[GRASS-dev] disabling compression
glynn at gclements.plus.com
Wed Apr 25 08:01:12 EDT 2012
Benjamin Ducke wrote:
> According to the docs, GRASS_INT_ZLIB can be set to use
> LZW instead of RLE compression.
Actually, it's zlib's "deflate" (LZ77-based) compression; zlib was
created because LZW (which was used by the Unix "compress" utility)
was covered by patents at the time.
> But as far as I can see, there is not yet a way to completely
> prevent rasters from being compressed at creation time?
That's correct. IIUC, Maris is just suggesting that we have one
variable to select between no compression, RLE, and zlib, rather than
one variable to enable or disable compression and another to select
the compression algorithm.
The same principle can be applied to the implementation. Currently,
R__.compression_type will be either 1 (RLE) or 2 (zlib). Rather than
adding a separate R__.use_compression field, we can just set
R__.compression_type to 0 to indicate no compression. That is
consistent with the "compressed" field of the Cell_head structure.
Glynn Clements <glynn at gclements.plus.com>
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