news

GRASS GIS 5.0 LZW compression deprecated

Important change information for GRASS 5.0 beta 11 (and later) users


This will affect all GRASS 5 versions later than beta10 (CVS was updated Jan 18 2001)

Because of the UNISYS patent (http://www.unisys.com/unisys/lzw/) on the LZW compression algorithm, on January 18 2001, GRASS 5 library code no longer uses this method to compress floating point rasters and G3D files. Unfortunately, this creates an incompatible change for persons using earlier versions of GRASS 5.0 (GRASS 5 beta1 to beta10 users).

Note: This LZW removal does NOT affect

  • GRASS 5 CELL type raster maps or
  • Persons just now upgrading from GRASS 4.x. (GRASS 4.x was not using LZW) to GRASS 5beta11 or later.

How to migrate your GRASS 5 floating point raster maps:

Generally the conversion is a two-step procedure (see below for one step):

  1. Before installing newer GRASS libraries and binaries (beta11 and later) you must uncompress all floating point raster maps. Again: In order to make your data readable you must uncompress all floating point rasters before installing newer GRASS libraries and binaries. The command “r.compress -u” will do the job (see below for a script to assist).
  2. After installing the new binaries you may recompress your rasters with “r.compress” which will use the DEFLATE method available in libz (zlib) (this compression library is usually installed by default on your system, otherwise install it).

How to migrate your GRASS 5 G3D raster voxel maps:

  • Unfortunately, any LZW compressed G3D files must be dumped with r3.out.ascii, and then reimported with r3.in.ascii.

The GRASS 5.0 Development Team apologizes for this inconvenience.


We provide two ways to convert your data:

1. Two-step conversion: Requires old and new GRASS.

  • fp_uncompress.sh: uncompress all raster maps. Save and run within your old GRASS 5:   sh fp_uncompress.sh This scripts will decompress all maps within a location.

    Run this within all locations you have!

  • Finished with all GRASS 5 locations you have? O.k., now upgrade to the non-LZW GRASS 5 (beta11 or later as well as GRASS CVS version).

  • fp_recompress.sh: recompress all raster maps with DEFLATE. Save and run within new GRASS 5: sh fp_recompress.sh This scripts will compress back all maps within a location in zlib/flate compression.

That’s it. Welcome to the patent-free GRASS 5.

2. One-step conversion: Does not require old GRASS, simply run in new GRASS 5beta11 (or later). So you don’t need the old GRASS 5:

   r.lzw2z changes the compression on-the-fly within the new GRASS 5.0beta11 (or later):


Proceed to Download latest GRASS 5.0.x

So: Did you read above? Did you download r.lzw2z or the fp_*.sh scripts if you are already using GRASS 5? If so, please proceed:


Jan 18 2001, © GRASS Development Team, last update: June 12, 2001