[gdal-dev] Question on block size in the kakadu driver

[Kurt Schwehr]

Frank, Even or anyone with experience with jp2k block sizes,

Any chance you could comment on the change I proposed here?

https://trac.osgeo.org/gdal/ticket/6764

Is it reasonable to change this:

    if( nRasterXSize >= 2048 )
        nBlockXSize = 2048;
    else
        nBlockXSize = nRasterXSize;

    if( nRasterYSize >= 256 )  // <- 256
        nBlockYSize = 128;       // <- 128 ???
    else
        nBlockYSize = nRasterYSize;

Into:

         nBlockXSize = std::min(nRasterXSize, 2048);
         nBlockYSize = std::min(nRasterYSize, 128)

or

         nBlockXSize = std::min(nRasterXSize, 2048);
         nBlockYSize = std::min(nRasterYSize, 256)

Neither of those is the same behavior and the the jump from 256 back to 128
is not explained in the revision log.  Which behavior will have better
performance for a average case or will it matter?   The difference will be
between 262K cells or 524K cells.  With doubles, that will be 2 or 4 MB for
a single block from one band.  I'm thinking 128 is likely going to work
better with RAM caches.
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