-echo Now create the VRT and external overview layers
-echo 1: gdalbuildvrt -resolution highest -hidenodata diffXYZ.vrt diff/*.tif
-echo 2: gdaladdo --config GDAL_CACHEMAX=16000 -ro --config COMPRESS DEFLATE --config COMPRESS_OVERVIEW DEFLATE --config ZLEVEL 9 --config BIGTIFF_OVERVIEW IF_SAFER --config GDAL_TIFF_OVR_BLOCKSIZE 512 -r average ossv-2016-04-combined.vrt 4 16 64 256 1024 4096
+echo Now create external overview layers
+echo eg: gdaladdo --config GDAL_CACHEMAX=16000 -ro --config COMPRESS DEFLATE --config COMPRESS_OVERVIEW DEFLATE --config ZLEVEL 9 --config BIGTIFF_OVERVIEW IF_SAFER --config GDAL_TIFF_OVR_BLOCKSIZE 512 -r average ossv-2016-04-combined.vrt 4 16 64 256 1024 4096