Hi Even thanks for the info - I created a ticket (#4904) so it's not forgotten and added sprice in CC - although he hasn't seemingly been active in gdal for a few years.
Etienne On Tue, Nov 20, 2012 at 8:36 PM, Even Rouault <[email protected]> wrote: > 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
