1r.null(1)                   GRASS GIS User's Manual                  r.null(1)
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NAME

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

9       raster, null data
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SYNOPSIS

12       r.null
13       r.null --help
14       r.null    [-fincrz]    map=name     [setnull=val[-val][,val[-val],...]]
15       [null=float]   [--help]  [--verbose]  [--quiet]  [--ui]
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17   Flags:
18       -f
19           Only do the work if the map is floating-point
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21       -i
22           Only do the work if the map is integer
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24       -n
25           Only do the work if the map doesn’t have a NULL-value bitmap file
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27       -c
28           Create NULL-value bitmap file validating all data cells
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30       -r
31           Remove NULL-value bitmap file
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33       -z
34           Re-create NULL-value bitmap file (to compress or uncompress)
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36       --help
37           Print usage summary
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39       --verbose
40           Verbose module output
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42       --quiet
43           Quiet module output
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45       --ui
46           Force launching GUI dialog
47
48   Parameters:
49       map=name [required]
50           Name of raster map for which to edit null values
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52       setnull=val[-val][,val[-val],...]
53           List of cell values to be set to NULL
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55       null=float
56           The value to replace the null value by
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DESCRIPTION

59       The function of r.null is to explicitly create  the  NULL-value  bitmap
60       file.  The  intended  usage  is  to  update  maps  that  do  not have a
61       NULL-value bitmap file (i.e. to indicate for each pixel if  zero  is  a
62       valid  value  or  is to be considered as NULL, i.e. no data value). The
63       module does not work with reclassified or external maps.
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65       The design is flexible. Ranges of values can be set to NULL and/or  the
66       NULL value can be eliminated and replace with a specified value.
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68       The setnull parameter is used to specify values in the ranges to be set
69       to NULL.  A range is either a single value (e.g., 5.3), or  a  pair  of
70       values  (e.g., 4.76-34.56).  Existing NULL-values are left NULL, unless
71       the null argument is requested.
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73       The null parameter eliminates the  NULL  value  and  replaces  it  with
74       value.  This  argument is applied only to existing NULL values, and not
75       to the NULLs created by the setnull argument.
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NOTES

78       Note that the value is restricted to integer if the map is  an  integer
79       map.
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81   r.null and reclassified maps
82       r.null does not support reclassified maps because, if r.null was run on
83       the reclass raster it would alter the original and  any  other  reclass
84       rasters  of  the  original.   Therefore  r.null does not allow recoding
85       reclassified maps (products of r.reclass).
86       As a workaround, the way to recode such a map is: The  user  creates  a
87       raster map out of the reclassified map by copying it:
88       r.mapcalc "newmap = reclass"
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90   NULL data compression
91       By default no data files (i.e., NULL files) are not compressed unless a
92       specific environment variable is set. The NULL file compression must be
93       explicitly turned on with export GRASS_COMPRESS_NULLS=1.
94       Warning:  such raster maps can then only be opened with GRASS GIS 7.2.0
95       or later. NULL file compression can be managed with r.null -z.
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97   External maps
98       From the r.external documentation: GDAL-linked (r.external) maps do not
99       have  or  use  a  NULL  bitmap,  hence  r.null  cannot  manipulate them
100       directly. Here NULL cells are  those  whose  value  matches  the  value
101       reported  by  the  GDALGetRasterNoDataValue()  function.  To  apply the
102       GDAL-linked the user need to either create a MASK  (e.g.  with  r.mask)
103       and then "apply" it using e.g. r.resample, or use r.mapcalc to create a
104       copy with the appropriate categories changed to NULL (if() condition).
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EXAMPLES

107       Set specific values of a classified map to NULL:
108       r.null map=landcover.30m setnull=21,22
109       Set NULL-values of a map to a specific value:
110       r.null map=fields null=99
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SEE ALSO

113        r.compress, r.support, r.quant
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AUTHOR

116       U.S.Army Construction Engineering Research Laboratory
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SOURCE CODE

119       Available at: r.null source code (history)
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121       Main index | Raster index | Topics index | Keywords index  |  Graphical
122       index | Full index
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124       © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
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128GRASS 7.8.5                                                          r.null(1)
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