Finally I've reached the point: GDAL's driver is opening the ASCII as Float64, consequently QGIS treats it this way. I wonder why gdalinfo and gdal_translate treat it as Float32 instead....
giovanni 2014-07-05 18:53 GMT+02:00 G. Allegri <[email protected]>: > The problem was simpler then it appeared: I didn't realize that QGIS > output is Float64. > Yet I don't know why QGIS chosed to use this data type... > > giovanni > > > 2014-07-05 17:56 GMT+02:00 Even Rouault <[email protected]>: > > Le samedi 05 juillet 2014 17:25:48, G. Allegri a écrit : >> > > QGIS is usually just calls to gdal, which makes this even more >> > > mysterious. >> > >> > Yes, in the end it uses gdal, but it chooses the way blocks are read and >> > written. >> > If I remember correctly geotiff final sizes may depend on block ordering >> > and memory alignment. >> >> In that instance, the target geotiff has a natural block dimension which >> is a >> raster line. >> If QGIS writes the geotiff by 256x256 blocks (this is just a guess. I've >> not >> verified), the same raster line will be written several times. As it is a >> compressed geotiff, the resulting raster line will be each time being >> bigger >> since the initial zeros will be replaced by actual values. And if the new >> size >> of the line is bigger than its previous size, the new line will be >> rewritten >> at the end of the file, losing the space previously occupied. >> >> > Maybe this is the case, QGIS raster provider not doing the best at this >> > level? Don't know, but this discussion is for the QGIS ml ;) >> > >> > giovanni >> > >> > > On 7/5/2014 9:09 AM, G. Allegri wrote: >> > > > I agree with you David, I'm surprised too. >> > > > Anyway, gdal_translate is run without compression options. >> > > > I've written to the QGIS devs (it was the software) to verify what's >> > > > happening with its raster file writer code... >> >> -- >> Geospatial professional services >> http://even.rouault.free.fr/services.html >> > > > > -- > Giovanni Allegri > http://about.me/giovanniallegri > Twitter: https://twitter.com/_giohappy_ > blog: http://blog.spaziogis.it > GEO+ geomatica in Italia http://bit.ly/GEOplus > -- Giovanni Allegri http://about.me/giovanniallegri Twitter: https://twitter.com/_giohappy_ blog: http://blog.spaziogis.it GEO+ geomatica in Italia http://bit.ly/GEOplus
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