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@@ -279,12 +279,16 @@ The GRASS GIS raster format is architecture independent and portable between
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<h3>Raster compression</h3>
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<h3>Raster compression</h3>
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<!-- keep in sync with raster/r.compress/r.compress.html -->
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-
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All GRASS GIS raster map types are by default ZLIB compressed, i.e. using
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All GRASS GIS raster map types are by default ZLIB compressed, i.e. using
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ZLIB's deflate algorithm. Through the environment variable
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ZLIB's deflate algorithm. Through the environment variable
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<tt>GRASS_COMPRESSOR</tt> the compression method can be set to RLE, ZLIB,
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<tt>GRASS_COMPRESSOR</tt> the compression method can be set to RLE, ZLIB,
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LZ4, or BZIP2.
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LZ4, or BZIP2.
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<p>
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<p>
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+Important: the NULL file compression must be explicitly turned on with
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+<tt>export GRASS_COMPRESS_NULLS=1</tt> - such raster maps can then only
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+be opened with GRASS GIS 7.2.0 or later. NULL file compression can be
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+managed with <b>r.null -z</b>.
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+<p>
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Integer (CELL type) raster maps can be compressed with RLE if
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Integer (CELL type) raster maps can be compressed with RLE if
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the environment variable <tt>GRASS_INT_ZLIB</tt> exists and is set to value
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the environment variable <tt>GRASS_INT_ZLIB</tt> exists and is set to value
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0. However, this is not recommended.
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0. However, this is not recommended.
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Markus Neteler