[gdal-dev] Generating Cloud Optimized GeoTIFFs

[Even Rouault]

On mardi 29 août 2017 09:27:33 CEST daunnc wrote:
> Hi everybody! We're implementing COGs support in GeoTrellis, and there is
> appeared a question related to cloud optimized geotiff definition.
> 
> Following  this <https://trac.osgeo.org/gdal/wiki/CloudOptimizedGeoTIFF>
> page:
> 
> // in.tif is some random tiff.
> 
> 1. gdaladdo in.tif 2 4 8 16 32
> 2. gdal_translate in.tif out.tif -co TILED=YES -co COPY_SRC_OVERVIEWS=YES
> -co COMPRESS=DEFLATE
> 
> After that using  this
> <https://trac.osgeo.org/gdal/wiki/CloudOptimizedGeoTIFF#HowtocheckifaGeoTIFF
> hasacloudoptimizationinternalorganization> python script decided to validate
> the result and was confused by missing IFD_OFFSET tag.

confused ? Can you report the exact error ?

IFD_OFFSET should always be reported for any (valid) TIFF, be it COG or not. This is the offset 
in the file of the image directory, and we must check that it is right at the beginning of the 
file for efficient reading.

I suspect some issue with your setup, although I'm not clear which one. I'd have said perhaps 
you'd run the script against an older GDAL version, but the script does version checking..
To debug this you could try setting a breakpoint in GTiffRasterBand::GetMetadataItem and 
check what happens.

> Can BigTiffs be cloud optimized and can / should BigTiff
> have an offset == 8 as well (16 is a usual offset for them)? 

You're absolutely right. I've just fixed the script to accept those.

Even

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