Le mardi 20 novembre 2012 21:14:12, Etienne Tourigny a écrit : > Hi all, > > I just noticed that GDALBuildOverViews disregards all nodata pixels. > While this is useful in many cases, sometimes it can be desired to NOT > overlook nodata pixels. > > For example, I have a raster of sparse data (many nodata pixels), that > I am using gdaladdo to make down-sampled versions. The workflow is: > use gdaladdo with "mode" resampling and then gdal_translate to get > final downsampled image. > > A problem occurs on the edges of valid data, overview pixels get set > to a value which is clearly non-dominant in the higher-resolution data > - that is mostly nodata pixels. As the algorithm disregards the nodata > pixels, result is the most frequent valid data pixel. > > Would it be easy to fix this, or am I better off just making a copy of > the file without nodata, and then adding the nodata later?
Etienne, Mode resampling was contributed by Seth Price in http://trac.osgeo.org/gdal/ticket/2347 . Perhaps you could see with him. At first sight, I'd say that your arguments make sense, and that nodata should be treated as a regular value (like in nearest resampling). Ignoring nodata makes sense in bilinear or cubic resampling where you don't want to "average" with a dummy value. > > Thanks > Etienne > _______________________________________________ > gdal-dev mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/gdal-dev _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
