text: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  # *****************************************************************************
  #  $Id$
  #
  #  Project:  GDAL
  #  Purpose:  Validate Cloud Optimized GeoTIFF file structure
  #  Author:   Even Rouault, <even dot rouault at spatialys dot com>
  #
  # *****************************************************************************
  #  Copyright (c) 2017, Even Rouault
  #
  #  Permission is hereby granted, free of charge, to any person obtaining a
  #  copy of this software and associated documentation files (the "Software"),
  #  to deal in the Software without restriction, including without limitation
  #  the rights to use, copy, modify, merge, publish, distribute, sublicense,
  #  and/or sell copies of the Software, and to permit persons to whom the
  #  Software is furnished to do so, subject to the following conditions:
  #
  #  The above copyright notice and this permission notice shall be included
  #  in all copies or substantial portions of the Software.
  #
  #  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  #  OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  #  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  #  THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  #  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  #  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  #  DEALINGS IN THE SOFTWARE.
  # *****************************************************************************
  
  import sys
  from osgeo import gdal
  
  
  def Usage():
      print("Usage: validate_cloud_optimized_geotiff.py [-q] test.tif")
      print("")
      return 1
  
  
  class ValidateCloudOptimizedGeoTIFFException(Exception):
      pass
  
  
  def validate(ds, check_tiled=True):
      """Check if a file is a (Geo)TIFF with cloud optimized compatible structure.
  
      Args:
        ds: GDAL Dataset for the file to inspect.
        check_tiled: Set to False to ignore missing tiling.
  
      Returns:
        A tuple, whose first element is an array of error messages
        (empty if there is no error), and the second element, a dictionary
        with the structure of the GeoTIFF file.
  
      Raises:
        ValidateCloudOptimizedGeoTIFFException: Unable to open the file or the
          file is not a Tiff.
      """
  
      if int(gdal.VersionInfo("VERSION_NUM")) < 2020000:
          raise ValidateCloudOptimizedGeoTIFFException("GDAL 2.2 or above required")
  
      unicode_type = type("".encode("utf-8").decode("utf-8"))
      if isinstance(ds, (str, unicode_type)):
          gdal.PushErrorHandler()
          ds = gdal.Open(ds)
          gdal.PopErrorHandler()
          if ds is None:
              raise ValidateCloudOptimizedGeoTIFFException(
                  "Invalid file : %s" % gdal.GetLastErrorMsg()
              )
          if ds.GetDriver().ShortName != "GTiff":
              raise ValidateCloudOptimizedGeoTIFFException("The file is not a GeoTIFF")
  
      details = {}
      errors = []
      filename = ds.GetDescription()
      main_band = ds.GetRasterBand(1)
      ovr_count = main_band.GetOverviewCount()
      filelist = ds.GetFileList()
      if filelist is not None and filename + ".ovr" in filelist:
          errors += ["Overviews found in external .ovr file. They should be internal"]
  
      if main_band.XSize >= 512 or main_band.YSize >= 512:
          if check_tiled:
              block_size = main_band.GetBlockSize()
              if block_size[0] == main_band.XSize and block_size[0] > 1024:
                  errors += ["The file is greater than 512xH or Wx512, but is not tiled"]
  
          if ovr_count == 0:
              errors += ["The file is greater than 512xH or Wx512, but has no overviews"]
  
      ifd_offset = int(main_band.GetMetadataItem("IFD_OFFSET", "TIFF"))
      ifd_offsets = [ifd_offset]
      if ifd_offset not in (8, 16):
          errors += [
              "The offset of the main IFD should be 8 for ClassicTIFF "
              "or 16 for BigTIFF. It is %d instead" % ifd_offsets[0]
          ]
      details["ifd_offsets"] = {}
      details["ifd_offsets"]["main"] = ifd_offset
  
      for i in range(ovr_count):
          # Check that overviews are by descending sizes
          ovr_band = ds.GetRasterBand(1).GetOverview(i)
          if i == 0:
              if ovr_band.XSize > main_band.XSize or ovr_band.YSize > main_band.YSize:
                  errors += ["First overview has larger dimension than main band"]
          else:
              prev_ovr_band = ds.GetRasterBand(1).GetOverview(i - 1)
              if (
                  ovr_band.XSize > prev_ovr_band.XSize
                  or ovr_band.YSize > prev_ovr_band.YSize
              ):
                  errors += [
                      "Overview of index %d has larger dimension than "
                      "overview of index %d" % (i, i - 1)
                  ]
  
          if check_tiled:
              block_size = ovr_band.GetBlockSize()
              if block_size[0] == ovr_band.XSize and block_size[0] > 1024:
                  errors += ["Overview of index %d is not tiled" % i]
  
          # Check that the IFD of descending overviews are sorted by increasing
          # offsets
          ifd_offset = int(ovr_band.GetMetadataItem("IFD_OFFSET", "TIFF"))
          ifd_offsets.append(ifd_offset)
          details["ifd_offsets"]["overview_%d" % i] = ifd_offset
          if ifd_offsets[-1] < ifd_offsets[-2]:
              if i == 0:
                  errors += [
                      "The offset of the IFD for overview of index %d is %d, "
                      "whereas it should be greater than the one of the main "
                      "image, which is at byte %d" % (i, ifd_offsets[-1], ifd_offsets[-2])
                  ]
              else:
                  errors += [
                      "The offset of the IFD for overview of index %d is %d, "
                      "whereas it should be greater than the one of index %d, "
                      "which is at byte %d" % (i, ifd_offsets[-1], i - 1, ifd_offsets[-2])
                  ]
  
      # Check that the imagery starts by the smallest overview and ends with
      # the main resolution dataset
      block_offset = main_band.GetMetadataItem("BLOCK_OFFSET_0_0", "TIFF")
      if not block_offset:
          errors += ["Missing BLOCK_OFFSET_0_0"]
      data_offset = int(block_offset) if block_offset else None
      data_offsets = [data_offset]
      details["data_offsets"] = {}
      details["data_offsets"]["main"] = data_offset
      for i in range(ovr_count):
          ovr_band = ds.GetRasterBand(1).GetOverview(i)
          data_offset = int(ovr_band.GetMetadataItem("BLOCK_OFFSET_0_0", "TIFF"))
          data_offsets.append(data_offset)
          details["data_offsets"]["overview_%d" % i] = data_offset
  
      if data_offsets[-1] < ifd_offsets[-1]:
          if ovr_count > 0:
              errors += [
                  "The offset of the first block of the smallest overview "
                  "should be after its IFD"
              ]
          else:
              errors += [
                  "The offset of the first block of the image should " "be after its IFD"
              ]
      for i in range(len(data_offsets) - 2, 0, -1):
          if data_offsets[i] < data_offsets[i + 1]:
              errors += [
                  "The offset of the first block of overview of index %d should "
                  "be after the one of the overview of index %d" % (i - 1, i)
              ]
      if len(data_offsets) >= 2 and data_offsets[0] < data_offsets[1]:
          errors += [
              "The offset of the first block of the main resolution image"
              "should be after the one of the overview of index %d" % (ovr_count - 1)
          ]
  
      return errors, details
  
  
  def main():
      """Return 0 in case of success, 1 for failure."""
  
      i = 1
      filename = None
      quiet = False
      while i < len(sys.argv):
          if sys.argv[i] == "-q":
              quiet = True
          elif sys.argv[i][0] == "-":
              return Usage()
          elif filename is None:
              filename = sys.argv[i]
          else:
              return Usage()
  
          i += 1
  
      if filename is None:
          return Usage()
  
      try:
          errors, _ = validate(filename)
          if errors:
              if not quiet:
                  print("%s is NOT a valid cloud optimized GeoTIFF." % filename)
                  print("The following errors were found:")
                  for error in errors:
                      print(" - " + error)
              ret = 1
          else:
              ret = 0
              if not quiet:
                  print("%s is a valid cloud optimized GeoTIFF" % filename)
      except ValidateCloudOptimizedGeoTIFFException as e:
          if not quiet:
              print("%s is NOT a valid cloud optimized GeoTIFF : %s" % (filename, str(e)))
          ret = 1
  
      return ret
  
  
  if __name__ == "__main__":
      sys.exit(main())
  