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

[Kurt Schwehr]

Even,

Thanks!  I'm working on a change that will do:

nBlockXSize = std::min(nRasterXSize, 2048);

nBlockYSize = std::min(nRasterYSize, 128);


Getting a performance monitoring system setup is definitely on my todo
list, but sadly still down a ways.


On Thu, Jan 5, 2017 at 7:40 AM, Even Rouault <even.rouault at spatialys.com>
wrote:

> On jeudi 5 janvier 2017 07:18:45 CET Kurt Schwehr wrote:
>
> > 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 code is a bit weird indeed. But the block size of smallish datasets
> has no real importance, so if you find it more reasable, switching the
> condition to if ( nRasterYSize >= 128 ) (or the equivalent std::min())
> should have no adverse consequences.
>
>
>
> Block size in the case of JPEG 2000 is really hard to come with. A smarter
> block size logic would depend on JPEG 2000 tiling, presence of precincts,
> etc... This also could depend on the read pattern. Would deserve extensive
> testing to come out with the ideal formula... In the case of JP2KAK,
> there's also a IRasterIO() implementation that causes the block size to not
> be used at all in typical read scenarios.
>
>
>
>
>
> > 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.
>
>
>
> FWIIW, JPEG2000 doesn't support double (at least not in the base standard)
>
>
>
>
>
> --
>
> Spatialys - Geospatial professional services
>
> http://www.spatialys.com
>



-- 
--
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