optimize varianceFromCellValues()

qgis · Jul 2, 2020 · 294ad08 · 294ad08
1 parent cf6e634
commit 294ad08
Showing 1 changed file with 7 additions and 1 deletion.
diff --git a/src/analysis/processing/qgsrasteranalysisutils.cpp b/src/analysis/processing/qgsrasteranalysisutils.cpp
@@ -348,7 +348,13 @@ double QgsRasterAnalysisUtils::stddevFromCellValues( std::vector<double> cellVal
 
 double QgsRasterAnalysisUtils::varianceFromCellValues( std::vector<double> cellValues, int stackSize )
 {
-  double variance = std::pow( stddevFromCellValues( cellValues, stackSize ), 2.0 );
+  double mean = meanFromCellValues( cellValues, stackSize );
+  double accum = 0.0;
+  for ( int i = 0; i < stackSize; i++ )
+  {
+    accum += std::pow( ( cellValues.at( i ) - mean ), 2.0 );
+  }
+  double variance = accum / static_cast<double>( stackSize );
   return variance;
 }