[GRASS-dev] GRASS GIS raster files: LZW compression?

[Even Rouault]

On jeudi 26 octobre 2017 18:57:10 CEST Markus Neteler wrote:
> On Thu, Oct 26, 2017 at 9:25 AM, Markus Metz
> 
> <markus.metz.giswork at gmail.com> wrote:
> > On Wed, Oct 25, 2017 at 10:40 PM, Markus Neteler <neteler at osgeo.org> wrote:
> >> Hi devs,
> >> 
> >> while playing with the SRTM 30m world I see that there is a difference
> >> of 66GB in size between LZ4 (larger) and DEFLATE (smaller). While this
> >> is not a surprise I was wondering if LZW compression could be brought
> >> back. AFAIK the license issue is gone for a while and indeed GRASS got
> >> a special permit back in 1988 according to the old source code.
> >> 
> >> Would that make sense?
> > 
> > You could test with compress (LZW) and gzip (DEFLATE based on LZ77) if
> > that
> > would make sense.
> > 
> > Implementation would be a bit of an effort: either adapt from the source
> > code of compress or from GDAL's LZW compression for Tiff.
> 
> I thought to remember that the LZW compression was in libgis some
> decades ago but did not find any trace so far.
> At that point I happily abandon this idea - no need to waste energy here :-)

Another option would be to consider the zstd / zstandard compression method
( https://github.com/facebook/zstd ), that has roughly the compression ratio of DEFLATE / 
LZ77 with a compression and decompression speed 3 or 4 times faster. This is in my todo list 
of things to experiment as a libtiff compression method.

Zstd has been added recently as a compression method in the Linux kernel:
https://www.phoronix.com/scan.php?page=news_item&px=ZSTD-Linux-Kernel-Image

Even

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