[gdal-dev] gdalwarp produces all black output

[peifer]

Even Rouault wrote
> Le jeudi 08 août 2013 19:44:04, Hermann Peifer a écrit :
>> On 2013-08-08 9:55, ludwig.hilger wrote:
>> > Hello everybody,
>> > 
>> > I am also a newbie and seem to have a similar problem, but cannot get
>> it
>> > solved. I am trying to reproject the following file:
>> > http://www.altmuehlnet.de/~hilger/Test_Smooth_0208_4258.tif
>> > I am using the following line:
>> > gdalwarp -et 0 -r bilinear -s_srs EPSG:4258 -t_srs EPSG:25832
>> > Test_Smooth_0208_4258.tif Test_Smooth_0208_4258_25832.tif
>> 
>> I downloaded your test file and noted that it has 10000x10000 pixel and
>> a real world extent of around 7x7 metres. So 1 pixel in your GeoTIFF
>> represents less than 1x1 mm. I can only blindly assume that some
>> rounding effects related to the small pixel size lead to the problem you
>> observed. I noted the same problem in my testing (I am using the MacPort
>> of GDAL 1.10, on my MacBook).
>> 
>> I re-defined the extent of your file to 1x1 degree and was able to warp
>> the resulting file without any problem:
>> 
>> $ gdal_translate Test_Smooth_0208_4258.tif out_1x1.tif -a_ullr 10 47 11
>> 46
>> 
>> $ gdalwarp out_1x1.tif out_25832.tif -t_srs epsg:25832 -et 0 -rb
>> 
>> Maybe someone from the GDAL devs has an explanation for this behaviour.
> 
> Herman,
> 
> you're right. The issue was due to the input pixel size being very small.
> I've 
> fixed that in ticket http://trac.osgeo.org/gdal/ticket/5190

I should have seen in the DEBUG output that before your fix, always the same
source pixel (Src=0,0,1x1 - which happened to have the value 0 in all bands)
was taken and warped into the various destination windows. Now it works as
expected.

Thanks, Hermann




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