[gdal-dev] Generating Cloud Optimized GeoTIFFs

[daunnc]

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#HowtocheckifaGeoTIFFhasacloudoptimizationinternalorganization>  
python script decided to validate the result and was confused by missing
IFD_OFFSET tag.

So the questions are: Should it be present? Is it possible point me to the
GDAL code base, to the place where it can or should be set? Should it be
defined manually? Can BigTiffs be cloud optimized and can / should BigTiff
have an offset == 8 as well (16 is a usual offset for them)? I discovered 
this
<https://github.com/OSGeo/gdal/blob/77544764f51420e42468641fc3d5a087f8ea6d8f/gdal/frmts/gtiff/libtiff/tiff.h#L142>  
link, but still confused about IFD_OFFSET tag necessity / requirement.

GDAL version: GDAL 2.2.1, released 2017/06/23, mac os sierra.



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