Rework Select by Location algorithm

Changes:

- handle different CRS transparently

- don't build a spatial index on the selection layer. Instead
only use feature requests to fetch features which are within
the desired bounds, and rely on the presence of an appropriate
spatial index at the provider's backend. Otherwise, we force
every user of this algorithm to have a full iteration of the
source table, regardless of how large the table is. That means
that trying to select a set of addresses which fall within
a specific locality from a table which contains the addresses
for a whole state will FORCE every address in the state to
be initially read before any calculation begins. With this
change only those features within the bounding box of the
selected localities will ever be fetched from the provider,
resulting in huge speed improvements for the algorithm.

- use prepared geometries for the spatial relation tests.
This dramatically speeds up the algorithm in the case
where the intersection layer features cover multiple
features from the 'selection' layer.

- Add a 'select within current selection' mode

- Optimise feature requests for efficiency (especially
with respect to the 'disjoint' selection mode)

Author: nyalldawson

python/plugins/processing/algs/qgis/QGISAlgorithmProvider.py

@@ -134,6 +134,7 @@
 from .SaveSelectedFeatures import SaveSelectedFeatures
 from .SelectByAttribute import SelectByAttribute
 from .SelectByExpression import SelectByExpression
+from .SelectByLocation import SelectByLocation
 from .ServiceAreaFromLayer import ServiceAreaFromLayer
 from .ServiceAreaFromPoint import ServiceAreaFromPoint
 from .SetMValue import SetMValue
@@ -167,7 +168,6 @@
 from .ZonalStatistics import ZonalStatistics
 
 # from .ExtractByLocation import ExtractByLocation
-# from .SelectByLocation import SelectByLocation
 # from .SpatialJoin import SpatialJoin
 
 pluginPath = os.path.normpath(os.path.join(
@@ -183,7 +183,6 @@ def __init__(self):
 
     def getAlgs(self):
         # algs = [
-        #         SelectByLocation(),
         #         ExtractByLocation(),
         #         SpatialJoin(),
         #         ]
@@ -281,6 +280,7 @@ def getAlgs(self):
                 SaveSelectedFeatures(),
                 SelectByAttribute(),
                 SelectByExpression(),
+                SelectByLocation(),
                 ServiceAreaFromLayer(),
                 ServiceAreaFromPoint(),
                 SetMValue(),

python/plugins/processing/algs/qgis/SelectByLocation.py

@@ -29,13 +29,19 @@
 
 from qgis.PyQt.QtGui import QIcon
 
-from qgis.core import QgsGeometry, QgsFeatureRequest, QgsProcessingUtils
+from qgis.core import (QgsGeometry,
+                       QgsFeatureRequest,
+                       QgsProcessingUtils,
+                       QgsProcessing,
+                       QgsProcessingParameterVectorLayer,
+                       QgsProcessingParameterFeatureSource,
+                       QgsProcessingParameterEnum,
+                       QgsProcessingParameterNumber,
+                       QgsProcessingOutputVectorLayer,
+                       QgsVectorLayer)
+
 
 from processing.algs.qgis.QgisAlgorithm import QgisAlgorithm
-from processing.core.parameters import ParameterSelection
-from processing.core.parameters import ParameterVector
-from processing.core.parameters import ParameterNumber
-from processing.core.outputs import OutputVector
 from processing.tools import vector
 
 pluginPath = os.path.split(os.path.split(os.path.dirname(__file__))[0])[0]
@@ -63,32 +69,43 @@ def initAlgorithm(self, config=None):
         self.predicates = (
             ('intersects', self.tr('intersects')),
             ('contains', self.tr('contains')),
-            ('disjoint', self.tr('disjoint')),
-            ('equals', self.tr('equals')),
+            ('disjoint', self.tr('is disjoint')),
+            ('isEqual', self.tr('equals')),
             ('touches', self.tr('touches')),
             ('overlaps', self.tr('overlaps')),
             ('within', self.tr('within')),
             ('crosses', self.tr('crosses')))
 
+        self.reversed_predicates = {'intersects': 'intersects',
+                                    'contains': 'within',
+                                    'disjoint': 'disjoint',
+                                    'isEqual': 'isEqual',
+                                    'touches': 'touches',
+                                    'overlaps': 'overlaps',
+                                    'within': 'contains',
+                                    'crosses': 'crosses'}
+
         self.methods = [self.tr('creating new selection'),
                         self.tr('adding to current selection'),
+                        self.tr('select within current selection'),
                         self.tr('removing from current selection')]
 
-        self.addParameter(ParameterVector(self.INPUT,
-                                          self.tr('Layer to select from')))
-        self.addParameter(ParameterVector(self.INTERSECT,
-                                          self.tr('Additional layer (intersection layer)')))
-        self.addParameter(ParameterSelection(self.PREDICATE,
-                                             self.tr('Geometric predicate'),
-                                             self.predicates,
-                                             multiple=True))
-        self.addParameter(ParameterNumber(self.PRECISION,
-                                          self.tr('Precision'),
-                                          0.0, None, 0.0))
-        self.addParameter(ParameterSelection(self.METHOD,
-                                             self.tr('Modify current selection by'),
-                                             self.methods, 0))
-        self.addOutput(OutputVector(self.OUTPUT, self.tr('Selected (location)'), True))
+        self.addParameter(QgsProcessingParameterVectorLayer(self.INPUT,
+                                                            self.tr('Select features from'), types=[QgsProcessing.TypeVectorAnyGeometry]))
+        self.addParameter(QgsProcessingParameterEnum(self.PREDICATE,
+                                                     self.tr('Where the features are (geometric predicate)'),
+                                                     options=[p[1] for p in self.predicates],
+                                                     allowMultiple=True, defaultValue=[0]))
+        self.addParameter(QgsProcessingParameterFeatureSource(self.INTERSECT,
+                                                              self.tr('By comparing to the features from'), types=[QgsProcessing.TypeVectorAnyGeometry]))
+        self.addParameter(QgsProcessingParameterNumber(self.PRECISION,
+                                                       self.tr('Precision'), type=QgsProcessingParameterNumber.Double,
+                                                       minValue=0.0, defaultValue=0.0))
+        self.addParameter(QgsProcessingParameterEnum(self.METHOD,
+                                                     self.tr('Modify current selection by'),
+                                                     options=self.methods, defaultValue=0))
+
+        self.addOutput(QgsProcessingOutputVectorLayer(self.OUTPUT, self.tr('Selected (by location)')))
 
     def name(self):
         return 'selectbylocation'
@@ -97,60 +114,61 @@ def displayName(self):
         return self.tr('Select by location')
 
     def processAlgorithm(self, parameters, context, feedback):
-        filename = self.getParameterValue(self.INPUT)
-        inputLayer = QgsProcessingUtils.mapLayerFromString(filename, context)
-        method = self.getParameterValue(self.METHOD)
-        filename2 = self.getParameterValue(self.INTERSECT)
-        selectLayer = QgsProcessingUtils.mapLayerFromString(filename2, context)
-        predicates = self.getParameterValue(self.PREDICATE)
-        precision = self.getParameterValue(self.PRECISION)
-
-        oldSelection = set(inputLayer.selectedFeatureIds())
-        inputLayer.removeSelection()
-        index = QgsProcessingUtils.createSpatialIndex(inputLayer, context)
+        select_layer = self.parameterAsVectorLayer(parameters, self.INPUT, context)
+        method = QgsVectorLayer.SelectBehavior(self.parameterAsEnum(parameters, self.METHOD, context))
+        intersect_source = self.parameterAsSource(parameters, self.INTERSECT, context)
+        # build a list of 'reversed' predicates, because in this function
+        # we actually test the reverse of what the user wants (allowing us
+        # to prepare geometries and optimise the algorithm)
+        predicates = [self.reversed_predicates[self.predicates[i][0]] for i in self.parameterAsEnums(parameters, self.PREDICATE, context)]
+        precision = self.parameterAsDouble(parameters, self.PRECISION, context)
 
         if 'disjoint' in predicates:
-            disjoinSet = []
-            for feat in QgsProcessingUtils.getFeatures(inputLayer, context):
-                disjoinSet.append(feat.id())
-
-        geom = QgsGeometry()
-        selectedSet = []
-        features = QgsProcessingUtils.getFeatures(selectLayer, context)
-        total = 100.0 / selectLayer.featureCount() if selectLayer.featureCount() else 0
+            disjoint_set = select_layer.allFeatureIds()
+        else:
+            disjoint_set = None
+
+        selected_set = set()
+        request = QgsFeatureRequest().setSubsetOfAttributes([]).setDestinationCrs(select_layer.crs())
+        features = intersect_source.getFeatures(request)
+        total = 100.0 / intersect_source.featureCount() if intersect_source.featureCount() else 0
         for current, f in enumerate(features):
-            geom = vector.snapToPrecision(f.geometry(), precision)
-            bbox = geom.boundingBox()
+            if feedback.isCanceled():
+                break
+
+            if not f.hasGeometry():
+                continue
+
+            engine = QgsGeometry.createGeometryEngine(f.geometry().geometry())
+            engine.prepareGeometry()
+            bbox = f.geometry().boundingBox()
             bbox.grow(0.51 * precision)
-            intersects = index.intersects(bbox)
 
-            request = QgsFeatureRequest().setFilterFids(intersects).setSubsetOfAttributes([])
-            for feat in inputLayer.getFeatures(request):
-                tmpGeom = vector.snapToPrecision(feat.geometry(), precision)
+            request = QgsFeatureRequest().setFlags(QgsFeatureRequest.NoGeometry).setFilterRect(bbox).setSubsetOfAttributes([])
+            for test_feat in select_layer.getFeatures(request):
+                if feedback.isCanceled():
+                    break
+
+                if test_feat in selected_set:
+                    # already added this one, no need for further tests
+                    continue
 
-                res = False
                 for predicate in predicates:
                     if predicate == 'disjoint':
-                        if tmpGeom.intersects(geom):
+                        if test_feat.geometry().intersects(f.geometry()):
                             try:
-                                disjoinSet.remove(feat.id())
+                                disjoint_set.remove(test_feat.id())
                             except:
                                 pass  # already removed
                     else:
-                        res = getattr(tmpGeom, predicate)(geom)
-                        if res:
-                            selectedSet.append(feat.id())
+                        if getattr(engine, predicate)(test_feat.geometry().geometry()):
+                            selected_set.add(test_feat.id())
                             break
 
             feedback.setProgress(int(current * total))
 
         if 'disjoint' in predicates:
-            selectedSet = selectedSet + disjoinSet
-
-        if method == 1:
-            selectedSet = list(oldSelection.union(selectedSet))
-        elif method == 2:
-            selectedSet = list(oldSelection.difference(selectedSet))
+            selected_set = list(selected_set) + disjoint_set
 
-        inputLayer.selectByIds(selectedSet)
-        self.setOutputValue(self.OUTPUT, filename)
+        select_layer.selectByIds(list(selected_set), method)
+        return {self.OUTPUT: parameters[self.INPUT]}