NormalizeData#add_alpha_channel: use compression option when calling …

…gdalwarp

ref #789
ref #802

uses a more circuitous way of adding alpha channel (gdalwarp to add alpha channel and output to vrt, then pipe that to gdal_translate for compression).  this provides better compression and faster computation than solely using gdalwarp.

lib/gis_robot_suite/raster_normalizer.rb

@@ -23,6 +23,7 @@ def normalize
 
       epsg4326_projection? ? compress_only : reproject_and_compress
       convert_8bit_to_rgb if eight_bit?
+      add_alpha_channel
       compute_statistics
       tmpdir
     end
@@ -77,6 +78,28 @@ def convert_8bit_to_rgb
       File.delete(temp_filename)
     end
 
+    def add_alpha_channel
+      # NOTE: gdalwarp is smart enough not to add a new alpha channel (band) if one is already there.
+      # If we want to improve the performance of the normalize step, and many GeoTIFFs already
+      # have alpha channels, then we could introspect on the GeoTIFF file with gdalinfo and skip
+      # this call to gdalwarp if one is already present.
+
+      # NOTE: the roundabout approach of outputting the alpha channel add to a vrt, and piping that
+      # gdalwarp result to gdal_translate to create an actual compressed tif is an attempt to workaround
+      # a known issue with the compression option being provided directly to gdalwarp.  See:
+      #   https://trac.osgeo.org/gdal/wiki/UserDocs/GdalWarp#GeoTIFFoutput-coCOMPRESSisbroken
+      #   https://gdal.org/programs/gdalwarp.html#compressed-output
+      #   https://gdal.org/user/virtual_file_systems.html#vsistdout-standard-output-streaming
+      #   https://gis.stackexchange.com/questions/89444/file-size-inflation-normal-with-gdalwarp
+
+      logger.info "load-raster: adding alpha channel for #{output_filepath}"
+      temp_filepath = "#{tmpdir}/#{geo_object_name}_alpha.tif"
+      gdalwarp_cmd = "#{Settings.gdal_path}gdalwarp -dstalpha -of vrt #{output_filepath} /vsistdout/"
+      gdal_translate_cmd = "#{Settings.gdal_path}gdal_translate -co 'compress=LZW' /vsistdin/ #{temp_filepath}"
+      Kernel.system("#{gdalwarp_cmd} | #{gdal_translate_cmd}", exception: true)
+      FileUtils.mv(temp_filepath, output_filepath)
+    end
+
     def compute_statistics
       Kernel.system("#{Settings.gdal_path}gdalinfo -mm -stats -norat -noct #{output_filepath}", exception: true)
     end

spec/gis_robot_suite/raster_normalizer_spec.rb

@@ -116,6 +116,11 @@
           "gdal_translate -expand rgb /tmp/normalizeraster_bb021mm7809/raw8bit.tif /tmp/normalizeraster_bb021mm7809/MCE_FI2G_2014.tif -co 'COMPRESS=LZW'",
           exception: true
         )
+        # Adds an alpha channel
+        expect(Kernel).to have_received(:system).with(
+          "gdalwarp -dstalpha -of vrt /tmp/normalizeraster_bb021mm7809/MCE_FI2G_2014.tif /vsistdout/ | gdal_translate -co 'compress=LZW' /vsistdin/ /tmp/normalizeraster_bb021mm7809/MCE_FI2G_2014_alpha.tif", # rubocop:disable Layout/LineLength
+          exception: true
+        )
         # Stats
         expect(Kernel).to have_received(:system).with(
           'gdalinfo -mm -stats -norat -noct /tmp/normalizeraster_bb021mm7809/MCE_FI2G_2014.tif',