[gdal-dev] Bad gdalwarp interpolation

[Calogero Mauceri]

I just submitted a bugreport for this issue
https://github.com/OSGeo/gdal/issues/10512

On Fri, Jul 26, 2024 at 12:42 PM Calogero Mauceri <mauceri at actgate.com>
wrote:

> Thanks Javier for your reply.
>
> I'd like to avoid changing the source file work around.
> We are using gdalwarp C++ API as part of a general application that can
> open any kind of file.
>
>
>
> On Fri, Jul 26, 2024 at 12:26 PM Javier Jimenez Shaw <j1 at jimenezshaw.com>
> wrote:
>
>> Hi
>>
>> I do not know if there is anything wrong in GDAL. It looks like
>>
>> As a workaround, you can first convert the projection to be centred at
>> lon=0 with something like this (I kept the same radius as the original to
>> minimize distortion). You can add bilinear interpolation or not, as you
>> wish.
>> gdalwarp -t_srs '+proj=eqc +a=2439400 +b=2439400 +lon_0=0.000000
>> +lat_0=0.000000 +x_0=0 +y_0=0 +units=m +no_defs'-overwrite
>> msgr_dem_low_res.tif centred.tif
>> And then cut with your command.
>>
>> I know it is not optimal because it is converting the full image. But the
>> output is not blur.
>>
>> Cheers,
>> Javier.
>>
>>
>>
>> On Fri, 26 Jul 2024 at 09:49, Calogero Mauceri via gdal-dev <
>> gdal-dev at lists.osgeo.org> wrote:
>>
>>> Hi,
>>>
>>> I'm rendering a 256x256 tile from a mercury dem. I noticed the gdalwarp
>>> is producing a bad output when using interpolation with the following
>>> command
>>>
>>> gdalwarp -of PNG -r bilinear -t_srs '+proj=eqc +a=2439700 +b=2439700
>>> +lon_0=0.000000 +lat_0=0.000000 +x_0=0 +y_0=0 +units=m +no_defs' -ts 256
>>> 256 -te -958067.949620 -958067.950079 0.000460 0.000000 -overwrite
>>> msgr_dem_low_res.tif tile.png
>>>
>>> The output image is kind of blurred/low resolution
>>> [image: tile.png]
>>>
>>> On the other side, it looks good if nearest interpolation is used
>>>
>>> gdalwarp -of PNG -t_srs '+proj=eqc +a=2439700 +b=2439700 +lon_0=0.000000
>>> +lat_0=0.000000 +x_0=0 +y_0=0 +units=m +no_defs' -ts 256 256 -te
>>> -958067.949620 -958067.950079 0.000460 0.000000 -overwrite
>>> msgr_dem_low_res.tif tile.png
>>>
>>> [image: tile.png]
>>>
>>>
>>> The problem seems related to the fact that the right edge of the tile is
>>> around longitude 0, while the source image is a full globe/360 degrees
>>> image centered at 180 longitude
>>>
>>> If I reduce the tile size to 255x255 for avoiding the 0 longitude at the
>>> edge, then the interpolated output file looks much better
>>>
>>> gdalwarp -of PNG -r bilinear -t_srs '+proj=eqc +a=2439700 +b=2439700
>>> +lon_0=0.000000 +lat_0=0.000000 +x_0=0 +y_0=0 +units=m +no_defs' -ts 255
>>> 255 -te -958067.949620 -950583.044220 -7484.905400 0.000000 -overwrite
>>> msgr_dem_low_res.tif tile_255.png
>>>
>>> [image: tile_255.png]
>>>
>>> Am I doing something wrong or is this a bug in GDAL?
>>>
>>> I'm using the mercury dem from here
>>> https://pdsimage2.wr.usgs.gov/Messenger/MESSDEM_1001/DEM/GLOBAL/IMG/
>>> Here is a lower resolution of the same dem for testing purpose
>>> https://
>>> <https://pdsimage2.wr.usgs.gov/Messenger/MESSDEM_1001/DEM/GLOBAL/IMG/>
>>> files.actgate.com/terrain/mercury/msgr_dem_low_res.tif
>>>
>>> Thanks in advance for your help,
>>> Calogero Mauceri
>>>
>>> --
>>> Calogero Mauceri
>>> Software Engineer
>>>
>>> Applied Coherent Technology Corporation (ACT)
>>> www.actgate.com
>>> _______________________________________________
>>> gdal-dev mailing list
>>> gdal-dev at lists.osgeo.org
>>> https://lists.osgeo.org/mailman/listinfo/gdal-dev
>>>
>>
>
> --
> Calogero Mauceri
> Software Engineer
>
> Applied Coherent Technology Corporation (ACT)
> www.actgate.com
>


-- 
Calogero Mauceri
Software Engineer

Applied Coherent Technology Corporation (ACT)
www.actgate.com
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