[Qgis-user] Python code to select polygon at location

[Zoltan Szecsei]

So as updated plan-of-attack as below.....

>     lyr_poly = QgsVectorLayer(poly_shp, '', 'Ogr') lyr_poly_si =
>     QgsSpatialIndex(lyr_poly.getFeatures(),
>     flags=QgsSpatialIndex.FlagStoreFeatureGeometries) # EPSG:4326 point = QgsPointXY(lon, lat)
>     point_rect = QgsGeometry.fromPointXY(point).buffer(0.001,5).boundingBox()
>     # feature_ids = lyr_poly_si.intersects(point_rect)# intersects wants rectangle requests = QgsFeatureRequest().setFilterFids(feature_ids)
>     # feature_idx = lyr_poly_si.nearestNeighbor(point,10,maxDistance=0.001)
>     requestx = QgsFeatureRequest().setFilterFids(feature_idx)

For the above code the lists feature_ids and feature_idx are always empty.
The Longitude and Latitude coords are correct, also for the box created 
from the Point.

I'd be grateful for any insight on why nothing is found.

Thanks in advance,
Zoltan


On 2024/08/25 16:19, Zoltan Szecsei via QGIS-User wrote:
> Hi,
> I'm doing my "once a year need to do something in python with QGIS" :-/
> Using QGIS 3.38 and PyCharm.
>
> I have a SHP file with 28000 polygons.
> *A SPREADSHEET file with 22000 Points (for which I am making a SHP 
> file and wanting attribute vaues from underlying polygons)*
> Both in EPSG:4326
>
> Without using QGIS processing, what is the quickest way to, for each 
> point 1 by 1, find the underlying polygon and read the attribute field 
> values of that polygon?
> The code snippet below is far too inefficient - but I cannot find code 
> that selects at XY and benefits from any spatial index on the polygons.
>
>     	lyr_poly = QgsVectorLayer(polygon_shp, '', 'Ogr')       point =
>     QgsPointXY(lon, lat)       request =
>     QgsFeatureRequest().setFilterRect(lyr_poly.extent())       for
>     feature in lyr_poly.getFeatures(request):           geom =
>     feature.geometry()           if
>     geom.contains(QgsGeometry.fromPointXY(point)):           
>     lyr_poly.select(feature.id())               print(f"Feature with
>     ID {feature.id()} is selected.")               break
>
> Thanks in advance,
> Zoltan
>
>
>
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-- 

=============================================
Zoltan Szecsei GPrGISc 0031
Director, Geograph (Pty) Ltd.
GIS and Photogrammetric Services

Cape Town, South Africa.

Mobile: +27-83-6004028 (Signal, not WhatsApp)
         +974-5058-8729
         +36-20-4808362

www.geograph.co.za
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