.TH r.null 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBr.null\fR\fR  \- Manages NULL\-values of given raster map.
.SH KEYWORDS
raster, null data
.SH SYNOPSIS
\fBr.null\fR
.br
\fBr.null \-\-help\fR
.br
\fBr.null\fR [\-\fBfincrz\fR] \fBmap\fR=\fIname\fR  [\fBsetnull\fR=\fIval[\-val]\fR[,\fIval[\-val]\fR,...]]   [\fBnull\fR=\fIfloat\fR]   [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-f\fR" 4m
.br
Only do the work if the map is floating\-point
.IP "\fB\-i\fR" 4m
.br
Only do the work if the map is integer
.IP "\fB\-n\fR" 4m
.br
Only do the work if the map doesn\(cqt have a NULL\-value bitmap file
.IP "\fB\-c\fR" 4m
.br
Create NULL\-value bitmap file validating all data cells
.IP "\fB\-r\fR" 4m
.br
Remove NULL\-value bitmap file
.IP "\fB\-z\fR" 4m
.br
Re\-create NULL\-value bitmap file (to compress or uncompress)
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBmap\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of raster map for which to edit null values
.IP "\fBsetnull\fR=\fIval[\-val][,\fIval[\-val]\fR,...]\fR" 4m
.br
List of cell values to be set to NULL
.IP "\fBnull\fR=\fIfloat\fR" 4m
.br
The value to replace the null value by
.SH DESCRIPTION
The function of \fIr.null\fR 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.
.PP
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.
.PP
The \fBsetnull\fR 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.
.PP
The \fBnull\fR 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.
.SH NOTES
Note that the value is restricted to integer if the map is an integer map.
.SS r.null and reclassified maps
\fIr.null\fR does not support reclassified maps because, if \fIr.null\fR
was run on the reclass raster it would alter the original and any other
reclass rasters of the original.  Therefore \fIr.null\fR does not allow
recoding reclassified maps (products of \fIr.reclass\fR).
.br
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:
.br
.br
.nf
\fC
r.mapcalc \(dqnewmap = reclass\(dq
\fR
.fi
.SS 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.
.br
Warning: such raster maps can then only be opened with GRASS GIS 7.2.0 or
later. NULL file compression can be managed with \fBr.null \-z\fR.
.SS External maps
From the r.external documentation: GDAL\-linked
(\fIr.external\fR) maps do not have or use a NULL bitmap, hence \fIr.null\fR 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 \fIr.mask\fR) and
then \(dqapply\(dq it using e.g. \fIr.resample\fR, or use \fIr.mapcalc\fR to create a copy
with the appropriate categories changed to NULL (if() condition).
.SH EXAMPLES
Set specific values of a classified map to NULL:
.br
.br
.nf
\fC
r.null map=landcover.30m setnull=21,22
\fR
.fi
Set NULL\-values of a map to a specific value:
.br
.br
.nf
\fC
r.null map=fields null=99
\fR
.fi
.SH SEE ALSO
\fI
r.compress,
r.support,
r.quant
\fR
.SH AUTHOR
U.S.Army Construction Engineering Research Laboratory
.SH SOURCE CODE
.PP
Available at: r.null source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual