[Qgis-psc] Report on the grant for QEP 291

[Julien Cabieces]

Great work! thanks Mathieu

> Greetings PSC,
>
> I’m happy to report that the work for the above-mentioned QEP has been completed during the months of August and September 2024. The
> work includes:
>
> - A new “smart” network cache mode - enabled by default – which adopts modern browsers’ strategies to determine the on-disk network cache
> size based on users’ available space. Starting with QGIS, for the fast majority of users, this will increase the network cache size from 0.25gb to
> 1gb, which in turn will allow for greater space to cache XYZ raster tiles, including those served by openstreetmap.org. While a backport was
> made available, it was deemed – wisely :) - too risky to merge.
>
> - The following processing algorithms were modified to insure QGIS users do not accidentally breach the OSMF tile usage policy with regards to
> bulk downloads: the generate XYZ tiles (MBTiles) algorithm, the generate XYZ tiles (Directory) algorithm, and the convert map to raster
> algorithm. In all three algorithms, a check is now in place to insure that no more than 5,000 tiles will be fetched from openstreetmap.org. If the
> amount of tiles goes behind this threshold, users will be informed through a warning message in their processing algorithm dialog that the
> layer serving openstreetmap.org tiles has been removed from the set of layers being rendered. Below 5,000 tiles, we assume users are not
> aimed at bulk downloading tiles but rather preparing a map of reasonable extent for viewing. These changes have been backported to the
> current 3.34 LTR.
>
> - Additionally, further safeguards were put in place while researching other means through which bulk downloads could be achieved. The same
> 5,000 tiles threshold when saving a XYZ raster layer through the browser panel as well as through the layers panel when those tiles are served
> through openstreetmap.org. As with the processing algorithms, when users surpasses the threshold, a message box will appear to inform them
> of the OSMF tile usage policy. These changes are available in 3.40 and have also been backported to the current 3.34 LTR.
>
> - Finally, I took the opportunity to apply an improvement to the default OpenStreetMap XYZ layer available through the browser panel. On fresh
> QGIS installations, this layer now now has its tile resolution set to 96DPI instead of unknown. The change results in a significant reduction in
> tiles being fetched when exporting a print layout in high DPI (e.g. 300). The benefits in terms of tile fetching reduction also impacts atlas and
> report layout exports. The change arguably improves layout exports by avoiding tiny, unreadable labels. Users can always manually change this
> tile resolution setting if desired. This change is available in 3.40 and has also been backported to the current 3.34 LTR.
>
> With those improvements in place, QGIS 3.40 has the safeguards in place to insure that bulk downloads - accidental or intentional - are
> prohibited. Furthermore, the network caching improvement and the adjusted configuration of the default OpenStreetMap XYZ layer shipped
> with QGIS are undoubtedly going to reduce any stress caused by normal usage’s fetching of tiles.
>
> Regards,
>
> Mathieu Pellerin
> OPENGIS.ch
>
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-- 

Julien Cabieces
Senior Developer at Oslandia
julien.cabieces at oslandia.com