On Tue, Sep 6, 2016 at 1:44 PM, Markus Neteler <nete...@osgeo.org> wrote: > Hi, > > since my local drive was filled up again :) I checked raster how data are > currently compressed in GRASS GIS 7.2.svn. > According to > > https://grass.osgeo.org/grass72/manuals/r.compress.html#used-compression-algorithms > > all maps are DEFLATE compressed by default: > > "Raster maps are by default ZLIB compressed. > ... > > Floating point (FCELL, DCELL) raster maps never use RLE compression; they > are either compressed with ZLIB, LZ4, BZIP2 or are uncompressed. > " > > Ehm, now how *are* FCELL, DCELL compressed by default? Not quite clear to > me! This document needs improvements.
The manual says, as you cited: "Raster maps are by default ZLIB compressed." What exactly is unclear about this? Should it say "All raster maps ..." ? > > Reality check with Sentinel-2 data (3 different bands, same regional > extent): > > GRASS 7.2.svn (utm37n):~ > r.info -r s2_20151225_B02_10m > min=0 > max=22937 > GRASS 7.2.svn (utm37n):~ > r.info -r s2_20151225_B04_10m > min=0 > max=18849 > GRASS 7.2.svn (utm37n):~ > r.info -r s2_20151225_B8A_20m > min=0 > max=17210 > > GRASS 7.2.svn (utm37n):~ >:~ > r.compress s2_20151225_B02_10m -p > <s2_20151225_B02_10m> is compressed (method 2: ZLIB). Data type: > CELL > > GRASS 7.2.svn (utm37n):~ >:~ > r.compress s2_20151225_B04_10m -p > <s2_20151225_B04_10m> is compressed (method 2: ZLIB). Data type: > CELL > > GRASS 7.2.svn (utm37n):~ >:~ > r.compress s2_20151225_B8A_20m -p > <s2_20151225_B8A_20m> is compressed (method 2: ZLIB). Data type: > CELL > > So far so nice. Now the suprising part, while the channels are not identical > (obviously, since covering different spectral parts), the map sizes are > identical! > > GRASS 7.2.svn (utm37n):~ > ls -la > ... > -rw-r--r-- 1 neteler neteler 2539235691 Jun 14 17:14 s2_20151225_B02_10m > -rw-r--r-- 1 neteler neteler 2539235691 Jun 14 17:19 s2_20151225_B03_10m > -rw-r--r-- 1 neteler neteler 2539235691 Jun 14 17:25 s2_20151225_B04_10m > -rw-r--r-- 1 neteler neteler 634878630 Jun 14 20:36 s2_20151225_B05_20m > -rw-r--r-- 1 neteler neteler 634878630 Jun 14 20:37 s2_20151225_B06_20m > -rw-r--r-- 1 neteler neteler 634878630 Jun 14 20:39 s2_20151225_B07_20m > -rw-r--r-- 1 neteler neteler 634878630 Jun 14 20:40 s2_20151225_B11_20m > -rw-r--r-- 1 neteler neteler 634878630 Jun 14 20:42 s2_20151225_B12_20m > -rw-r--r-- 1 neteler neteler 634878630 Jun 14 20:43 s2_20151225_B8A_20m > > I would expect different sizes, compression can hardly lead to identical > file sizes. The default ZLIB compression level was invalid, causing ZLIB to not compress at all. Fixed in r69387,8. Markus M > > Next test: gzip the file > > GRASS 7.2.svn (utm37n):~/grassdata/utm37n/PERMANENT/cell > ls -la > s2_20151225_B03_10m > -rw-r--r-- 1 mneteler mneteler 2539235691 Jun 14 17:19 s2_20151225_B03_10m > > GRASS 7.2.svn (utm37n):~/grassdata/utm37n/PERMANENT/cell > gzip > s2_20151225_B03_10m > > GRASS 7.2.svn (utm37n):~/grassdata/utm37n/PERMANENT/cell > ls -la > s2_20151225_B03_10m.gz > -rw-r--r-- 1 mneteler mneteler 1456248453 Jun 14 17:19 > s2_20151225_B03_10m.gz > > R >> 1456248453/2539235691 > [1] 0.5734987 > > Quite smaller! So I am not at all convinced that these CELL files are > currently ZLIB compressed. Compressing a whole file instead of compressing each row separately (GRASS reads and writes raster data row by row) can lead to higher compression ratios. > > From this ticket I would expect something else: > https://trac.osgeo.org/grass/ticket/2349 > > Ah, and no specific environment variables are set: > > GRASS 7.2.svn (utm37n):~ > echo $GRASS_<tab> > $GRASS_ADDON_BASE $GRASS_GNUPLOT $GRASS_HTML_BROWSER $GRASS_PAGER > $GRASS_PROJSHARE $GRASS_PYTHON $GRASS_VERSION > > > A bug? > > Markus > > _______________________________________________ > grass-dev mailing list > grass-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-dev _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-dev