reordering ok with gdal_translate

rename_bands_algorithm.py

@@ -38,6 +38,7 @@ from qgis.core import (QgsProcessing,
                        QgsProcessingParameterBand,
                        QgsProcessingParameterRasterDestination)
 import processing
+import subprocess
 from osgeo import gdal
 
 
@@ -81,6 +82,15 @@ class RenameBandsAlgorithm(QgsProcessingAlgorithm):
                 defaultValue=[None,None]
             )
         )
+            
+        # output raster layer
+        self.addParameter(
+            QgsProcessingParameterRasterDestination(
+                'OUTPUT',
+                self.tr('Raster output')
+            )
+        )
+
 
 
     def processAlgorithm(self, parameters, context, feedback):
@@ -88,40 +98,65 @@ class RenameBandsAlgorithm(QgsProcessingAlgorithm):
         Here is where the processing itself takes place.
         """
 
-        # Retrieve inputs and outputs
+        # RETRIEVE INPUTS AND OUTPUT
         input_raster = self.parameterAsRasterLayer(parameters, self.INPUT, context)
         band_table = self.parameterAsMatrix(parameters, self.TABLE, context)
+        output_raster_path = self.parameterAsOutputLayer(parameters, self.OUTPUT, context)
+        
+        # GETTING USEFUL PAREMETERS
         
         # number of columns in table is used later on, change it here if necessary
         nb_col = 2
+        # index of column used for band order
+        index_bandorder = 1
+        # index of column used for band description
+        index_banddesc = 0
         
+        # transform band_table in a nested list, with 1 element per band, and name and order of each band
+        # [['band 1', 1], ['band 2', 2], ['band 3', 3]]
+        band_table = [band_table[n:n+nb_col] for n in range(0, len(band_table), nb_col)]
         # get input raster path
-        raster_path = input_raster.source()
+        input_raster_path = input_raster.source()
         # read raster with gdal
-        raster_gdal = gdal.Open(raster_path)
-        # get number of bands
-        nbands = raster_gdal.RasterCount
+        input_raster = gdal.Open(input_raster_path)
+        
+        
+        # REORDERING BANDS
+        
+        # get order of bands as a list, i.e. [3,2,1]
+        band_order = [i[index_bandorder] for i in band_table]
+        # reordering bands using gdal_translate
+        kwargs = {
+                'bandList': band_order
+                }
+        output_raster = gdal.Translate(output_raster_path, input_raster_path, **kwargs)
+        
+        
+        # RENAMING BANDS
+        
+        # get number of bands of input raster
+        nbands = input_raster.RasterCount
         # get number of rows in table
-        nrows = len(band_table) / nb_col
+        nrows = len(band_table)
         # check if band number = row count in band_table
         if nbands != nrows:
             message = 'Number of rows in table is different from number of bands in input raster'
             feedback.reportError(QCoreApplication.translate('Rename bands', message))
             return{}
-            
-        # transform band_table in a nested list, with 1 element per band, and name and order of each band
-        # [['band 1', 1], ['band 2', 2], ['band 3', 3]]
-        band_table = [band_table[n:n+nb_col] for n in range(0, len(band_table), nb_col)]
+        
+        # reorder band table so that bands are in same order as in output raster
+        sorted_band_table = sorted(band_table, key = lambda x: x[index_bandorder])
         
         # iterate over each band to set its description using table input
         for band_number in range(nbands):
-            band = raster_gdal.GetRasterBand(band_number + 1)
-            band.SetDescription(band_table[band_number][0])
+            band = output_raster.GetRasterBand(band_number + 1)
+            band.SetDescription(sorted_band_table[band_number][index_banddesc])
+            
             
-        # set band order using table input
+        # RETURNING RESULTS
 
         # Return the results of the algorithm as a dictionary
-        return {}
+        return {self.OUTPUT: output_raster_path}
 
     def name(self):
         """