[GRASS-dev] Testing the new ZSTD raster compression - was: Re: GRASS GIS raster files: LZW compression?

[Markus Metz]

On Sun, Jun 10, 2018 at 8:44 PM, Nikos Alexandris <nik at nikosalexandris.net>
wrote:
>
>
> Nikos:
>
>>> I am building a docker image, based on trunk, for which I need to ensure
>>> that ZSTD is the default compressor.
>>>
>>> What is the way to pre-set this at the configuration step, before
>>> compiling, so as to avoid to take care about it later on by setting
>>> GRASS_COMPRESSOR?
>
>
> Markus M:
>
>> ZSTD is already the default compressor if available, no further settings
>> needed.
>
>
> Great!
>
> However, descriptions of compressors in the raster indroduction for
> trunk [0], are maybe confusing.
>
> ```
> ZLIB
> ZLIB's deflate is the default compression method for all raster maps.
> ```
>
> and
>
> ```
> ZSTD
> ... ZSTD is the recommended default compression method.
> ```
>
> The same piece of text is used for `r.compress` [1].
> [0] https://grass.osgeo.org/grass75/manuals/rasterintro.html
> [1] https://grass.osgeo.org/grass75/manuals/r.compress.html
>
> I realised this before commenting in #3499. Yet, I thought "default" is
ZLIB, and "recommended default" (like: "dear user,
> it's best if you set ZSTD as the default") is ZSTD.

It's trunk, and a new feature is being tested in trunk, therefore I made it
the default compression method if available. I was not sure if ZSTD should
become the new default compression if available, but after creating
thousands of raster maps with ZSTD compression on different systems, I
think it is safe to make ZSTD the new default if available. The rasterintro
and the manual for r.compress have been updated accordingly in trunk r72794.

ZSTD is by now widely used by many different projects, also by GDAL.
Considering the performance improvement of ZSTD over ZLIB, it is worth to
consider if ZSTD should become a requirement for the next minor release
(GRASS 7.6), granted that ZSTD is available on all supported systems.

Markus M
>
> Nikos
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