[Gdal-dev] Nodata bitmasks / null processing

[Frank Warmerdam]

Simon Perkins wrote:
> So, would the default implementation return a universal RasterBand 
> derived class that implements IReadBlock() and IWriteBlock() in terms of 
> the underlying format RasterIO() method in conjunction with NODATA values?

Simon,

I think this is quite plausible, with the default implementation of
GetBitmask() returning NULL if there is no nodata value set.

> One thing though - if the GetBitmask() method is a RasterBand method, 
> then presumably invoking that method on a RasterBand returned by 
> GetBitmask() wouldn't make sense. Either this could just raise some kind 
> of error. Or we could make GetBitmask() a method of the Dataset instead.

It is up to the drivers creating custom classes for their GetBitmask()
result to ensure those don't in turn return bitmasks, and don't have
a nodata value set on them.

I think GetBitmask() being a method on GDALRasterBand, instead of
the dataset is important as it clearly establishes the association.

I am wondering, a bit how we would represent the case where there is
one nodata bitmask for a whole dataset.  That it, one mask applying
to all bands.  Perhaps all bands just return the same object?

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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