Hi Klaus Thanks a lot, works pefect! collect_gemetries() and the other way around did the trick. Thanks also for the hint with the geometry generator. Bruno
> Date: Thu, 4 Apr 2024 12:01:21 +0000 > From: Klaus Affeldt <k...@ansperger.de> > To: "qgis-user@lists.osgeo.org" <qgis-user@lists.osgeo.org> > Subject: [Qgis-user] Calculate intersecting area of two layers in a > virtual field. Context of @geometry in overlay_intersects() > Message-ID: <5bcb1461d75f470bb86c03fc07b2c...@ansperger.de> > Content-Type: text/plain; charset="iso-8859-1" > > Hello Bruno, > > try it the other way around: > > coalesce( > area( > intersection( > @geometry, > collect_geometries( > overlay_intersects( > 'forest', > @geometry > ) > ) > ) > ), > 0 > ) > > In addition you can use the inner part in the geometry generator. > So you have a visual help to compare your results: > > intersection( > @geometry, > collect_geometries( > overlay_intersects( > 'forest', > @geometry > ) > ) > ) > > Mit freundlichen Gr??en > > Ihre PV ANSPERGER mbH > Klaus Affeldt > > Zentrale Kamp-Lintfort > S?dstra?e 25 > 47475 Kamp-Lintfort > Tel. +49 2842 9635-14 > https://www.ansperger.de > > A============================================================================================== > >> > >> Dear list > >> > >> Great, how powerful expressions are in QGIS! > >> I have two polygon layers, one with parcels and one with forests. In a > >> virtual field of the layer parcels I'm trying to calculate the area > >> covered with forest. I can sum the area of intersecting forests in a > >> virtual field with the follwing expression: > >> > >> coalesce( > >> array_sum( > >> overlay_intersects( > >> layer:= 'forest', > >> expression:= area(@geometry) > >> ) > >> ) > >> , 0) > >> > >> But @geometry doesen't return the intersecting area. It returns the whole > >> polygons, that partly intersect the parcel. So I could add an additional > >> intersection(): > >> > >> coalesce( > >> array_sum( > >> overlay_intersects( > >> layer:= 'forest', > >> expression:= area( > >> intersection( > >> @geometry, geometry(get_feature_by_id() > >> ) > >> ) > >> ) > >> ) > >> , 0) > >> > >> @geometry is calculated in the context of the layer forests. How could I > >> access the geometry of the parcel inside of overlay_intersects()? > >> get_feature_by_id() doesn't seem to help, since I don't see a way to get > >> the actual ID of the parcel. > >> It is not possible to return @geometry as expression in overlay_intersects > >> and do the intersection outside. > >> > >> Does any one have an idea, how I could get the intersected area? > >> Thank you. Bruno _______________________________________________ QGIS-User mailing list QGIS-User@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
