[GRASS5] 5.7: make GRASS_INT_ZLIB default?

[Markus Neteler]

On Fri, Nov 19, 2004 at 06:02:25PM +0000, Glynn Clements wrote:
> 
> Markus Neteler wrote:
> 
> > proposal for 5.7-CVS: make zlib compression instead of RLE the
> > default setting, probably modifying:
> > 
> > grass57/lib/gis > grep GRASS_INT_ZLIB *
> > opencell.c:     COMPRESSION_TYPE = getenv("GRASS_INT_ZLIB") ? 2 : 1;
> > 
> > Are there objections?
> 
> The most obvious problem is that raster maps will be unreadable on
> versions of GRASS which pre-date the addition of zlib support.
> 
> Also, I don't know whether that feature has received any significant
> testing.

Here some numbers:

LANDSAT-7 scene:

- compression at 50% of the standard GRASS CELL file compression
  57MB color channel -> 28 MB with ZLIB
  233MB panchromatic channel -> 127 MB with ZLIB

This is quite an advantage when dealing with lots of remote sensing
data.

- display time (over NFS network in both cases):
  beforehand: g.region rast=channel
 
  time d.rast color_channel_standard_compression
   real    0m8.957s
   user    0m4.850s
   sys     0m0.230s

  time d.rast color_channel_zlib_compression
   real    0m6.011s
   user    0m5.080s
   sys     0m0.170s
 
 ########
  time d.rast pan_channel_standard_compression
   real    0m11.500s
   user    0m10.690s
   sys     0m0.210s

  time d.rast pan_channel_zlib_compression
   real    0m11.421s
   user    0m10.800s
   sys     0m0.210s

Interestingly there is less difference the larger the map.

Markus