[Mapserver-users] Mr SID & Mapserver

[Frank Warmerdam]

Jim Burnett wrote:
> well we converted a 120meg Mr Sid file using the Mr Sid viewer and it 
> was like 6 gigs in Tiff format. Linux doesnt support any files over 2 
> gigs. :-(

Jim,

It is not completely true that Linux does not support files larger than
2GB.  The 32bit file access API supports only files up to 2GB but the
64bit API supports large files.  The 64bit file API is standard on
Linx 2.4.x kernels and later as far as I know, and can be patched into
2.2.x kernels.

Some applications do support the 64bit file API and some do not.   The
GDAL library and libtiff can be built to use the 64bit and so to support
large files.

All that said, due to the internal use of 32bit offsets in the TIFF format,
a TIFF file cannot effectively be much larger than 4GB anyways.

For some imagery data types a JPEG compressed tiled TIFF file with overviews
should give good compression and excellent access performance for large
images.  The compression will (presumably) not be as good as MrSId, but
I would imagine that a file that was 120meg in MrSID could be represented
in a JPEG compressed TIFF file not much larger than double the size of the
original.

Nevertheless, proper support for MrSID, ECW, and especially JPEG2000 seems
to be the best objective.

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