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

[Even Rouault]

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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