Merge algorithm reprojects layers so that all features are

in CRS of first input layer

Author: nyalldawson

python/plugins/processing/algs/help/qgis.yaml

@@ -314,6 +314,8 @@ qgis:mergevectorlayers: >
 
   If attributes tables are different, the attribute table of the resulting layer will contain the attributes from both input layers.
 
+  The layers will all be reprojected to match the coordinate reference system of the first input layer.
+
 qgis:multiparttosingleparts: >
   This algorithm takes a vector layer with multipart geometries and generates a new one in which all geometries contain a single part. Features with multipart geometries are divided in as many different features as parts the geometry contain, and the same attributes are used for each of them.
 

python/plugins/processing/algs/qgis/Merge.py

@@ -30,6 +30,7 @@
 from qgis.PyQt.QtGui import QIcon
 from qgis.PyQt.QtCore import QVariant
 from qgis.core import (QgsFields,
+                       QgsFeatureRequest,
                        QgsProcessingUtils,
                        QgsProcessingParameterMultipleLayers,
                        QgsProcessingParameterDefinition,
@@ -104,12 +105,13 @@ def processAlgorithm(self, parameters, context, feedback):
                     fields.append(sfield)
 
         total = 100.0 / totalFeatureCount
+        dest_crs = layers[0].crs()
         (sink, dest_id) = self.parameterAsSink(parameters, self.OUTPUT, context,
-                                               fields, layers[0].wkbType(), layers[0].crs())
+                                               fields, layers[0].wkbType(), dest_crs)
 
         featureCount = 0
         for layer in layers:
-            for feature in layer.getFeatures():
+            for feature in layer.getFeatures(QgsFeatureRequest().setDestinationCrs(dest_crs)):
                 if feedback.isCanceled():
                     break