[gdal-dev] Write overviews directly to S3

[Even Rouault]

Hi Jeremy,

> 
> Is is possible to directly write external overview to a S3 bucket? With GDAL
> 2.1.2 I get an error reporting that seek is not supported when writing to
> vsis3:

No, /vsis3/ only supports sequential writing in files (the original use case was to generate and 
upload a huge CSV file on the fly). I don't have all the details in mind but random writing 
might not be possible given the S3 API constraints, at least with the multipart upload API 
which is used currently.

And another constraint of the current implementation is that a /vsis3/ file is either read-only 
or write-only, but not a mix of both, which would be needed for gdaladdo internal overviews. 
Perhaps external overview would work, but I'm not completely sure as creating a TIFF file 
might require seeking.

Perhaps a fully fledged read-write-update file system would be possible, but that wasn't in 
my initial design constraints.

Even

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