[gdal-dev] Creating Cloud Optimized GeoTIFFs

[Even Rouault]

On mercredi 10 mai 2017 14:41:44 CEST Peter Schmitt wrote:
> Hi,
> 
> I ran into something confusing when using gdal-2.2.0 to generate Cloud
> Optimized GeoTIFFs following the instructions at:
> https://trac.osgeo.org/gdal/wiki/CloudOptimizedGeoTIFF
> 
> Here's what I did:
> 
> 1. Fetch an image:
> env CPL_VSIL_CURL_ALLOWED_EXTENSIONS=tif 
GDAL_DISABLE_READDIR_ON_OPEN=YES
> VSI_CACHE=TRUE gdal_translate
> https://github.com/mapbox/rasterio/raw/master/tests/data/RGB.byte.tif
> rgb_byte_jpg.tif -co TILED=YES -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR
> 
> Not a cloud-optimized GeoTIFF as expected:
> 
> validate_cloud_optimized_geotiff.py  rgb_byte_jpg.tif
> rgb_byte_jpg.tif is NOT a valid cloud optimized GeoTIFF : The file should
> have overviews
> 
> 
> 2. Add internal overviews:
> gdaladdo -r average rgb_byte_jpg.tif 2 4 8 16 32
> 
> validate_cloud_optimized_geotiff.py  rgb_byte_jpg.tif
> 
> rgb_byte_jpg.tif is NOT a valid cloud optimized GeoTIFF : The offset of the
> first block of overview of index 3 should be after the one of the overview
> of index 4
> 
> 
> 3.  Translate the image again copying source overviews added above.
> 
> gdal_translate rgb_byte_jpg.tif rgb_byte_jpg_trans.tif -co TILED=YES -co
> COMPRESS=JPEG -co PHOTOMETRIC=YCBCR -co COPY_SRC_OVERVIEWS=YES
> 
> Now the image _is_ cloud-optimized.
> 
> validate_cloud_optimized_geotiff.py  rgb_byte_jpg_trans.tif
> rgb_byte_jpg_trans.tif is a valid cloud optimized GeoTIFF
> 
> 
> I expected the image to be "cloud optimized" at step 2.  Why do I need an
> additional translate?

Peter,

Because gdaladdo will add the overview IFD at the end of the file, whereas in the definition 
of cloud optimized GeoTIFF, they must be all at the beginning of the file so as to be 
efficiently fetchable. And that can only be done with gdal_translate  -co 
COPY_SRC_OVERVIEWS=YES
To avoid quality loss you should only use JPEG compression for the final gdal_translate stage.

Even



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