r.null(1grass) GRASS GIS User's Manual r.null(1grass)
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 re-
classified 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 di-
rectly. Here NULL cells are those whose value matches the value re-
ported 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)
Accessed: unknown
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