[GIS] Selecting features within certain buffer distance of selected feature using PyQGIS

lineproximitypyqgisselect-by-location

I have a shapefile of thousands of polylines. I have select one feature, I want to select all other features that is within say 100m of the selected feature.

How do I achieve it by pyqgis?

Best Answer

If you want to select all features that are within 100 m of the selected "buffer" feature you can use next code:

layer = iface.activeLayer()

feats = [ feat for feat in layer.getFeatures() ]

#selected feature fid = 0
geom_buffer = feats[0].geometry().buffer(100, -1)

#erasing selected feature in original list
del feats[0]

new_feats = [feat for feat in feats
             if feat.geometry().intersects(geom_buffer) ]

epsg = layer.crs().postgisSrid()

uri = "LineString?crs=epsg:" + str(epsg) + "&field=id:integer""&index=yes"

mem_layer = QgsVectorLayer(uri,
                           'line',
                           'memory')

prov = mem_layer.dataProvider()

for i, feat in enumerate(new_feats):
    feat.setAttributes([i])

prov.addFeatures(new_feats)

QgsMapLayerRegistry.instance().addMapLayer(mem_layer)

It produces a memory layer with features that match this condition.

I tried out above code with next line layer; where selected feature (id=0) was previously visualized as buffer by using its WKT format into QuickWKT plugin of QGIS.

After running the code, memory layer (red layer in next image) was obtained as expected:

Related Solutions

ArcObjects Selection – Selecting Features by Location in ArcObjects

This will take multiple steps:

Get a cursor from you selection set

    public static IFeatureCursor GetSelectedFeatures(IFeatureLayer featureLayer)
{
    if (featureLayer == null) return null;
    IFeatureSelection fSel = (IFeatureSelection)featureLayer;
    ISelectionSet selSet = (ISelectionSet)fSel.SelectionSet;
    ICursor cursor = null;
    selSet.Search(null, false, out cursor);
    IFeatureCursor fCursor = cursor as IFeatureCursor;
    return fCursor;
}

Union and buffer the items in the cursor

public static IPolygon UnionShapes(IFeatureCursor cursor, double bufferDist)
{
    if (cursor == null) return null;
    IFeature pFeat = cursor.NextFeature();
    if (pFeat != null)
    {
        if (pFeat.Shape is IPoint)
        {
            ITopologicalOperator ptopBuffer = (ITopologicalOperator)pFeat.Shape;
            IPolygon pTempPoly = (IPolygon)ptopBuffer.Buffer(bufferDist);
            ITopologicalOperator ptopUnion = (ITopologicalOperator)pTempPoly;
            pFeat = cursor.NextFeature();
            while (pFeat != null)
            {
                ptopBuffer = (ITopologicalOperator)pFeat.Shape;
                pTempPoly = (IPolygon)ptopBuffer.Buffer(bufferDist);
                ptopUnion = (ITopologicalOperator)ptopUnion.Union(pTempPoly);
                pFeat = cursor.NextFeature();
            }
            return (IPolygon)ptopUnion;
        }
        return null;
    }
    return null;
}

Select the spatial filter on the new shape

   public static ISpatialFilter CreateSpatialFilter(IFeatureClass fc, IGeometry shape)
{
    if (fc == null) return null;
    ISpatialFilter sf = new SpatialFilterClass();
    sf.GeometryField = fc.ShapeFieldName;
    sf.Geometry = shape;
    sf.SpatialRel = esriSpatialRelEnum.esriSpatialRelIntersects;
    return sf;
}

Search on the feature class with the filter.

    public static IFeatureCursor GetSelectedItemsByShape(IFeatureClass fc, ISpatialFilter filter)
{
    try
    {
        if (filter == null) return null;
        if (fc == null) return null;
        IFeatureCursor fcursor = fc.Search(filter, true);
        return fcursor;
    }
    catch
    {
        return null;
    }
}

Then if you want to select the new features:

    public static ISelectionSet CursorToSelectionSet(IFeatureLayer layer, IFeatureCursor cursor)
{

    IFeatureSelection fSel = (IFeatureSelection)layer;
    if (cursor != null)
    {
        IFeature feat = cursor.NextFeature();
        while (feat != null)
        {
            fSel.Add(feat);
            feat = cursor.NextFeature();
        }
    }
    return fSel.SelectionSet;
}

Good Luck

Deleting Selected Features Using PyQGIS – How to Guide

You can loop over the iterator and get the id() for every feature in it:

with edit(layer):
    # build a request to filter the features based on an attribute
    request = QgsFeatureRequest().setFilterExpression('"DN" != 3')

    # we don't need attributes or geometry, skip them to minimize overhead.
    # these lines are not strictly required but improve performance
    request.setSubsetOfAttributes([])
    request.setFlags(QgsFeatureRequest.NoGeometry)

    # loop over the features and delete
    for f in layer.getFeatures(request):
        layer.deleteFeature(f.id())

or with QGIS < 2.12

request = QgsFeatureRequest().setFilterExpression('"DN" != 3')
request.setSubsetOfAttributes([])
request.setFlags(QgsFeatureRequest.NoGeometry)

ids = [f.id() for f in layer.getFeatures(request)]

layer.startEditing()
for fid in ids:
    layer.deleteFeature(fid)
layer.commitChanges()

Best Answer

Related Solutions

ArcObjects Selection – Selecting Features by Location in ArcObjects

Deleting Selected Features Using PyQGIS – How to Guide

or with QGIS < 2.12

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