[GRASS-dev] Re: disabling compression

Glynn Clements glynn at gclements.plus.com
Thu Apr 26 16:16:28 EDT 2012

Jim Regetz wrote:

> However, the existing GRASS_INT_ZLIB variable only applies to integer 
> rasters, correct?

Correct. FP rasters never use RLE; they're either compressed with zlib
or uncompressed.

> Although in all cases this variable does indeed 
> dictate whether the Cell_head "compressed" field is set to 1 or 2, 
> AFAICT put_fp_data ignores it and uses zlib for writing compressed 
> floating point rasters in either case. Is this intentional?

Yes. RLE probably wouldn't provide useful compression for FP rasters.

If a single variable was used for both integer and FP rasters, the
logical semantics would be:

	value	compression
		integer	float

	0	none	none
	1	RLE	zlib
	2	zlib	zlib

Glynn Clements <glynn at gclements.plus.com>

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