This question is better addressed to the QGis-dev list as QGis is promoting the Float32 type to be Float64 type
https://github.com/qgis/QGIS/blob/master/src/providers/gdal/qgsgdalprovider.cpp#L1103 Jul 5, 2014, at 3:43 PM, "G. Allegri" <[email protected]> wrote: > ldd tells me that both QGIS and gdalinfo point to the same gdal libs > > ldd /usr/bin/qgis.bin | grep gdal > libgdal.so.1 => /usr/lib/libgdal.so.1 (0x0284b000) > > ldd /usr/bin/gdalinfo | grep gdal > libgdal.so.1 => /usr/lib/libgdal.so.1 (0x00c5f000) > > But I must correct about Python. Running it against the right modules it > reports raster band data type as GDT_Float32. > > In QGIS Float64 comes out here: > https://github.com/qgis/QGIS/blob/master/src/providers/gdal/qgsgdalprovider.cpp#L1076 > > giovanni > > > > > 2014-07-05 21:02 GMT+02:00 Even Rouault <[email protected]>: > Le samedi 05 juillet 2014 20:35:45, G. Allegri a écrit : > > Given that an ASCII Grid doesn't provide a data type, maybe the driver > > choose the larger one, while the utilities guess it trying to fit the > > values into a smaller type? > > No, GDAL does not do that sort of magic. Are you sure the GDAL version used by > Python is the same as by the utilities ? > > > > > giovanni > > > > 2014-07-05 20:31 GMT+02:00 G. Allegri <[email protected]>: > > > 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 <[email protected]>: > > > > > > 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 <[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 > > >> > > >> -- > > >> 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 > _______________________________________________ > gdal-dev mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/gdal-dev
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