I've debugged it, and it gets Float64 directly from GDALGetRasterDataType( GDALRasterBandH ). I've also tried opening it with Python GDAL and I get Float64. gdalinfo tells me Float32. I will try to send you a subset of it. It's not easy, as it is a heavy ASCII Grid and I don't want to alter it.
giovanni 2014-07-05 20:22 GMT+02:00 Even Rouault <even.roua...@mines-paris.org>: > Le samedi 05 juillet 2014 20:18:50, G. Allegri a écrit : > > 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.... > > If gdalinfo opens it as Float32, then it is Float32 for everybody. I guess > QGIS probably promotes Float32 to Float64. > > > > > giovanni > > > > 2014-07-05 18:53 GMT+02:00 G. Allegri <gioha...@gmail.com>: > > > 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 <even.roua...@mines-paris.org > >: > > > > > > 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 > > -- > 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
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