[processing] Fix Distance Matrix alg considers distances to

same points

Add more unit tests

Fixes #17350

(cherry-picked from 7fa9d41)

Author: nyalldawson

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

@@ -111,6 +111,7 @@ def processAlgorithm(self, parameters, context, feedback):
         source_field = self.parameterAsString(parameters, self.INPUT_FIELD, context)
         target_source = self.parameterAsSource(parameters, self.TARGET, context)
         target_field = self.parameterAsString(parameters, self.TARGET_FIELD, context)
+        same_source_and_target = parameters[self.INPUT] == parameters[self.TARGET]
         matType = self.parameterAsEnum(parameters, self.MATRIX_TYPE, context)
         nPoints = self.parameterAsInt(parameters, self.NEAREST_POINTS, context)
 
@@ -119,19 +120,25 @@ def processAlgorithm(self, parameters, context, feedback):
 
         if matType == 0:
             # Linear distance matrix
-            return self.linearMatrix(parameters, context, source, source_field, target_source, target_field,
+            return self.linearMatrix(parameters, context, source, source_field, target_source, target_field, same_source_and_target,
                                      matType, nPoints, feedback)
         elif matType == 1:
             # Standard distance matrix
             return self.regularMatrix(parameters, context, source, source_field, target_source, target_field,
                                       nPoints, feedback)
         elif matType == 2:
             # Summary distance matrix
-            return self.linearMatrix(parameters, context, source, source_field, target_source, target_field,
+            return self.linearMatrix(parameters, context, source, source_field, target_source, target_field, same_source_and_target,
                                      matType, nPoints, feedback)
 
-    def linearMatrix(self, parameters, context, source, inField, target_source, targetField,
+    def linearMatrix(self, parameters, context, source, inField, target_source, targetField, same_source_and_target,
                      matType, nPoints, feedback):
+
+        if same_source_and_target:
+            # need to fetch an extra point from the index, since the closest match will always be the same
+            # as the input feature
+            nPoints += 1
+
         inIdx = source.fields().lookupField(inField)
         outIdx = target_source.fields().lookupField(targetField)
 
@@ -176,6 +183,9 @@ def linearMatrix(self, parameters, context, source, inField, target_source, targ
                 if feedback.isCanceled():
                     break
 
+                if same_source_and_target and inFeat.id() == outFeat.id():
+                    continue
+
                 outID = outFeat.attributes()[outIdx]
                 outGeom = outFeat.geometry()
                 dist = distArea.measureLine(inGeom.asPoint(),
@@ -207,6 +217,7 @@ def linearMatrix(self, parameters, context, source, inField, target_source, targ
 
     def regularMatrix(self, parameters, context, source, inField, target_source, targetField,
                       nPoints, feedback):
+
         distArea = QgsDistanceArea()
         distArea.setSourceCrs(source.sourceCrs(), context.transformContext())
         distArea.setEllipsoid(context.project().ellipsoid())

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

@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xs:schema targetNamespace="http://ogr.maptools.org/" xmlns:ogr="http://ogr.maptools.org/" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:gml="http://www.opengis.net/gml" elementFormDefault="qualified" version="1.0">
+<xs:import namespace="http://www.opengis.net/gml" schemaLocation="http://schemas.opengis.net/gml/2.1.2/feature.xsd"/>
+<xs:element name="FeatureCollection" type="ogr:FeatureCollectionType" substitutionGroup="gml:_FeatureCollection"/>
+<xs:complexType name="FeatureCollectionType">
+  <xs:complexContent>
+    <xs:extension base="gml:AbstractFeatureCollectionType">
+      <xs:attribute name="lockId" type="xs:string" use="optional"/>
+      <xs:attribute name="scope" type="xs:string" use="optional"/>
+    </xs:extension>
+  </xs:complexContent>
+</xs:complexType>
+<xs:element name="linear_matrix_diff" type="ogr:linear_matrix_diff_Type" substitutionGroup="gml:_Feature"/>
+<xs:complexType name="linear_matrix_diff_Type">
+  <xs:complexContent>
+    <xs:extension base="gml:AbstractFeatureType">
+      <xs:sequence>
+        <xs:element name="geometryProperty" type="gml:MultiPointPropertyType" nillable="true" minOccurs="0" maxOccurs="1"/>
+        <xs:element name="InputID" nillable="true" minOccurs="0" maxOccurs="1">
+          <xs:simpleType>
+            <xs:restriction base="xs:string">
+              <xs:maxLength value="255"/>
+            </xs:restriction>
+          </xs:simpleType>
+        </xs:element>
+        <xs:element name="TargetID" nillable="true" minOccurs="0" maxOccurs="1">
+          <xs:simpleType>
+            <xs:restriction base="xs:string">
+              <xs:maxLength value="255"/>
+            </xs:restriction>
+          </xs:simpleType>
+        </xs:element>
+        <xs:element name="Distance" nillable="true" minOccurs="0" maxOccurs="1">
+          <xs:simpleType>
+            <xs:restriction base="xs:decimal">
+            </xs:restriction>
+          </xs:simpleType>
+        </xs:element>
+      </xs:sequence>
+    </xs:extension>
+  </xs:complexContent>
+</xs:complexType>
+</xs:schema>