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

[Ken Boss]

>>>> Gabriel Ebner <ge at gabrielebner.at> 5/14/2005 7:13:23 AM >>>
>
>Ken Boss wrote:
>
>> I'm wondering if any of the tools commonly found in this
neighborhood
>> might be capable of constructing a single mosaicked ECW output
directly
>> from a collection of tiled inputs, without going through an
intermediate
>> (uncompressed, full-res) file.  I'm pretty sure gdal_merge.py won't
be
>> able to fit the bill on this one, are there other options?
>
>How about using a vrt dataset?  That should actually be able handle
huge
>mosaics.  I'm currently using a rewritten gdal_merge.py (attached) to
>generate such files and it works pretty well.  It should be possible
to
>gdal_translate that to ecw without problems.
>
>        Gabriel.

Gabriel--

Many thanks, this is very nearly exactly what I was looking for.  vrt
datasets feed nicely into gdal_translate for outputting to ecw.  My only
remaining obstacle is ensuring that valid image data doesn't get
overwritten by nodata values from overlapping inputs.

Reading at
http://xserve.flids.com/pipermail/gdal-dev/2004-September/007053.html,
I got the idea that I could add a <NoDataValue>0</NoDataValue> tag to
the VRTRasterBand sections of the .vrt file in order to address this
issue, but alas, this seems to have no effect, at least when translating
to ecw.  I was hoping that maybe a source nodata value could be passed
as an ECW creation option, but no such luck.

Any suggestions welcome...

--Ken