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

6       r.reclass  - Reclassify raster map based on category values.
7       Creates a new raster map whose category values are based upon a reclas‐
8       sification of the categories in an existing raster map.
9

KEYWORDS

11       raster, reclassification
12

SYNOPSIS

14       r.reclass
15       r.reclass --help
16       r.reclass input=name output=name rules=name  [title=string]    [--over‐
17       write]  [--help]  [--verbose]  [--quiet]  [--ui]
18
19   Flags:
20       --overwrite
21           Allow output files to overwrite existing files
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23       --help
24           Print usage summary
25
26       --verbose
27           Verbose module output
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29       --quiet
30           Quiet module output
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32       --ui
33           Force launching GUI dialog
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35   Parameters:
36       input=name [required]
37           Name of raster map to be reclassified
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39       output=name [required]
40           Name for output raster map
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42       rules=name [required]
43           File containing reclass rules
44           ’-’ for standard input
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46       title=string
47           Title for output raster map
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DESCRIPTION

50       r.reclass  creates an output map layer based on an input integer raster
51       map layer.  The output map layer will be a reclassification of the  in‐
52       put  map  layer  based  on reclass rules input to r.reclass, and can be
53       treated in much the same way that raster maps are treated.  A TITLE for
54       the output map layer may be (optionally) specified by the user.
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56       The  reclass  rules  are  read from standard input (i.e., from the key‐
57       board, redirected from a file, or piped through another program).
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59       Before using r.reclass the user must know the following:
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61       1      The new categories desired;  and, which old categories fit  into
62              which new categories.
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64       2      The names of the new categories.
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NOTES

67       In  fact,  the  r.reclass  program does not generate any new raster map
68       layers (in the interests of disk space conservation).  Instead,  a  re‐
69       class  table  is  stored  which will be used to reclassify the original
70       raster map layer each time the new (reclassed) map name  is  requested.
71       As  far  as the user (and programmer) is concerned, that raster map has
72       been created.
73
74       r.reclass only works on an integer input raster map; if the  input  map
75       is  instead  floating  point  data, you must multiply the input data by
76       some factor to achieve whole number  input  data,  otherwise  r.reclass
77       will round the raster values down to the next integer.
78
79       Also  note that although the user can generate a r.reclass map which is
80       based on another r.reclass map, the new r.reclass map will be stored in
81       GRASS  as  a  reclass of the original raster map on which the first re‐
82       classed map was based.  Therefore, while GRASS allows the user to  pro‐
83       vide  r.reclass  map layer information which is based on an already re‐
84       classified map (for the user’s convenience),  no  r.reclass  map  layer
85       (i.e.,  reclass  table)  will  ever be stored as a r.reclass of a r.re‐
86       class.
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88       To convert a reclass map to a regular raster map layer, set  your  geo‐
89       graphic region settings to match the settings in the header for the re‐
90       class map (with "g.region raster=reclass_map", or viewable by  running
91       r.info) and then run r.resample.
92
93       r.mapcalc  can be used to convert a reclass map to a regular raster map
94       layer as well:
95         r.mapcalc "raster_map = reclass_map"
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97       where raster_map is the name to be given to the new raster map, and re‐
98       class_map is an existing reclass map.
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100       Because  r.reclass  generates  internally simply a table by referencing
101       some original raster map layer rather than  creating  a  full  new  re‐
102       classed  raster  map layer, a r.reclass map layer will no longer be ac‐
103       cessible if the original raster map layer, upon which it was based,  is
104       later  removed. Therefore, attempting to remove a raster map layer from
105       which a r.reclass has been derived is only possible if the original map
106       is  removed  first.   Alternatively, a r.reclass map can be removed in‐
107       cluding its base map by using
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109       g.remove’s -b flag.
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111       A r.reclass map is not a true raster map layer.  Rather, it is a  table
112       of  reclassification values which reference the input raster map layer.
113       Therefore, users who wish to retain reclassified map layers  must  also
114       save  the  original input raster map layers from which they were gener‐
115       ated. Alternatively r.recode can be used.
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117       Category values which are not explicitly reclassified to a new value by
118       the user will be reclassified to NULL.
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120   Reclass Rules
121       Each line of input must have the following format:
122       input_categories=output_category  [label]
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124       where  each  line  of  input specifies the category values in the input
125       raster map layer to be reclassified to the new output_category category
126       value.   Specification  of a label to be associated with the new output
127       map layer category is optional.  If specified, it is  recorded  as  the
128       category  label  for  the  new category value.  The equal sign = is re‐
129       quired.  The input_category(ies) may consist of single category  values
130       or  a  range  of  such  values  in the format "low thru high." The word
131       "thru" must be present.
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133       To include all (remaining) values the asterix "*"  can  be  used.  This
134       rule  has  to  be set as last rule. No further rules are accepted after
135       setting this rule. The special rule "* = *" specifies  that  all  cate‐
136       gories  not  expicitly  set  by one of the above rules should be passed
137       through unaltered instead of being set to NULL.
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139       Categories to become no data are specified by setting the output  cate‐
140       gory value to "NULL".
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142       A line containing only the word end terminates the input.
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EXAMPLES

145   Reclass rules examples
146       The following examples may help clarify the reclass rules.
147
148       The  first  example  reclassifies  categories  1,  2 and 3 in the input
149       raster map layer "roads" to category 1 with category label "good  qual‐
150       ity"  in  the output map layer, and reclassifies input raster map layer
151       categories 4 and 5 to category 2 with the label "poor quality"  in  the
152       output map layer.
153           1 2 3   = 1    good quality
154           4 5     = 2    poor quality
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156       The  following  example reclassifies categories 1, 3 and 5 in the input
157       raster map layer to category 1 with category label  "poor  quality"  in
158       the  output  map  layer,  and reclassifies input raster map layer cate‐
159       gories 2, 4, and 6 to category 2 with the label "good quality"  in  the
160       output map layer.  All other values are reclassified to NULL.
161           1 3 5   = 1    poor quality
162           2 4 6   = 2    good quality
163           *       = NULL
164
165       The  following example reclassifies input raster map layer categories 1
166       thru 10 to output map layer category 1, input map layer  categories  11
167       thru  20 to output map layer category 2, and input map layer categories
168       21 thru 30 to output map layer category  3,  all  without  labels.  The
169       range from 30 to 40 is reclassified as NULL.
170            1 thru 10 = 1
171           11 thru 20 = 2
172           21 thru 30 = 3
173           30 thru 40  = NULL
174
175       The  following  example shows overlapping rules. Subsequent rules over‐
176       ride previous rules. Therefore, the below  example  reclassifies  input
177       raster  map layer categories 1 thru 19 and 51 thru 100 to category 1 in
178       the output map layer, input raster map layer categories 20 thru 24  and
179       26  thru  50  to  the output map layer category 2, and input raster map
180       layer category 25 to the output category 3.
181            1 thru 100     = 1    poor quality
182           20 thru 50 = 2    medium quality
183           25            = 3    good quality
184
185       The previous example could also have been entered as:
186            1 thru 19  51 thru 100   = 1    poor quality
187           20 thru 24  26 thru 50    = 2    medium quality
188           25                   = 3    good quality
189       or as:
190            1 thru 19  = 1    poor quality
191           51 thru 100      = 1
192           20 thru 24  = 2
193           26 thru 50  = 2    medium quality
194           25          = 3    good quality
195
196       The final example was given to show how the labels are handled.   If  a
197       new  category  value appears in more than one rule (as is the case with
198       new category values 1 and 2), the last label which  was  specified  be‐
199       comes  the  label  for  that category.  In this case the labels are as‐
200       signed exactly as in the two previous examples.
201
202   Usage example
203       In this example, the 21 classes of the landuse map (North Carolina sam‐
204       ple dataset) are simplified to 7 classes:
205       r.category landuse96_28m
206       0    not classified
207       1    High Intensity Developed
208       2    Low Intensity Developed
209       3    Cultivated
210       [...]
211       20   Water Bodies
212       21      Unconsolidated Sediment
213       # use this command or save rules with editor in textfile "landuserecl.txt"
214       echo "0 = NULL
215       1 2     = 1 developed
216       3       = 2 agriculture
217       4 6     = 3 herbaceous
218       7 8 9   = 4 shrubland
219       10 thru 18 = 5 forest
220       20      = 6 water
221       21      = 7 sediment" > landuserecl.txt
222       r.reclass input=landuse96_28m output=landclass96_recl \
223         rules=landuserecl.txt \
224         title="Simplified landuse classes 1996"
225       # verify result
226       r.category landuse96_recl
227       1    developed
228       2    agriculture
229       3    herbaceous
230       4    shrubland
231       5    forest
232       6    water
233       7    sediment
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SEE ALSO

236        r.recode, r.resample, r.rescale
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AUTHORS

239       James Westervelt,
240       Michael Shapiro
241       U.S.Army Construction Engineering Research Laboratory
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SOURCE CODE

244       Available at: r.reclass source code (history)
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246       Accessed: Mon Jun 20 16:46:22 2022
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248       Main  index  | Raster index | Topics index | Keywords index | Graphical
249       index | Full index
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251       © 2003-2022 GRASS Development Team, GRASS GIS 8.2.0 Reference Manual
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255GRASS 8.2.0                                                       r.reclass(1)
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