[gdal-dev] Speed up MrSid warping

[Jason Beverage]

Hi Frank,

Thanks for the tips, I'll tinker around and try to run some tests with
GDAL_ONE_BIG_READ and try to get things working so that the MrSid
isn't wrapped in a VRT and see if that helps.

Thanks!

Jason

On Sat, Aug 7, 2010 at 9:25 AM, Frank Warmerdam <warmerdam at pobox.com> wrote:
> On Fri, Aug 6, 2010 at 11:34 AM, Jason Beverage <jasonbeverage at gmail.com> wrote:
>> Hi all,
>>
>> I have quite a few MrSid files that are in UTM that I want to mosaic
>> together into some epsg:4326 tiles.  I've written some python scripts
>> to produce the appropriate gdal_warp commands to create the tiles, but
>> they are running extremely slow.
>>
>> I've read various mailing list posts and blogs about different options
>> for MrSid like this one:
>> http://priour.wordpress.com/2007/01/09/massive-performance-improvements-in-converting-mrsid-files/
>> which highlights using GDAL_FORCE_CACHING = YES to speed up a
>> gdal_translate when using MrSids.  I've also read about using
>> GDAL_ONE_BIG_READREAD to speed things up in MapServer.  Which option,
>> or any other options, would be helpful for gdal_warp?
>
> Jason,
>
> Generally speaking gdalwarp tries to read in big chunks, and it would be
> beneficial to enable GDAL_ONE_BIG_READ to on and avoid caching.
> Caching is more beneficial when doing lots of little reads.
>
>> Also, my MrSids are wrapped in VRTs to provide coordinate system info.
>>  If I use the VRTs will the GDAL_FORCE_CACHING and GDAL_ONE_BIGREAD
>> options be used?
>
> When access is done through a VRT it forces access
> at a smaller chunk size which can be at least somewhat
> painful for formats like mrsid for which each read is quite
> expensive.  You might want to consider ways of associating
> the coordinate system without using the VRT.  Note that
> gdalwarp does have a -s_srs switch to set the source
> coordinate system if it is missing or wrong on the source
> file.
>
> Best regards,
> --
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial Programmer for Rent
>