[GRASS-dev] NULL file compression: loop over uncompressed maps to save disk space

[Markus Metz]

On Wed, Jan 11, 2017 at 12:37 PM, Markus Neteler <neteler at osgeo.org> wrote:
>
> On Wed, Jan 11, 2017 at 10:34 AM, Markus Metz
> <markus.metz.giswork at gmail.com> wrote:
> > On Tue, Jan 3, 2017 at 6:08 PM, Markus Neteler <neteler at osgeo.org>
wrote:
> ...
> >> Questions:
> >> I believe that an additional -g flag for shell style printing would be
> >> useful as well).
> >> Maybe with a -g flag no need to use the stderr redirect?
> >> Any better ideas here? (if yes, feel free to submit to SVN for testing)
> >
> > I have added your changes and a new shell style option to trunk in
r70337.
>
> Thanks for that!
>
> > Note that this is not standard shell style because the module accepts
> > several input maps, thus compression info is written to stdout as one
line
> > per input map. The format is
> > input map name|data type|name of data compression method|NULL file
> > compression
> > e.g.
> > eu_dem25|FCELL|ZLIB|NO
> > or
> > eu_dem25|FCELL|BZIP2|YES
>
> Yes, that's quite useful like this. Maybe a small modification to make
> it usable for the beloved eval() function?
>
> r.compress -g eu_dem25
> eu_dem25=FCELL|ZLIB|YES
> ?

In this case, eu_dem25 would be both the name of a raster map and the name
of a variable, I find this confusing. And you still need to split the
result. I guess parsing
eu_dem25|FCELL|ZLIB|YES
would be slightly easier in python than
eu_dem25=FCELL|ZLIB|YES

> This would keep the -g implementations consistent across different
commands.

Full easy support for eval() is not possible if the same parameters are
printed several times. See e.g. r.univar -gt with a zonal map, r.quantile,
r.stats.quantile or v.db.connect -g with several connections defined.
Therefore I would use one line with name=value where possible, otherwise
one line per input with separated fields. I would not mix the two, IMHO it
will cause confusion.

>
> That old "null2" name is also here:
>
> ./raster/r.support/main.c:    G_file_name_misc(path, "cell_misc",
> "null2", raster->answer, G_mapset());

Fixed in r70340,1 (trunk, relbr72).

Markus M
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