[FWTools] ECW Conversion and TIF Tiling

Eric Legge Smith e.smith13 at pgrad.unimelb.edu.au
Wed Dec 20 20:13:53 EST 2006

Hello List

Thank you to everyone who supplied helpful tips on how to convert ECW
files and tile TIF's.

Re. ECW conversion
I'm running Mapserver on debian linux and the version of GDAL from debian
package manager (, released 2005/03/13) doesn't support the ECW
file type.

Re. TIF ->GeoTIFF->Tiles
I used gdal_translate to convert the TIFF +TFW to a GeoTIFF (20000 x 20000
pixels, 1.2Gb) and wrote a shell script to 'slice and dice' this GeoTIFF
into 400 1000x1000 pixel TIFF tiles. gdaltindex then created the tile
index which worked with Mapserver, however there was no noticable increase
in display speed and when viewing at very large scales, the web server
would time out.
In an alternative approach, I used gdaladdo to add external overviews to
the GeoTiff and reverted to using the GeoTIFF + external overviews rather
than the tiles + tile index as the data source for Mapserver. This proved
to be very effective, and I can now display the raster at any scale
without the server timing out.
Question - Should I stick with the single GeoTIFF + external overviews as
the Mapserver data source, or is there some way to better utilise the
tiled TIFFs

Thank you

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