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

[Dmitry Baryshnikov]

27.01.2012 23:30, John Twilley пишет:
> Cubic is fine for the elevation, but it doesn't work on the landcover.
> which is the problem I originally mentioned.
>
> Jack.
> --
> mathuin at gmail dot com
>
>
>
> 2012/1/27 Dmitry Baryshnikov<polimax at mail.ru>:
>> 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
>>
>>
>> _______________________________________________
>> gdal-dev mailing list
>> gdal-dev at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>
Hi John,
You can use resampling methods:
near: nearest neighbour resampling (default, fastest algorithm, worst 
interpolation quality).
bilinear: bilinear resampling.
cubic: cubic resampling.
cubicspline: cubic spline resampling.
lanczos: Lanczos windowed sinc resampling.

And what method do you need?

Best regards,
     Dmitry