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 >
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