[gdal-dev] Problem with nodata values

[Frank Warmerdam]

Rainer M Krug wrote:
> Hi
> 
> I have a geotiff and want to use gdalwarp to warp to it into a
> different projection.
> I do the following:
> 
> gdalwarp -s_srs EPSG:32734 -t_srs '+proj=longlat +ellps=WGS84
> +no_defs' Outeniqua.tiff Outeniqua_wgs84.tiff
> 
> The problem is, that in Outeniqua_wgs84.tiff, the nodata values from
> Outeniqua.tiff become translated into -9999. In addition, the areas
> new to Outeniqua_wgs84.tiff (due to the warping) become 1.
> 
> Which options do I have to use to keep the nodata values and to make
> the values of the "new areas" also as nodata values?

Rainer,

I believe you want to pass the warp option INIT_DEST=-9999 to set all pixels
that do not come from the source file to -9999.

This is done with the -wo flag to gdalwarp.

eg.

gdalwarp -wo INIT_DEST=-9999 ...

The avalilable warp options are described in a web page available linked off
the gdalwarp utility page.

Best regards,
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