[Gdal-dev] Nodata bitmasks / null processing

[Frank Warmerdam]

Ray Gardener wrote:
> Frank Warmerdam wrote:
>> That is a possibility though I hadn't actually considered it previously.
>> A whole bitmask won't go in the .aux.xml file though, so it does make
>> things substantially more involved as some sort of additional data file
>> would be required.
> 
> Would you make an exception for highly compressible nodata masks? A 
> common situation is that a slightly rotated sampling leaves thin 
> triangular perimeter nodata areas of which a compressed textual 
> description is under a kilobyte. E.g., have a flag saying if the mask is 
> in the xml file or outside.

Ray,

To be honest, later today I was thinking the same thing.  Bitmasks
are almost always very highly compressable, so Deflate compressing them
and 6bit ascii encoding them would likely produce data that could be
embedded into an XML file though it still might not scale so well for
multi-gigapixel images.

Best regards,
-- 
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