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

[John Twilley]

None of those resampling methods are well-suited to classified rasters
as far as I can tell.

The method that has worked best in the past was to take the majority
of a number of the nearest neighbors.  The 'mode' algorithm in
gdaladdo may do that, but I haven't checked the source code.

Jack.
--
mathuin at gmail dot com



2012/1/27 Dmitry Baryshnikov <polimax at mail.ru>:
> 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
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> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
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