VS: [UMN_MAPSERVER-USERS] PHP Mapscript - Jpeg2000

[Frank Warmerdam]

On 12/15/05, Rahkonen Jukka <Jukka.Rahkonen at mmmtike.fi> wrote:
> But there is one thing I am not happy with: creating overviews with gdaladdo is painfully slow. It took 20 hours with 3 GHz Pentium to build those  32 64 128 256 overviews for my virtual raster layer. I think that is awfully long time. But fortunately I am almost sure that this speed could be dramatically improved. I made another test with Kakadu executables, and taking out a 1:32 downsampled version of one image file took no more than 2 seconds. For those who know Kakadu, my command was "kdu_expand -reduce 5 -i test.jp2 -o reduce.ppm".  Based on that I estimated that creating an usable overview file for my set should not take very much longer than [113 (images) x 2 (seconds per image) x 4 (downsampling levels)] = 900 seconds = 15 minutes. It would be quite an improvement, compared to 20 hours! Who will be the one to implement it? I cannot, I am no programmer.

Jukka,

JPEG2000 reading is quite sensitive to the particulars of
how the reading is done.   Particular image access patterns
can be dramatically slower than others.  I suspect that is
part of the issue with the slow overview building.

The other thing to keep in mind is that the .vrt mechanism
was not intended to scale up to hundreds of input images.
Under some circumstances it may exhibit quite poor performance.

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