[QGIS-Developer] timzonefinder vs point in polygon

[C Hamilton]

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 <nyall.dawson at gmail.com>
> wrote:
> >>
> >> On Sat, 6 Feb 2021 at 07:54, Andrea Giudiceandrea <
> andreaerdna at libero.it> 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
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