[gdal-dev] gdalwarp's default nodata value

Chaitanya kumar CH chaitanya.ch at gmail.com
Wed May 12 00:55:33 EDT 2010


On Wed, May 12, 2010 at 5:07 AM, Joaquim Luis <jluis at ualg.pt> wrote:

> Hi,
> Before filling a ticket I would like to ask here if this gdalwarp behavior
> is the intended one.
> When I convert a grid from geogs to UTM the nodatavalues are filled with
> zeros.
> I get the expected behaviour if I use the -dstnodata with a numeric value,
> but I found no way tom tell it use NaN.
> Summary
> This puts zeros on the nodata zone, but I don't find it correct as "0" is
> not exactly a natural nodata value. For my habits NaN is the natural no data
> value.
NaN should always be treated as a special case in coding. Imagine performing
a type conversion.
Since we usually deal with real world data, we know the data value range. We
should be able to choose a nodata value not in the data range.

> gdalwarp -s_srs "+proj=latlong" -t_srs "+proj=utm +zone=29 +datum=WGS84"
> swath_grid.grd lixo_utm.tiff
> Furthermore when I load the " lixo_utm.tiff" in Mirone is does not
> recognize a nodata value, whilst if I do this instead
> gdalwarp -s_srs "+proj=latlong" -t_srs "+proj=utm +zone=29 +datum=WGS84"
> -dstnodata 1 swath_grid.grd lixo_utm.tiff
> than "1" is recognized as the nodata. I have not investigated the metadata
> to see why the "0" is not set to represent the nodata.
Perhaps swath_grid.grd doesn't have a nodata value set.

> Thanks
> Joaquim Luis
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> gdal-dev at lists.osgeo.org
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Best regards,
Chaitanya kumar CH.
/tʃaɪθənjə/ /kʊmɑr/
17.2416N 80.1426E
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