[GRASS-dev] [GRASS GIS] #2349: CELL raster format: make ZLIB level 3 standard compression instead of RLE

[GRASS GIS]

#2349: CELL raster format: make ZLIB level 3 standard compression instead of RLE
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 Reporter:  neteler                  |       Owner:  grass-dev@…              
     Type:  enhancement              |      Status:  new                      
 Priority:  blocker                  |   Milestone:  7.0.0                    
Component:  Raster                   |     Version:  svn-releasebranch70      
 Keywords:  compression, r.compress  |    Platform:  All                      
      Cpu:  Unspecified              |  
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Comment(by glynn):

 Replying to [comment:12 neteler]:

 > It seems that the NULL file is not compressed (file "cell_misc/null").
 According to
 >
 > http://lists.osgeo.org/pipermail/grass-user/2010-January/054216.html
 >
 > it is one bit (null/non-null) for each cell.

 > Question: Would it be possible to compress also the null files, even
 with just a
 > weak compression?

 Being uncompressed, the null files don't contain an index. The offset to
 the beginning of a given row is obtained by multiplying the row number by
 the number of bytes per row (which is just the number of columns divided
 by 8, rounded upwards).

 The main issue is likely to be the need to support both formats. We need
 to

  * Be able to read and write the uncompressed format, for compatibility
 with existing versions of GRASS.
  * Be able to distinguish between compressed and uncompressed formats on
 read.
  * Provide some mechanism (i.e. yet another environment variable) to
 indicate which format to use on write.

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Ticket URL: <http://trac.osgeo.org/grass/ticket/2349#comment:13>
GRASS GIS <http://grass.osgeo.org>