[gdal-dev] Q: on gdalwarp of ecw file

[Even Rouault]

Le lundi 17 décembre 2012 20:50:27, Stephen Woodbridge a écrit :
> Hi all,
> 
> I have an ECW file, see gdal info below.  I need to reproject this into
> EPSG:900913 or EPSG:3857
> 
> Do I need a key to make the output file ECW?

If you use SDK 4.x, yes. With SDK 3.X if the image was < 500 MB, you didn't 
need a licence.

> 
> The performance vs size when zooming out is impressive with ECW, but it
> does not look like I have ability to create ECW. Are there better
> formats then GTif in the list below?

JPEG2000 or MrSID are somewhat similar to ECW.

> 
> 
> $ gdalwarp -t_srs EPSG:900913 -of GTiff -co TILED=YES -co COMPRESS=JPEG
> Saraji_South.ecw Saraji_South-900913.tif
> Creating output file that is 34551P x 32332L.
> Processing input file Saraji_South.ecw.
> 0...10...

I'd recommand also adding -co PHOTOMETRIC=YCBCR that will make the resulting 
file typically 2 to 3 times smaller (at the expense of some quality loss of 
course)

See "About JPEG compression of RGB images" section of 
http://gdal.org/frmt_gtiff.html

> 
> This seems to be working, I suspect this will bulk up after I add
> overviews.

Yes, with overviews you should have good performance.