[needs-docs][processing] add help and clarity to the define current p…

…rojection algorithm

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

@@ -550,3 +550,9 @@ qgis:voronoipolygons: >
 
 qgis:zonalstatistics:
 
+
+qgis:definecurrentprojection: >
+  This algorithm sets an existing layer's projection to the provided CRS. Contrary to the "Assign projection" algorithm, it will not output a new layer.
+
+  For shapefile datasets, the .prj and .qpj files will be overwritten - or created if missing - to match the provided CRS.
+

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

@@ -56,15 +56,15 @@ def __init__(self):
     def initAlgorithm(self, config=None):
         self.addParameter(QgsProcessingParameterVectorLayer(self.INPUT,
                                                             self.tr('Input Layer'), types=[QgsProcessing.TypeVectorAnyGeometry]))
-        self.addParameter(QgsProcessingParameterCrs(self.CRS, 'Output CRS'))
+        self.addParameter(QgsProcessingParameterCrs(self.CRS, 'CRS'))
         self.addOutput(QgsProcessingOutputVectorLayer(self.INPUT,
                                                       self.tr('Layer with projection')))
 
     def name(self):
         return 'definecurrentprojection'
 
     def displayName(self):
-        return self.tr('Define current projection')
+        return self.tr('Define layer projection')
 
     def flags(self):
         return super().flags() | QgsProcessingAlgorithm.FlagNoThreading
@@ -81,15 +81,17 @@ def processAlgorithm(self, parameters, context, feedback):
         if dsPath.lower().endswith('.shp'):
             dsPath = dsPath[:-4]
 
-        wkt = crs.toWkt()
-        with open(dsPath + '.prj', 'w') as f:
-            f.write(wkt)
-
-        qpjFile = dsPath + '.qpj'
-        if os.path.exists(qpjFile):
-            with open(qpjFile, 'w') as f:
+            wkt = crs.toWkt()
+            with open(dsPath + '.prj', 'w') as f:
                 f.write(wkt)
 
+            qpjFile = dsPath + '.qpj'
+            if os.path.exists(qpjFile):
+                with open(qpjFile, 'w') as f:
+                    f.write(wkt)
+        else:
+            feedback.pushConsoleInfo(tr("Data source isn't a shapefile, skipping .prj/.qpj creation"))
+
         layer.setCrs(crs)
         layer.triggerRepaint()