This is the command r.nullgrass that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator
PROGRAM:
NAME
r.null - Manages NULL-values of given raster map.
KEYWORDS
raster, null data
SYNOPSIS
r.null
r.null --help
r.null [-fincr] 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
--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 fix "old" maps that don’t have a NULL-value bitmap file (i.e. to indicate if
zero is valid value or is to be converted to NULL). The module does not work with
reclassified 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.
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
NOTES
Note that value is restricted to integer if the map is an integer map.
r.null and reclassified maps:
The problem is, 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 doesn’t allow recoding
reclassified maps (products of r.reclass).
So, the way to recode such a map is: The user makes a raster out of the reclass that isn’t
a reclass by copying it:
r.mapcalc newmap = reclass
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