Feature Request for OGRLayer: Add functions considering SetAttributeFilter() in GetExtent()

[tschmetzer]

This is to request and discuss an additional modified version of GetExtent() and GetFeatureCount().

I would suggest to call them GetFilteredExtent() and GetFilteredFeatureCount().

Especially the GetFilteredExtent() functionality would be very valuable to have. The handling of large GPKG layer files of several or dozens of GB would benefit from a tailored function.

Background: Currently the only way to get an extent or feature count on a subset is to set a subset via the OGRLayer::SetAttributeFilter()and then iterate over the whole subset doing a subsequent GetNextFeature(). These functions will of course only make sense if an existing spatial index of the layer's features can be used to highly speed up the extent calculation and feature count or any other optimization that can be found.

Issues like this could be speed up: https://github.com/qgis/QGIS/issues/46393

[jratike80]

From GeoPackage and SpatiaLite the extent is already available very fast from the rtree index.

select min(minx) from rtree_kunta_geom
where id in
(select id from kunta limit 100)

Example using ogrinfo ogrinfo -sql "select min(minx) from rtree_rakennus_geom where id in (select fid from rakennus limit 10000)" mtkmaasto.gpkg

Similarly count ogrinfo -sql "select count(*) from rakennus where sijaintitarkkuus=3000" mtkmaasto.gpkg

[rouault]

The GetFeatureCount() method already takes into account attribute and spatial filters in the GPKG driver. If an attribute filter is set, GetFeatureCount() efficiency will depend on the existence of an index on the filtered column(s). It is true that GetExtent() doesn't take into account attribute or spatial filters