[processing] Use correct ellipsoid for network analysis tools

Use the processing context's ellipsoid instead of a hardcoded
WGS84 ellipsoid for distance calculations during network
analysis, so that the lengths used will exactly match other
measurement tools used on the same features in the same
project.

python/plugins/processing/tests/testdata/qgis_algorithm_tests2.yaml

@@ -1808,6 +1808,7 @@ tests:
 
   - algorithm: native:shortestpathpointtopoint
     name: Shortest path (point to point, shortest route)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 5.0
@@ -1838,6 +1839,7 @@ tests:
 
   - algorithm: native:shortestpathpointtopoint
     name: Shortest path (point to point, fastest route)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 5.0
@@ -1869,6 +1871,7 @@ tests:
 
   - algorithm: native:shortestpathlayertopoint
     name: Shortest path layer to point
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 5.0
@@ -1899,6 +1902,7 @@ tests:
 
   - algorithm: native:shortestpathpointtolayer
     name: Shortest path point to layer
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 5.0
@@ -1929,6 +1933,7 @@ tests:
 
   - algorithm: native:serviceareafrompoint
     name: Service area from point (shortest, nodes)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -1960,6 +1965,7 @@ tests:
 
   - algorithm: native:serviceareafrompoint
     name: Service area from point (shortest, nodes, bounds)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -1986,6 +1992,7 @@ tests:
 
   - algorithm: native:serviceareafrompoint
     name: Service area from point (shortest, lines)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -2017,6 +2024,7 @@ tests:
 
   - algorithm: native:serviceareafrompoint
     name: Service area from point (fastest, old parameter)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -2051,6 +2059,7 @@ tests:
 
   - algorithm: native:serviceareafrompoint
     name: Service area from point (fastest, new parameter)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -2085,6 +2094,7 @@ tests:
 
   - algorithm: native:serviceareafromlayer
     name: Service area from layer (shortest, nodes)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -2120,6 +2130,7 @@ tests:
 
   - algorithm: native:serviceareafromlayer
     name: Service area from layer (shortest, nodes, boundary)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0
@@ -2147,6 +2158,7 @@ tests:
 
   - algorithm: native:serviceareafromlayer
     name: Service area from layer (shortest, lines)
+    ellipsoid: WGS84
     params:
       DEFAULT_DIRECTION: 2
       DEFAULT_SPEED: 50.0

src/analysis/processing/qgsalgorithmnetworkanalysisbase.cpp

@@ -133,7 +133,7 @@ void QgsNetworkAnalysisAlgorithmBase::loadCommonParams( const QVariantMap &param
     mDirector->addStrategy( new QgsNetworkDistanceStrategy() );
   }
 
-  mBuilder = std::make_unique< QgsGraphBuilder >( mNetwork->sourceCrs(), true, tolerance );
+  mBuilder = std::make_unique< QgsGraphBuilder >( mNetwork->sourceCrs(), true, tolerance, context.ellipsoid() );
 }
 
 void QgsNetworkAnalysisAlgorithmBase::loadPoints( QgsFeatureSource *source, QVector< QgsPointXY > &points, QHash< int, QgsAttributes > &attributes, QgsProcessingContext &context, QgsProcessingFeedback *feedback )