[Gdal-dev] Performance of MrSID support in GDAL

[Frank Warmerdam]

On Tue, 01 Feb 2005 16:23:26 +0100, juergen.link at freenet.de
<juergen.link at freenet.de> wrote:
> Hi Folks,
> we are facing a strange problem using UMN Mapserver with MrSID support.
> When asking for raster data from a compressed source the mapserver on our fast Linux box
> takes about 4.5 seconds to decode MrSID data. A much smaller and slower Windows box
> does the job in less than a second.
> We cooked down the problem and found 2 possible hints:
> - LizardTech's  tool mrsiddecode takes about 0.5 sec to render a JPEG file
>       mrsiddecode -i 0259005590_dop5__c_025.sid -o test.jpg -ulxy 500 500 -wh 800 600
> - while gdal's tool  takes 4.5 sec
>       gdal_translate 0259005590_dop5__c_025.sid test_gdal.jpg -srcwin  500 500 800 600 -of JPEG
> So it seems to be a lack of gdal lib, rather  than mapserver's?
> Did we do any wrong with our compile job??

Jurgen,

I believe the problem is that GDAL is requesting data on a block (full
image width) basis.  I went to download the latest MrSID SDK but
got scared off again by all the licensing language.  It is very hard for
me to understand it all and be confident I would be adhering to it
properly.  

However, I guess I will need to get over this hump so I can do some
work on the driver. 

Your use-case is definately the one we want to operate efficiently.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent