NAME

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

KEYWORDS

       raster, null 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

SEE ALSO

        r.compress, r.support, r.quant

AUTHOR

       U.S.Army Construction Engineering Research Laboratory

SOURCE CODE

       Available at: r.null source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual