Apply SLD PointSymbolizer on single centroid for polygon

SLD 1.0 and StyleEncoding 1.1 specs say that if a line, polygon, or raster geometry is used with PointSymbolizer, then the semantic is to use the centroid of the geometry, or any similar representative point.

When QGIS read an SLD, it applies the point on the centroid of all parts of the multi-polygon and not on the unique centroid of the mutil-polygon.

ST_Centroid is the PostGIS implementation of the Simple Feature standard for SQL and it generates only one point for multi-polygon. So I think SLD PointSymbolizer has to be applied to the single centroid.

Author: rldhont

src/core/symbology/qgsfillsymbollayer.cpp

@@ -3512,6 +3512,7 @@ QgsSymbolLayer *QgsCentroidFillSymbolLayer::createFromSld( QDomElement &element
 
   std::unique_ptr< QgsCentroidFillSymbolLayer > sl = qgis::make_unique< QgsCentroidFillSymbolLayer >();
   sl->setSubSymbol( marker.release() );
+  sl->setPointOnAllParts( false );
   return sl.release();
 }