I've extracted a subset from the original ASCII: https://dl.dropboxusercontent.com/u/13861666/FI_clipped.asc I'm obtaining the same behaviour, so it can be a test case.
giovanni 2014-07-05 21:43 GMT+02:00 G. Allegri <[email protected]>: > 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 > -- 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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