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

Markus Metz markus.metz.giswork at gmail.com
Wed Dec 6 03:32:01 PST 2017

On Wed, Dec 6, 2017 at 10:41 AM, Markus Neteler <neteler at osgeo.org> wrote:
> # null file
> identical
> Curiosity: would it makes sense to compress the "nullcmpr" file according
to the selected compression? Probably Markus M had already explained it but
I don't remember...

In short, it's a waste of time.

Null files are very small with one bit per cell. Small data are difficult
to compress, and using a stronger compression method might actually produce
a larger, not a smaller output, and it takes longer. Regarding null file
compression, LZ4 is not only the fastest method, it is also regularly the
method with the best compression ratio.

Null files and [f]cell files have different characteristics regarding
compression, therefore one compression method can perform best for cell
values and another one might perform best for null file compression. You
would need to be able to choose separate compressors for the actual data
and the null file in order to achieve maximum compression or the best
compromise between speed and compression. That's too complicated. Most of
the time LZ4 is a good if not the best choice, therefore null file
compression is fixed to LZ4.

Markus M

> Best,
> markusN
> --
> Markus Neteler, PhD
> http://www.mundialis.de - free data with free software
> http://grass.osgeo.org
> http://courses.neteler.org/blog
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