[gdal-dev] Cropping a raster by a polygon - only nodata outside polygon wanted

[mathieu]

The problem is that I don't know want an alpha channel because some of my
users work on MapInfo and MapInfo doesn't deal with alpha channels..

2015-01-14 11:39 GMT+01:00 Even Rouault-2 [via OSGeo.org] <
ml-node+s1560n5181432h49 at n6.nabble.com>:

> Mathieu,
>
> If 0 is a valid value at some locations of your raster, then you cannot
> use it
> as the nodata value. Use an alpha band instead for example by using
> -dstalpha
> instead of -dstnodata 0
>
> Even
>
> > Hello,
> >
> > I crop a 3 band raster by a polygon with the following formula :
> > /gdalwarp -of GTiff -cutline polygon.shp -cl polygon input.tif
> output.tif
> > /
> > But pixels outside my polygon are assigned the 0 value. I'd like them to
> > have nodata
> >
> > If I put the -dstnodata 0 option :
> > /gdalwarp -of GTiff -cutline polygon.shp -cl polygon input.tif
> output.tif
> > -dstnodata 0/, all the pixels in each of the 3 bands that contain the 0
> > value will be turned to nodata, even if they are contained in my
> polygon.
> >
> > Hence, 127 0 222 will become 127 nodata 222
> > or 0 127 222 will become nodata 127 222
> >
> > How to put the nodata value only outside my polygon ?
> >
> > Thanks a lot in advance !
> >
> > Mathieu
> >
> >
> >
> > --
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