Raster labeling

[nyalldawson]

Allows raster pixels to be labeled with the value taken from a raster band.

Labels are registered with the labeling engine, so participate in label conflict resolution and overlap avoidance

Options include

• Selection of band to take values from
• Using QgsNumericFormat to customise the number format for the labels
• Uses text renderer, so supports buffers, shadows, etc
• Label priority
• Scale dependant visibility
• Optional pixel size dependent visibilty, ie show only when pixels are > 4mm in size
• Z index control, overlap avoidance mode
• Option for showing values resampled over neighbouring pixels

Fixes #14408

Funded by Canton de Neuchâtel

Peek.2024-12-05.15-41.mp4

[qgis-bot]

@nyalldawson

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[qgis-bot]

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

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[github-actions]

🪟 Windows builds

Download Windows builds of this PR for testing.
Debug symbols for this build are available here.
(Built from commit 236dbd6)

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
(Built from commit 236dbd6)

[saberraz]

Very nice feature. A couple of silly questions maybe:

• Does this work with expression engine. Lets say I have a temporal raster where times are stored as a band. Can I then show the raster pixel based on the band and then see the label changes as I move the temporal controller?!
• Will there be an option to merge the same labels for neighboring cells?

[nyalldawson]

@saberraz

Does this work with expression engine. Lets say I have a temporal raster where times are stored as a band. Can I then show the raster pixel based on the band and then see the label changes as I move the temporal controller?!

No -- right now the band selection is fixed, and you get the pixel values only. (There's kind-of expression support via the "custom expression" option in the number format panel, but that's limited).

I think it'd be nice for a follow up to add an expression based labels mode, so eg you can get all band values as a list and choose how to display these (but that's not in my current scope).

Will there be an option to merge the same labels for neighboring cells?

It's not planned, but I do have a follow up coming which will allow the labels to show downsampled values (eg labeling only every second pixel)

[saberraz]

Great work and thanks for the explanation.

[github-actions]

Tests failed for Qt 6

One or more tests failed using the build from commit 6d556ba

resampling

resampling

Test failed at test_render_resampled at tests/src/python/test_qgsrasterlabeling.py:324

Rendered image did not match tests/testdata/control_images/raster_labeling/expected_resampling/expected_resampling.png (found 9080 pixels different)

The full test report (included comparison of rendered vs expected images) can be found here.

Further documentation on the QGIS test infrastructure can be found in the Developer's Guide.

[nyalldawson]

I would LOVE a review before I leave on Christmas holidays on Friday please! (Otherwise this will likely miss 3.42 deadline, I'm away from my computer for a month)

Ping @nirvn @m-kuhn @3nids @alexbruy @troopa81

[nirvn]

@nyalldawson , I'll do it.

[nirvn]

A couple of comments.

We'll need the labeling panel to also be featured in the raster properties dialog before we ship the functionality.

But beyond that, big thanks! It's something I was looking for multiple times.

[nyalldawson]

@nirvn

We'll need the labeling panel to also be featured in the raster properties dialog before we ship the functionality.

Ok, done!

[qgis-bot]

@nyalldawson
A documentation ticket has been opened at qgis/QGIS-Documentation#9490
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!

[m-kuhn]

Thanks for this, I can think of a couple of times that would have been useful!

@nyalldawson