[Gdal-dev] Re: single ECW output from multiple input tiles

[Ken Boss]

>>>> fwarmerdam at gmail.com 5/16/2005 8:53:55 AM >>>
>In VRT there are "SimpleSources" and "ComplexSources".  The
>complex sources include support for nodata values that are not
>copied, and for on the fly scaling.   I *think* you would setup
>a complex source similarly to a simple source except that you
>use the element <ComplexSource> instead of <SimpleSource> and
>the complex source can have NODATA, ScaleOffset and ScaleRatio
>tags for which the values are used during image processing.
>
>If you can't get this to work let me know, and I will prepare an
example.
>
>I would warning that .vrt's have degrading performance as the number
>of sources goes up, so they aren't a great way of managing a mosaic
>of hundreds of images. 
>
>Best regards,
>-- 

Frank--

I changed my <SimpleSource>s to <ComplexSource>s, and added
<NoDataValue> tags, first as children of <VRTRasterBand> elements, and
then as children of the <ComplexSource> elements, but to no avail.  A
copy of my test.vrt file is attached.

As regards performance, I decided this weekend to ignore the offsite
problem and run a test with 600 three-band tiles totalling something
like 250 GB of input data.  It failed at 80% completion after 27 hours,
but only (I am reasonably certain) because I had neglected to increase
the size of my virtual memory paging file when I added a RAM upgrade to
the machine last week.  So I see some reason at least for cautious
optimism.

--Ken


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