[gdal-dev] gdalwarp makes landcover files blocky when shrinking pixel size

[Dmitry Baryshnikov]

27.01.2012 20:19, John Twilley пишет:
> After retrieving the files and building VRTs from them, I run the
> following gdalwarp commands:
>
> gdalwarp -q -multi -t_srs "+proj=aea +datum=NAD83 +lat_1=29.5
> +lat_2=45.5 +lat_0=23 +lon_0=-96 +x_0=0 +y_0=0 +units=m" -tr 6 6 -te
> 2002944 2271744 2016768 2288640 \
>   -srcnodata -340282346638528859811704183484516925440 -dstnodata 0
> ND302HT.vrt ND302HT.tif
> gdalwarp -q -multi -t_srs "+proj=aea +datum=NAD83 +lat_1=29.5
> +lat_2=45.5 +lat_0=23 +lon_0=-96 +x_0=0 +y_0=0 +units=m" -tr 6 6 -te
> 2002944 2271744 2016768 2288640 \
>   -srcnodata 255 -dstnodata 11 L0102HT.vrt L0102HT.tif
>
> The only differences between the lines are the nodata values.
>
> Jack.
> --
> mathuin at gmail dot com
>
>
>
> On Thu, Jan 26, 2012 at 22:49, Dmitry Baryshnikov<polimax at mail.ru>  wrote:
>> 27.01.2012 3:39, John Twilley пишет:
>>> I am working with elevation and landcover data downloaded from the
>>> USGS.  I use gdalwarp to convert the data to a much smaller pixel. The
>>> elevation data works very nicely with cubic resampling, but the only
>>> resampling that works at all for the landcover data is
>>> nearest-neighbor and that's very blocky.  When I last worked with
>>> landcover data, I used a majority algorithm which produced smoother
>>> output -- but that algorithm is not implemented in gdalwarp.
>>> I am looking over the source to gdalwarp to see how hard it is to add
>>> a new algorithm.  Other than that, though, what options are available
>>> to me?  Thanks in advance!
>>> Jack.--
>>> mathuin at gmail dot com
>>> _______________________________________________
>>> gdal-dev mailing list
>>> gdal-dev at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>>
>>>
>> Hi John,
>>
>> That is your command line string for gdalwarp?
>>
>> Best regards,
>> Dmitry
>>
>> _______________________________________________
>> gdal-dev mailing list
>> gdal-dev at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
Hi John,

Try to add "-r cubic" command parameter
For example:

gdalwarp -q -multi -t_srs "+proj=aea +datum=NAD83 +lat_1=29.5
+lat_2=45.5 +lat_0=23 +lon_0=-96 +x_0=0 +y_0=0 +units=m" -tr 6 6 -r cubic -te
2002944 2271744 2016768 2288640 \
  -srcnodata -340282346638528859811704183484516925440 -dstnodata 0
ND302HT.vrt ND302HT.tif

You can found additional parameters description here: http://www.gdal.org/gdalwarp.html
I have tested -r parameter and it works.

Best regards,
Dmitry