Thanks Even, didn't know about gdalmove. I'll try !!
Il giorno gio 18 nov 2021 alle ore 15:47 Even Rouault < even.roua...@spatialys.com> ha scritto: > Black borders are completely expected: reprojection changes the geometry > of the image. > > That said, if the area of interest is sufficiently small and the geometry > change being approximatively an affine transformation, you can try > https://gdal.org/programs/gdalmove.html instead of gdalwarp to only alter > the georeferencing information and not touch pixel values at all. > > Even > Le 18/11/2021 à 15:34, Lorenzo Di Giacomo a écrit : > > Hi Carl, thanks for your reply, i noticed that it happens even if i just > reproject the image, without cutting. > Of course the dstalpha works, but it increases the size of the image and > it changes its nature (adding another band) since this operation is an > intermediate operation the resulting image can't be different from the > original, just reporojected. > > > > Il giorno gio 18 nov 2021 alle ore 14:11 Carl Godkin <cgod...@gmail.com> > ha scritto: > >> Hi Lorenzo, >> >> I have faced this and there are two things to consider. >> >> First, you can specify the georeferenced extents _and_ the SRS of the >> extents using something like this: >> >> gdalwarp -t_srs EPSG:3857 \ >> -te_srs EPSG:4326 -te -109 32 -102 36 \ >> input.tif output.tif >> >> Note that I'm warping to one coordinate system but trimming based on >> another one. Is it possible that your black boundary is due to trimming in >> the wrong coordinate system? For instance, if your input map is projected >> but the boundary of the map consists of parallels of latitude or >> meridians of longitude, then you could use something like the above. (You >> can actually get even fancier by trimming with polygons too; see this >> example for inspiration: >> https://gis.stackexchange.com/questions/45053/gdalwarp-cutline-along-with-shapefile >> .) >> >> Second, recognize that the output will always be a rectangle in the >> output SRS. If the black border is due to "no data" areas outside the >> input map's extent appearing in the output map, then you can use -dstalpha >> ("Create an output alpha band to identify nodata (unset/transparent) >> pixels.") to mark the output pixels that shouldn't be part of the map. >> Basically your black pixels become transparent in this case. >> >> I hope that helps, >> carl >> >> >> On Wed, Nov 17, 2021 at 8:11 AM Lorenzo Di Giacomo <loridi...@gmail.com> >> wrote: >> >>> Hi all, i have a question, how is it possible to avoid black borders >>> after reprojection with "gdal_warp" ? >>> Basically i have an image that is little rotated, when i reprojected >>> from 32632 to 4326 the resulting image has black borders more or less tight >>> depending on the rotation. >>> I saw i can change the colors of those no_data (using -dstnodata) but >>> how can i do if i dont want it at all? Adding another band result in a size >>> increase, that i don't want either. >>> >>> Thanks !! >>> _______________________________________________ >>> gdal-dev mailing list >>> gdal-dev@lists.osgeo.org >>> https://lists.osgeo.org/mailman/listinfo/gdal-dev >>> >> _______________________________________________ >> gdal-dev mailing list >> gdal-dev@lists.osgeo.org >> https://lists.osgeo.org/mailman/listinfo/gdal-dev >> > > _______________________________________________ > gdal-dev mailing > listgdal-dev@lists.osgeo.orghttps://lists.osgeo.org/mailman/listinfo/gdal-dev > > -- http://www.spatialys.com > My software is free, but my time generally not. > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/gdal-dev >
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