[gdal-dev] Nodata and compression artifacts

[Simon Shak]

I will look into the vet file. I often have multiple input files and didn't
see a way to use the cutline option with multiple input cutline.
On Nov 25, 2013 3:33 PM, "Even Rouault" <even.rouault at mines-paris.org>
wrote:

> Le lundi 25 novembre 2013 22:29:00, Simon Shak a écrit :
> > I’m working with gdalwarp to reprocess a large amount of imagery to be
> > compatible with another program that requires imagery to be in WGS84.
>  The
> > input imagery is compressed in MrSID format and does not include an
> > internal mask for nodata.  I don’t know if this is because the creator of
> > the imagery overlooked it, or if the format doesn’t support a mask.
>  Either
> > way, when I attempt to merge neighboring sets, I get odd bands of dark
> > color.  I’ve looked closely, and it is evident because at the edge of the
> > images are non 100% black pixels, that though I’m sending –srcnodata 0
> into
> > gdalwarp, they get read as pixels and progress through.  I’ve looked into
> > using the nearblack command on the files first, but the compression ratio
> > of the .SID files makes it such that the files don’t easily fit into my
> > hard drive array for pre-nearblacking them before processing, plus the
> > physical size of some of these files are large enough that the nearblack
> > takes a long time to run.  Without the nearblack step, my multithreaded
> > control script can process one chunk in a day, but adding the nearblack,
> > and it increases to a week at least.
> >
> >
> >
> > I’m looking for a solution that would not require making a large interim
> > uncompressed version and would hopefully not incur a lengthy additional
> > process.
> >
> >
> >
> > The simpler thoughts I have would be to adjust gdalwarp’s –srcnodata to
> > take a range option, much like nearblack, so that if it detects a pixel
> > (even in the middle) that is with the range specified would get ignored,
> or
> > a way to include an ancillary file that could contain a mask.  Either
> would
> > work for me, I have potential ways to quickly generate a mask for the
> input
> > files.  I’d think the mask could work much like .TIF can have a .TFW,
> that
> > a .MSK could be detected as well.
>
> You can use the -cutline option of gdalwarp if you have the mask as a
> shapefile
> or another OGR datasource.
> You could also use a VRT file to combine the MrSID imagery and add another
> band
> from TIF for example as the alpha/mask band.
>
>
> --
> Geospatial professional services
> http://even.rouault.free.fr/services.html
>
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