Hi Calvin,
Thanks for sending me this from the Developers list. I am not a part of the Developer list, so I did not see the Join attribute by location tip from Andrea. Anyway, what do you mean with not getting fast result with single point lookups? When I select a single point from the 10000 point layer and run the same algorithm (check the selected features only option in the dialogue box), the result takes 0.05 seconds (12 seconds for all 10000). At least that is what is says in the log tab of the algorithm. And it sure looks quick. Jeroen Van: C Hamilton <[email protected]> Verzonden: dinsdag 9 februari 2021 16:25 Aan: Nyall Dawson <[email protected]> CC: Andrea Giudiceandrea <[email protected]>; qgis-developer <[email protected]>; Groene Bij <[email protected]> Onderwerp: Re: [QGIS-Developer] timzonefinder vs point in polygon Nyall, Using "Join attributes by location" on a large set of points is fast, but if you are doing single point lookups it bothers me that I am not getting that fast of results in comparison to timezonefinder. The 10,000 points is intended to test the speed of many single point lookups. If I were going to actually do 10,000 point lookups I would use the Join attributes by location, but here are my results of single point lookups using timezonefinder vs. your method. Note that the assumption is that they can be anywhere in the EPSG:4326 bounding box. I am not trying to constrain them to the QGIS canvas. timezonefinder: 44 seconds Your method: 144 seconds Here is my code for each: timezonefinder from timezonefinder import TimezoneFinder import time tf = TimezoneFinder() l = iface.activeLayer() features = l.getFeatures() start_time = time.time() for f in features: pt = f.geometry().asPoint() name = tf.certain_timezone_at(lng=pt.x(), lat=pt.y()) print('Time {}'.format(time.time() - start_time)) Your method: import time tzlayer = QgsVectorLayer("W:\\My Documents\\GitHub\\timezone_speed_lookup_test\\timezones.gpkg", "timezones", "ogr") l = iface.activeLayer() features = l.getFeatures() start_time = time.time() for f in features: pt = f.geometry().asPoint() rect = QgsRectangle( pt.x()-0.0000000001, pt.y()-0.000000001, pt.x(),pt.y()) request = QgsFeatureRequest().setFilterRect(rect) zones_intersecting_bounding_box = tzlayer.getFeatures(request) for tz_feature in zones_intersecting_bounding_box: if tz_feature.geometry().intersects(rect): name = tz_feature[1] break print('Time {}'.format(time.time() - start_time)) I'd suggest using similar logic to what join attributes by location does internally. In pseudocode: search_point = ... search_bbox = QgsRectangle( search_point.x() - some tolerance, search_point.y() - some_tolerance, ... ) request = QgsFeatureRequest().setFilterRect(search_bbox) zones_intersecting_bounding_box = tz_layer.getFeatures(request) for time_zone_feature in zones_intersecting_bounding_box: if time_zone_feature.intersects(search_point): # found a hit! break This will take advantage of whatever spatial index you have on the time zone layer (e.g. the internal shapefile/gpkg/... index) There's quite a number of extra optimisations which could be done here if the speed isn't sufficient for mouse movements, e.g. you could fetch all the zone features in the canvas extent and "prepare" their geometries for ultra fast point in polygon tests, and then invalidate this cache and rebuild on each canvas extent change. But I'd only do that kind of thing if needed... Nyall > > Calvin > > On Fri, Feb 5, 2021 at 6:30 PM Nyall Dawson <[email protected] > <mailto:[email protected]> > wrote: >> >> On Sat, 6 Feb 2021 at 07:54, Andrea Giudiceandrea <[email protected] >> <mailto:[email protected]> > wrote: >> > >> > C Hamilton wrote >> > > Using the algorithm Vector->Geoprocessing Tools->Intersection: 4 minutes, >> > > 4 >> > > seconds >> > >> > Hi Calvin, >> > maybe it could be better to use the "Join attributes by location" >> > algorithm. >> > It only takes few seconds to preform the join. >> >> Confirmed - for me it only takes ~2 seconds, and that's on an >> non-optimised debug build! There may be a few % more performance boost >> on the proper QGIS release builds. >> >> "Join attributes by location" has a bunch of extra logic to optimise >> the method that the join is performed, which really pays off in this >> particular situation (matching points to polygons, where number of >> points >> number of polygons). >> >> Nyall >> >> >> >> > >> > Regards. >> > >> > Andrea >> > >> > >> > >> > -- >> > Sent from: http://osgeo-org.1560.x6.nabble.com/QGIS-Developer-f4099106.html >> > _______________________________________________ >> > QGIS-Developer mailing list >> > [email protected] <mailto:[email protected]> >> > List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer >> > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer >> _______________________________________________ >> QGIS-Developer mailing list >> [email protected] <mailto:[email protected]> >> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer >> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
_______________________________________________ Qgis-user mailing list [email protected] List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
