Fix normalising constant in quartic kernel

nyalldawson · nyalldawson · commit fd8a02879692 · 2025-02-17T15:38:14.000+10:00
Fixes qgis#60616
diff --git a/src/analysis/raster/qgskde.cpp b/src/analysis/raster/qgskde.cpp
@@ -315,7 +315,7 @@ double QgsKernelDensityEstimation::quarticKernel( const double distance, const d
     case OutputScaled:
     {
       // Normalizing constant
-      const double k = 116. / ( 5. * M_PI * std::pow( bandwidth, 2 ) );
+      const double k = 16. / ( 5. * M_PI * std::pow( bandwidth, 2 ) );
 
       // Derived from Wand and Jones (1995), p. 175
       return k * ( 15. / 16. ) * std::pow( 1. - std::pow( distance / bandwidth, 2 ), 2 );

Original file line number	Diff line number	Diff line change
`@@ -315,7 +315,7 @@ double QgsKernelDensityEstimation::quarticKernel( const double distance, const d`
`315`	`315`	`case OutputScaled:`
`316`	`316`	`{`
`317`	`317`	`// Normalizing constant`
`318`		`- const double k = 116. / ( 5. * M_PI * std::pow( bandwidth, 2 ) );`
	`318`	`+ const double k = 16. / ( 5. * M_PI * std::pow( bandwidth, 2 ) );`
`319`	`319`
`320`	`320`	`// Derived from Wand and Jones (1995), p. 175`
`321`	`321`	`return k * ( 15. / 16. ) * std::pow( 1. - std::pow( distance / bandwidth, 2 ), 2 );`