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       r.mask  - Creates a MASK for limiting raster operation.


       raster, mask


       r.mask help
       r.mask [-ior]  [input=string]   [maskcats=string]   [--verbose]  [--quiet]

           Create inverse MASK from specified 'maskcats' list

           Overwrite existing MASK

           Remove existing MASK (overrides other options)

           Verbose module output

           Quiet module output

           Raster map to use as MASK

           Category values to use for MASK (format: 1 2 3 thru 7 *)
           Default: *


       r.mask - Facilitates creation of a raster "MASK" map to control raster operations.

       The  MASK is only applied when reading an existing GRASS raster map, for example when used
       in a module as an input map.  The MASK will block out certain areas of a raster  map  from
       analysis  and/or display, by "hiding" them from sight of other GRASS modules. Data falling
       within the bounaries of the MASK can be modified and operated upon by other  GRASS  raster
       modules; data falling outside the MASK is treated as if it were NULL.

       Because  the  MASK is actually only a reclass map named "MASK", it can be copied, renamed,
       removed, and used in analyses, just like other GRASS raster map layers.  The  user  should
       be  aware  that  a  MASK  remains in place until a user renames it to something other than
       "MASK", or removes it using "r.mask -r" or g.remove.

       Grid cells in the MASK map containing 0 or NULL will replace data with NULL,  while  cells
       containing other values will allow data to pass through unaltered.

       To restore raster operations to normal (i.e., all cells of the current region), remove the
       MASK map by setting the -r remove MASK flag. In this case, a  dummy  value  must  also  be
       given  for  the  input  parameter.   A  MASK  also  can be removed by using g.remove or by
       renaming it to any other name with g.rename.


       The above method for specifying a "mask" may seem counterintuitive.  Areas inside the MASK
       are not hidden; areas outside the MASK will be ignored until the MASK map is removed.

       The  mask  is read as an integer map. If MASK is actually a floating-point map, the values
       will be converted to integers using the map's quantisation rules (this defaults to  round-
       to-nearest, but can be changed with r.quant).

       r.mask  uses  r.reclass to create a reclassification of an existing raster map and name it
       MASK. A reclass map takes up less space, but is affected by any changes to the  underlying
       map  from which it was created.  The user can select category values from the input raster
       to use in the MASK with the maskcats parameter; if r.mask is run from  the  command  line,
       the category values listed in maskcats must be quoted (see example below).

       Somewhat  similar  program  functions  to  those  performed  by  r.mask  can be done using
       r.mapcalc, g.region, and other commands.


       Creating a raster MASK, for showing only elevations of lakes:
       r.mask input=lakes
       # statistics only for elevation pixels in the lakes:
       r.univar elevation
        Removing a raster MASK with the -r flag:
       r.mask -r
        Creating a MASK from categories 3 through 6 in the North  Carolina  ’geology_30m'  raster
       g.region rast=geology_30m -p
       r.category geology_30m
       d.mon x0
       d.rast geology_30m
       r.mask input=geology_30m maskcats="217 thru 720"
       d.rast geology_30m


        g.region, r.mapcalc, r.reclass, g.remove, g.rename


       Michael Barton, Arizona State University

       Last changed: $Date: 2012-02-22 11:36:23 -0800 (Wed, 22 Feb 2012) $

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