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

Provided by: grass-doc_8.2.0-1build1_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 contraining 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: Mon Jun 13 15:11:03 2022

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