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 <mauc...@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 <j...@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@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@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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