Ubuntu Manpage: r.null - Manages NULL-values of given raster map.

NAME

       r.null  - Manages NULL-values of given raster map.

KEYWORDS

       raster, map management, null data, no-data

SYNOPSIS

       r.null
       r.null --help
       r.null  [-fincrz]  map=name  [setnull=val[-val][,val[-val],...]]   [null=float]   [--help]
       [--verbose]  [--quiet]  [--ui]

   Flags:
       -f
           Only do the work if the map is floating-point

       -i
           Only do the work if the map is integer

       -n
           Only do the work if the map doesn’t have a NULL-value bitmap file

       -c
           Create NULL-value bitmap file validating all data cells

       -r
           Remove NULL-value bitmap file

       -z
           Re-create NULL-value bitmap file (to compress or uncompress)

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       map=name [required]
           Name of raster map for which to edit null values

       setnull=val[-val][,val[-val],...]
           List of cell values to be set to NULL

       null=float
           The value to replace the null value by

DESCRIPTION

       The function of r.null is to explicitly create the NULL-value bitmap  file.  The  intended
       usage  is  to  update maps that do not have a NULL-value bitmap file (i.e. to indicate for
       each pixel if zero is a valid value or is to be considered as NULL, i.e. no  data  value).
       The module does not work with reclassified or external maps.

       The  design  is flexible. Ranges of values can be set to NULL and/or the NULL value can be
       eliminated and replace with a specified value.

       The setnull parameter is used to specify values in the ranges to be set to NULL.  A  range
       is  either  a  single value (e.g., 5.3), or a pair of values (e.g., 4.76-34.56).  Existing
       NULL-values are left NULL, unless the null argument is requested.

       The null parameter eliminates the NULL value and replaces it with value. This argument  is
       applied  only  to  existing  NULL  values,  and  not  to  the NULLs created by the setnull
       argument.

NOTES

Note that the value is restricted to integer if the map is an integer map.

r.null and reclassified maps
r.null does not support reclassified maps because, if r.null was run on the reclass raster
it would alter the original and any other reclass rasters of the original. Therefore
r.null does not allow recoding reclassified maps (products of r.reclass).
As a workaround, the way to recode such a map is: The user creates a raster map out of the
reclassified map by copying it:
r.mapcalc "newmap = reclass"

NULL data compression
By default no data files (i.e., NULL files) are not compressed unless a specific
environment variable is set. The NULL file compression must be explicitly turned on with
export GRASS_COMPRESS_NULLS=1.
Warning: such raster maps can then only be opened with GRASS GIS 7.2.0 or later. NULL file
compression can be managed with r.null -z.

External maps
From the r.external documentation: GDAL-linked (r.external) maps do not have or use a NULL
bitmap, hence r.null cannot manipulate them directly. Here NULL cells are those whose
value matches the value reported by the GDALGetRasterNoDataValue() function. To apply the
GDAL-linked the user need to either create a MASK (e.g. with r.mask) and then "apply" it
using e.g. r.resample, or use r.mapcalc to create a copy with the appropriate categories
changed to NULL (if() condition).

EXAMPLES

       Set specific values of a classified map to NULL:
       r.null map=landcover.30m setnull=21,22
       Set NULL-values of a map to a specific value:
       r.null map=fields null=99

AUTHOR

       U.S.Army Construction Engineering Research Laboratory

SOURCE CODE

       Available at: r.null source code (history)

       Accessed: Tuesday Jun 27 11:12:56 2023

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       © 2003-2023 GRASS Development Team, GRASS GIS 8.3.0 Reference Manual