!

[github-actions]

@pathmapper
A documentation ticket has been opened at qgis/QGIS-Documentation#7674
It is your responsibility to visit this ticket and add as much detail as possible for the documentation team to correctly document this change.
Thank you!