table of contents
r.null(1grass) | GRASS GIS User's Manual | r.null(1grass) |
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
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: Saturday Jul 27 17:08:14 2024
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