[FEATURE] Snap to layer algorithm accepts a mode parameter

With a new option to prefer to snap to closest point on geometry.
The old behaviour was to prefer to snap to nodes, even if a node
was further from the input geometry than a segment. The new option
allows you to snap geometries to the closest point, regardless
of whether it's a node or segment.

python/analysis/vector/qgsgeometrysnapper.sip

@@ -15,26 +15,33 @@ class QgsGeometrySnapper : QObject
 
   public:
 
+    //! Snapping modes
+    enum SnapMode
+    {
+      PreferNodes, //!< Prefer to snap to nodes, even when a segment may be closer than a node
+      PreferClosest, //!< Snap to closest point, regardless of it is a node or a segment
+    };
+
     /**
      * Constructor for QgsGeometrySnapper. A reference layer which contains geometries to snap to must be
-     * set. The snap tolerance is specified in the layer units for the
-     * reference layer, and it is assumed that all geometries snapped using this object will have the
+     * set. It is assumed that all geometries snapped using this object will have the
      * same CRS as the reference layer (ie, no reprojection is performed).
      */
-    QgsGeometrySnapper( QgsVectorLayer* referenceLayer, double snapTolerance );
+    QgsGeometrySnapper( QgsVectorLayer* referenceLayer );
 
     /**
      * Snaps a geometry to the reference layer and returns the result. The geometry must be in the same
-     * CRS as the reference layer.
+     * CRS as the reference layer, and must have the same type as the reference layer geometry. The snap tolerance
+     * is specified in the layer units for the reference layer.
      */
-    QgsGeometry snapGeometry( const QgsGeometry& geometry ) const;
+    QgsGeometry snapGeometry( const QgsGeometry& geometry, double snapTolerance, SnapMode mode = PreferNodes ) const;
 
     /**
      * Snaps a set of features to the reference layer and returns the result. This operation is
      * multithreaded for performance. The featureSnapped() signal will be emitted each time a feature
-     * is processed. This method is not safe to call from multiple threads concurrently.
+     * is processed. The snap tolerance is specified in the layer units for the reference layer.
      */
-    QgsFeatureList snapFeatures( const QgsFeatureList& features );
+    QgsFeatureList snapFeatures( const QgsFeatureList& features, double snapTolerance, SnapMode mode = PreferNodes );
 
   signals:
 

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

@@ -30,7 +30,7 @@
 from qgis.core import QgsFeature
 
 from processing.core.GeoAlgorithm import GeoAlgorithm
-from processing.core.parameters import ParameterVector, ParameterNumber
+from processing.core.parameters import ParameterVector, ParameterNumber, ParameterSelection
 from processing.core.outputs import OutputVector
 from processing.tools import dataobjects, vector
 
@@ -41,6 +41,7 @@ class SnapGeometriesToLayer(GeoAlgorithm):
     REFERENCE_LAYER = 'REFERENCE_LAYER'
     TOLERANCE = 'TOLERANCE'
     OUTPUT = 'OUTPUT'
+    BEHAVIOUR = 'BEHAVIOUR'
 
     def defineCharacteristics(self):
         self.name, self.i18n_name = self.trAlgorithm('Snap geometries to layer')
@@ -49,12 +50,20 @@ def defineCharacteristics(self):
         self.addParameter(ParameterVector(self.INPUT, self.tr('Input layer')))
         self.addParameter(ParameterVector(self.REFERENCE_LAYER, self.tr('Reference layer')))
         self.addParameter(ParameterNumber(self.TOLERANCE, self.tr('Tolerance (layer units)'), 0.00000001, 9999999999, default=10.0))
+
+        self.modes = [self.tr('Prefer aligning nodes'),
+                      self.tr('Prefer closest point')]
+        self.addParameter(ParameterSelection(
+            self.BEHAVIOUR,
+            self.tr('Behaviour'),
+            self.modes, default=0))
         self.addOutput(OutputVector(self.OUTPUT, self.tr('Snapped geometries')))
 
     def processAlgorithm(self, progress):
         layer = dataobjects.getObjectFromUri(self.getParameterValue(self.INPUT))
         reference_layer = dataobjects.getObjectFromUri(self.getParameterValue(self.REFERENCE_LAYER))
         tolerance = self.getParameterValue(self.TOLERANCE)
+        mode = self.getParameterValue(self.BEHAVIOUR)
 
         writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(
             layer.fields(), layer.wkbType(), layer.crs())
@@ -65,9 +74,9 @@ def processAlgorithm(self, progress):
         self.progress = progress
         self.total = 100.0 / len(features)
 
-        snapper = QgsGeometrySnapper(reference_layer, tolerance)
+        snapper = QgsGeometrySnapper(reference_layer)
         snapper.featureSnapped.connect(self.featureSnapped)
-        snapped_features = snapper.snapFeatures(features)
+        snapped_features = snapper.snapFeatures(features, tolerance, mode)
         for f in snapped_features:
             writer.addFeature(QgsFeature(f))
 

python/plugins/processing/tests/testdata/expected/snap_lines_to_lines.gml

@@ -7,13 +7,13 @@
   <gml:boundedBy>
     <gml:Box>
       <gml:coord><gml:X>-1</gml:X><gml:Y>-5</gml:Y></gml:coord>
-      <gml:coord><gml:X>11.34678899082569</gml:X><gml:Y>5.288990825688074</gml:Y></gml:coord>
+      <gml:coord><gml:X>11</gml:X><gml:Y>5</gml:Y></gml:coord>
     </gml:Box>
   </gml:boundedBy>
-
+                                                                                                                                                             
   <gml:featureMember>
     <ogr:snap_lines_to_lines fid="lines.0">
-      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>6,2 9,2 9,3 11,5 11.346788990825686,5.288990825688074</gml:coordinates></gml:LineString></ogr:geometryProperty>
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>6,2 9,2 9,3 11,5</gml:coordinates></gml:LineString></ogr:geometryProperty>
     </ogr:snap_lines_to_lines>
   </gml:featureMember>
   <gml:featureMember>
@@ -23,7 +23,7 @@
   </gml:featureMember>
   <gml:featureMember>
     <ogr:snap_lines_to_lines fid="lines.2">
-      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>2,0 2,2 2,2 3,2 3,2</gml:coordinates></gml:LineString></ogr:geometryProperty>
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>2,0 2,2 2,2 3,2</gml:coordinates></gml:LineString></ogr:geometryProperty>
     </ogr:snap_lines_to_lines>
   </gml:featureMember>
   <gml:featureMember>
@@ -38,7 +38,7 @@
   </gml:featureMember>
   <gml:featureMember>
     <ogr:snap_lines_to_lines fid="lines.5">
-      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>6,-3 10,1 10.208073394495411,0.849724770642202</gml:coordinates></gml:LineString></ogr:geometryProperty>
+      <ogr:geometryProperty><gml:LineString srsName="EPSG:4326"><gml:coordinates>6,-3 10,1</gml:coordinates></gml:LineString></ogr:geometryProperty>
     </ogr:snap_lines_to_lines>
   </gml:featureMember>
   <gml:featureMember>

python/plugins/processing/tests/testdata/expected/snap_point_to_lines_prefer_closest.gfs

@@ -0,0 +1,16 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>snap_point_to_lines_prefer_closest</Name>
+    <ElementPath>snap_point_to_lines_prefer_closest</ElementPath>
+    <!--POINT-->
+    <GeometryType>1</GeometryType>
+    <SRSName>EPSG:4326</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>9</FeatureCount>
+      <ExtentXMin>0.20114</ExtentXMin>
+      <ExtentXMax>7.97127</ExtentXMax>
+      <ExtentYMin>-4.82759</ExtentYMin>
+      <ExtentYMax>2.74139</ExtentYMax>
+    </DatasetSpecificInfo>
+  </GMLFeatureClass>
+</GMLFeatureClassList>

python/plugins/processing/tests/testdata/expected/snap_point_to_lines_prefer_closest.gml

@@ -0,0 +1,59 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ogr:FeatureCollection
+     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+     xsi:schemaLocation=""
+     xmlns:ogr="http://ogr.maptools.org/"
+     xmlns:gml="http://www.opengis.net/gml">
+  <gml:boundedBy>
+    <gml:Box>
+      <gml:coord><gml:X>0.201140250855188</gml:X><gml:Y>-4.827594070695552</gml:Y></gml:coord>
+      <gml:coord><gml:X>7.971265678449257</gml:X><gml:Y>2.74139110604333</gml:Y></gml:coord>
+    </gml:Box>
+  </gml:boundedBy>
+
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_closest fid="points.0">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>1,1</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_closest>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_closest fid="points.1">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>3.0,2.74139110604333</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_closest>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_closest fid="points.2">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>2,2</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_closest>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_closest fid="points.3">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>5,1</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_closest>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_closest fid="points.4">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>3.683922462941847,1.0</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_closest>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_closest fid="points.5">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>0.201140250855188,-4.827594070695552</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_closest>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_closest fid="points.6">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>7.971265678449257,0.609122006841505</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_closest>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_closest fid="points.7">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>7.456898517673889,-1.543101482326111</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_closest>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_closest fid="points.8">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>0.220296465222349,-1.0</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_closest>
+  </gml:featureMember>
+</ogr:FeatureCollection>

python/plugins/processing/tests/testdata/expected/snap_point_to_lines_prefer_nodes.gfs

@@ -0,0 +1,16 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>snap_point_to_lines_prefer_nodes</Name>
+    <ElementPath>snap_point_to_lines_prefer_nodes</ElementPath>
+    <!--POINT-->
+    <GeometryType>1</GeometryType>
+    <SRSName>EPSG:4326</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>9</FeatureCount>
+      <ExtentXMin>0.20114</ExtentXMin>
+      <ExtentXMax>7.97127</ExtentXMax>
+      <ExtentYMin>-4.82759</ExtentYMin>
+      <ExtentYMax>3.00000</ExtentYMax>
+    </DatasetSpecificInfo>
+  </GMLFeatureClass>
+</GMLFeatureClassList>

python/plugins/processing/tests/testdata/expected/snap_point_to_lines_prefer_nodes.gml

@@ -0,0 +1,59 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ogr:FeatureCollection
+     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+     xsi:schemaLocation=""
+     xmlns:ogr="http://ogr.maptools.org/"
+     xmlns:gml="http://www.opengis.net/gml">
+  <gml:boundedBy>
+    <gml:Box>
+      <gml:coord><gml:X>0.201140250855188</gml:X><gml:Y>-4.827594070695552</gml:Y></gml:coord>
+      <gml:coord><gml:X>7.971265678449257</gml:X><gml:Y>3</gml:Y></gml:coord>
+    </gml:Box>
+  </gml:boundedBy>
+
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_nodes fid="points.0">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>1,1</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_nodes>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_nodes fid="points.1">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>3,3</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_nodes>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_nodes fid="points.2">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>2,2</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_nodes>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_nodes fid="points.3">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>5,1</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_nodes>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_nodes fid="points.4">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>3,1</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_nodes>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_nodes fid="points.5">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>0.201140250855188,-4.827594070695552</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_nodes>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_nodes fid="points.6">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>7.971265678449257,0.609122006841505</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_nodes>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_nodes fid="points.7">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>7.456898517673889,-1.543101482326111</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_nodes>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:snap_point_to_lines_prefer_nodes fid="points.8">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:4326"><gml:coordinates>1,-1</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:snap_point_to_lines_prefer_nodes>
+  </gml:featureMember>
+</ogr:FeatureCollection>

python/plugins/processing/tests/testdata/qgis_algorithm_tests.yaml

@@ -1431,4 +1431,36 @@ tests:
     results:
       OUTPUT:
         name: expected/snap_points_to_points.gml
-        type: vector
+        type: vector
+
+  - algorithm: qgis:snapgeometriestolayer
+    name: Snap points to lines (prefer nodes)
+    params:
+      BEHAVIOUR: '0'
+      INPUT:
+        name: snap_points.gml
+        type: vector
+      REFERENCE_LAYER:
+        name: lines.gml
+        type: vector
+      TOLERANCE: 1.0
+    results:
+      OUTPUT:
+        name: expected/snap_point_to_lines_prefer_nodes.gml
+        type: vector
+
+  - algorithm: qgis:snapgeometriestolayer
+    name: Snap points to lines (prefer closest)
+    params:
+      BEHAVIOUR: '1'
+      INPUT:
+        name: snap_points.gml
+        type: vector
+      REFERENCE_LAYER:
+        name: lines.gml
+        type: vector
+      TOLERANCE: 1.0
+    results:
+      OUTPUT:
+        name: expected/snap_point_to_lines_prefer_closest.gml
+        type: vector