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

jramm jamessramm at gmail.com
Sun Jul 10 02:07:00 PDT 2016

Even Rouault-2 wrote
> For GeoTIFF, the unit of query remains the block. So if a block is missing
> is 
> present, it computes how many pixels of the window of request intersect
> the 
> block, and count them as present.
> Imagine that you have a raster of dimensions 20x20, with tiles of size
> 10x10. 
> Imagine the first block (pixels 0,0 to 9,9) is missing. And you call 
> GetDataCoverageStatus() with (5,5,15,15). Then you will have a
> contribution of 
> 10x5 valid pixels from the top-right block, 5x10 from the bottom-left
> block 
> and 10x10 from the bottom-right block, hence a non-null percentage of 200.
> / 
> 225. * 100 = 88.9 %

Ah ok, makes sense. 
Having SPARSE_OK=YES mean that gdal_translate will actually skip null blocks
is a good additiona also - more intuitive. 

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