Le mardi 10 décembre 2013 16:48:31, Ivan Lucena a écrit : > Hi Even, > > > From: [email protected] > > To: [email protected] > > Subject: Re: [gdal-dev] Default GeoTransform for MEM driver > > Date: Mon, 9 Dec 2013 20:54:35 +0100 > > CC: [email protected]; [email protected]; [email protected] > > > > Le lundi 09 décembre 2013 18:08:19, Ivan Lucena a écrit : > > > The other problem with that documentation is the return code. CE_Failue > > > means that the driver does not support it and/or that the dataset > > > doesn't have it. > > > > The current behaviour of the MEM driver doesn't particularly shock me. It > > seems OK to return CE_Failure if SetGeoTransform() hasn't been > > explicitely called to define it. And as far as the default geotransform, > > it is a matter of taste. [ 0, 1, 0, 0, 0, 1] would be indeed a bit more > > classical for a ungeoreferenced image, but one can consider that if > > GetGeoTransform() returns CE_Failure, the returned geotransform is to be > > ignored. > > That is good to know. So it really doesn't matter if the driver support > geotransformation or not. > > But my concern is when it returns CE_None. What does it really means > because I was checking some driver's implementation of GetGeoTransform and > I noticed that some of then always return CE_None no matter what. > So would > that be possible that a dataset is *ungeoreferenced* and a driver returns > CE_None with the default values [0, 1, 0, 0, 0, 1]. > Should we trust that > those values [0, 1, 0, 0, 0, 1] are correct or are they just a default > filler? > > For example, to get [0, 1, 0, 0, 0, 1] we should expect a world-file that > should be something like: > > 1.0000000000 > 0.0000000000 > 0.0000000000 > 1.0000000000 > 0.5000000000 > 0.5000000000 > > Not: > > 1.0000000000 > 0.0000000000 > 0.0000000000 > 1.0000000000 > 0.0000000000 > 0.0000000000 > > Anyway, I will trust that the CE_None means that the geotransformation > values are correct but should I will also check if the values are equal to > [0, 1, 0, 0, 0, 1] just in case? And what to do if they are?
I'm not sure to know the ultimate answer to your questions. My understanding of http://www.gdal.org/classGDALDataset.html#af9593cc241e7d140f5f3c4798a43a668 is that when there's no projection space associated to a raster, it should return (0,1,0,0,0,1) and CE_Failure. But they are certainly drivers that return (0,1,0,0,0,1) and CE_None. They should likely be fixed to return CE_Failure instead. But you can also test if the geotransform is (0,1,0,0,0,1) since it isn't a likely real geotransform. Even -- Geospatial professional services http://even.rouault.free.fr/services.html _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
