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

[Zoltan Szecsei]

Hi,
Just by way of finality:

The CRS of the polygon SHP was not what it was purported to be.
I found that the .prj file was invalid when opening it in QGIS - maybe 
next time I will first look at the maps I am given, rather than just 
dive into python scripting.

All working as expected, now.

Thanks to those who gave ideas to try.

Kind regards,
Zoltan

On 2024/08/25 19:44, Zoltan Szecsei via QGIS-User wrote:
> 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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