More efficient distance to vertex calculation in extract nodes alg

Instead of calculating the whole distance from the start of the geometry to the vertex for EVERY vertex, we just keep a running sum of the cumulative distance so far and add the length of each segment as we go. Stats: Before: - dataset 1: > 20 minutes, still going at 14%.... - dataset 2: 92 seconds After: - dataset 1: 3 seconds - dataset 2: 1.7 seconds BAM!
qgis · Nov 14, 2017 · d14b859 · d14b859
1 parent fc6c69b
commit d14b859
Showing 1 changed file with 6 additions and 3 deletions.
diff --git a/src/analysis/processing/qgsalgorithmextractnodes.cpp b/src/analysis/processing/qgsalgorithmextractnodes.cpp
@@ -107,23 +107,26 @@ QVariantMap QgsExtractNodesAlgorithm::processAlgorithm( const QVariantMap &param
     else
     {
       QgsAbstractGeometry::vertex_iterator vi = inputGeom.constGet()->vertices_begin();
-      QgsPoint vertex;
+      double cumulativeDistance = 0.0;
       int vertexPos = 0;
       while ( vi != inputGeom.constGet()->vertices_end() )
       {
         QgsVertexId vertexId = vi.vertexId();
-        double distance = QgsGeometryUtils::distanceToVertex( *( inputGeom.constGet() ), vertexId );
         double angle = inputGeom.constGet()->vertexAngle( vertexId ) * 180 / M_PI;
         QgsAttributes attrs = f.attributes();
         attrs << vertexPos
-              << distance
+              << cumulativeDistance
               << angle;
         QgsFeature outputFeature = QgsFeature();
         outputFeature.setAttributes( attrs );
         outputFeature.setGeometry( QgsGeometry( ( *vi ).clone() ) );
         sink->addFeature( outputFeature, QgsFeatureSink::FastInsert );
         vi++;
         vertexPos++;
+
+        // calculate distance to next vertex
+        double distanceToNext = inputGeom.constGet()->segmentLength( vertexId );
+        cumulativeDistance += distanceToNext;
       }
     }
     feedback->setProgress( i * step );