[gdal-dev] Call for discussion on RFC 63 : Sparse datasets improvements

[Andrew C Aitchison]

On Fri, 8 Jul 2016, Even Rouault wrote:

> The topic of sparse dataset management come back regularly, so I've decided to 
> tackle it.
>
> Please find https://trac.osgeo.org/gdal/wiki/rfc63_sparse_datasets_improvements 
> for review.

I know of several proprietary file formats where the data is tiled
with the index indicating (perhaps implicitly) where the tile has no 
data.

A driver for such formats could have IReadBlock quickly return with
a code to indicate NoData, rather than filling in the image data.
As it stands that might mean extending CPLErr, but would
that be helpful to the main library ?

Is this what is described by having the offset and byte count both zero ?

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I don't really understand how GDAL_DATA_COVERAGE_STATUS values combine
or when pdfDataPct is valid.

In one of the formats above, the tile index has special values
for "no data" and and for "data exists and could be retrieved/purchased
if required". I'd consider mapping these to GDAL_DATA_COVERAGE_STATUS_EMPTY
and GDAL_DATA_COVERAGE_STATUS_UNIMPLEMENTED. Does that make sense ?

-- 
Andrew C Aitchison