Le vendredi 14 août 2015 17:17:34, Ivan Castellucci Vidal a écrit : > Hi, list > > First of all, I searched on the list but I hadn't found anyone with the > same issue as me. > > I'm working with aerial images of fields that I use as input to my program > which needs to process the images and find some visual patterns and then > give some output for the users. > > I use georeferenced images because I need to extract geographic data after > my program process the image. So, when I warp my image with gdalwarp it > rotates the image and as a consequence of northing up the image, it rotates > the raster and adds 4 black triangles to make it rectangular. > > The problem is, when I run my program, this "borders" are messing with my > algorithm and are a source of inaccuracy on the image processing. I can get > rid of them with more image processing but any extra step is > computationally heavy, specially when using large images.
During the warping, you could add an alpha channel or set a destination nodata value so as to be able to identify the generated transparent areas > > I would need to avoid the rotation of the raster after gdalwarp is used to > implant the geotransformation on the destination image. I don't really care > if the image is not north up after warping it so I may not need gdalwarp > and instead I may be able to use some other solution based on the C API if > needed. > > If it's relevant, the source images are in JPEG format and the destination > are in GeoTiff format, the transformation is done by using 3 (sometimes > more) GCPs and I'm using EPSG:4326 projection. Instead of warping the image, you could compute a geotransformation matrix that would include rotational terms with GDALGCPsToGeoTransform() http://www.gdal.org/gdal_8h.html#ae44b32f08d61072dddbdd30ac8ca962b and set it to your geotiff with GDALSetGCPs() http://www.gdal.org/gdal_8h.html#acd47aa85ca5751fbe9ea09c1a2341ef8 > > I didn't explained details of the pattern recognition process because I > think it's irrelevant to my problem and it will be confusing but if you > need any, just let me know. > > > Any help is appreciated, > > Thanks in advance -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev