[GRASS-user] Best format for exporting raster data

Glynn Clements glynn at gclements.plus.com
Wed Sep 1 13:45:12 EDT 2010

Rainer M Krug wrote:

> It would be nice, if grass would be able to deal with on-the-fly
> decompression - not from a .tar.gz file, but from gz compressed files.

GRASS rasters are already compressed by default, either using RLE or
zlib compression (OTOH, the null bitmap isn't compressed; that will
cease to be an issue if we embed nulls into the raster data).

But GRASS doesn't generally read data from files per se, but from
either the GRASS "database" or from GDAL (and the former might
eventually go away if we can get "native" GRASS support into GDAL).

The main issue with on-the-fly decompression using general-purpose
formats is that rasters aren't guaranteed to be read sequentially,
while compression algorithms require sequential access.

Similarly, while there exist filesystems which can mount archives, tar
files (and especially compressed tar files) are a poor choice, as they
are designed for sequential access. ZIP/RAR are more suited to such

Ultimately, I don't think that this situation is common enough to be
worth doing anything about. If you want to access archived data, you
just unpack the archives first (or use an archive format which can be

Glynn Clements <glynn at gclements.plus.com>

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