Ubuntu Manpage: r.mask - Creates a MASK for limiting raster operation.

Provided by: grass-doc_8.3.2-1ubuntu2_all

NAME

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

KEYWORDS

       raster, mask, null data, no-data

SYNOPSIS

       r.mask
       r.mask --help
       r.mask   [-ir]    [raster=name]     [maskcats=string]     [vector=name]    [layer=string]    [cats=range]
       [where=sql_query]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -i
           Create inverse mask

       -r
           Remove existing mask (overrides other options)

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       raster=name
           Name of raster map to use as mask

       maskcats=string
           Raster values to use for mask
           Format: 1 2 3 thru 7 *
           Default: *

       vector=name
           Name of vector map to use as mask
           Or data source for direct OGR access

       layer=string
           Layer number or name (vector)
           Vector features can have category values in different layers. This number determines which  layer  to
           use. When used with direct OGR access this is the layer name.
           Default: 1

       cats=range
           Category values (vector)
           Example: 1,3,7-9,13

       where=sql_query
           WHERE conditions of SQL statement without ’where’ keyword (vector)
           Example: income < 1000 and population >= 10000

DESCRIPTION

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

       The MASK is applied when reading an existing GRASS raster map, for example when used as an input map in a
       module.  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 boundaries 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.

       By default, r.mask converts any non-NULL value in the input map, including zero, to 1.  All  these  areas
       will  be  part of the MASK (see the notes for more details). To only convert specific values (or range of
       values) to 1 and the rest to NULL, use the maskcats parameter.

       Because the MASK created with r.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. To remove a mask and restore raster operations to normal (i.e., all cells  of  the
       current  region),  remove the MASK by setting the -r remove MASK flag (r.mask -r).  Alternatively, a mask
       can be removed using g.remove or by renaming it to any other name with g.rename.

NOTES

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 file is removed.

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). Note that the maskcats can only be used if the input map is an integer map.

Different ways to create a MASK
The r.mask function creates a MASK with values 1 and NULL. But note that a MASK can also be created using
other functions that have a raster as output, by naming the output raster ’MASK’. Such layers could have
other values than 1 and NULL. The user should therefore be aware that grid cells in the MASK map
containing NULL or 0 will replace data with NULL, while cells containing other values will allow data to
pass through unaltered. This means that:

If a binary map with [0,1] values is used as input in r.mask, all raster cells with 0 and 1 will be part
of the MASK. This is because r.mask converts all non-NULL cells to 1.
r.mapcalc -s "map1 = round(rand(0,1))"
r.mask raster=map1
On the other hand, if a binary map is used as an input in g.copy to create a MASK, only the raster cells
with value 1 will be part of the MASK.
r.mapcalc -s "map2 = round(rand(0,1))"
g.copy raster=map2,MASK

Handling of floating-point maps
r.mask treats floating-point maps the same as integer maps (except that floating maps are not allowed in
combination with the maskcats parameter); all non-NULL values of the input raster map are converted to 1
and are thus part of the MASK. In the example below, all raster cells are part of the MASK, i.e., nothing
is blocked out from analysis and/or display.
r.mapcalc -s "map3 = rand(0.0,1.0)"
r.mask raster=map3
However, when using another method than r.mask to create a mask, the user should be aware that the MASK
is read as an integer map. If MASK is 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.mapcalc -s "map4 = rand(0.0,1.0)"
g.copy raster=map4,MASK
In the example above, raster cells with a rounded value of 1 are part of the MASK, while raster cells
with a rounded value of 0 are converted to NULL and consequently blocked out from analysis and/or
display.

EXAMPLES

       The examples are based on the North Carolina sample dataset.

       Create a raster mask, for constraining the calculation of univariate statistics of the  elevation  values
       for "lakes":
       # set computation region to lakes raster map
       g.region raster=lakes -p
       # use lakes as MASK
       r.mask raster=lakes
       # get statistics for elevation pixels of lakes:
       r.univar elevation
       Remove the raster mask ("MASK" map) with the -r flag:
       r.mask -r
       Creating a mask from selected categories in the North Carolina ’geology_30m’ raster map:
       g.region raster=geology_30m -p
       r.category geology_30m
       d.mon wx0
       d.rast geology_30m
       r.mask raster=geology_30m maskcats="217 thru 720"
       d.mon wx0
       d.rast geology_30m

AUTHOR

       Michael Barton, Arizona State University

SOURCE CODE

       Available at: r.mask source code (history)

       Accessed: Monday Apr 01 03:09:29 2024

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       © 2003-2024 GRASS Development Team, GRASS GIS 8.3.2 Reference Manual

GRASS 8.3.2                                                                                       r.mask(1grass)