[Gdal-dev] ECW mosaicking

[Frank Warmerdam]

Jose Luis Gomez Dans wrote:
> Hi! I have downloaded the ECW SDK from ERMapper, and have recompiled GDAL
> against it. It works fine. However, I have a couple of questions: 1.- Can I
> use gdal_merge to *ehm* merge a large number of large GeoTIFF files into a
> single ECW file? I have tried and I get the following error: "Format driver
> ecw does not support creation and piecewise writing. Please select a format
> that does, such as GTiff (the default) or HFA (Erdas Imagine)." If not, what
> is the best way to merge these files using GDAL and the ECW SDK?

Jose,

Generally gdal_merge.py and gdalwarp won't support mosaicing into a CreateCopy
format such as compressed formats like ECW.  You generally need to mosaic into
an uncompressed format, like Erdas Imagine (driver is HFA), and then compress
the final mosaic into the compressed file.

> 2.- What about the file size limit? There used to be a 500Mb limit, but
> according to <http://www.ermapper.com/ProductView.aspx?t=212>, I can see no
> limitation anywhere (or in the gdal website). Is this still current. Given
> my inability to merge files into an ECW, I cannot test it myself yet :)
> 
> Many thanks! Jose

I am not aware of a change with regard to the 500MB limit.  In the past it
did not apply if the GPL-compatible license was being used, but there are
various conditions you need to meet for this to be true.  If you meet those
conditions you can use the "-co LARGE_OK=YES" creation option when creating
your ECW to indicate that you are appropriately licensed to create large
ecw files.

If the limit *has* been removed from the software you should not need to do
this.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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