r.reclass(1grass) GRASS GIS User's Manual r.reclass(1grass)
NAME
r.reclass - Reclassify raster map based on category values.
Creates a new raster map whose category values are based upon a reclas-
sification of the categories in an existing raster map.
KEYWORDS
raster, reclassification
SYNOPSIS
r.reclass
r.reclass --help
r.reclass input=name output=name rules=name [title=string] [--over-
write] [--help] [--verbose] [--quiet] [--ui]
Flags:
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
input=name [required]
Name of raster map to be reclassified
output=name [required]
Name for output raster map
rules=name [required]
File containing reclass rules
’-’ for standard input
title=string
Title for output raster map
DESCRIPTION
r.reclass creates an output map layer based on an input integer raster
map layer. The output map layer will be a reclassification of the in-
put map layer based on reclass rules input to r.reclass, and can be
treated in much the same way that raster maps are treated. A TITLE for
the output map layer may be (optionally) specified by the user.
The reclass rules are read from standard input (i.e., from the key-
board, redirected from a file, or piped through another program).
Before using r.reclass the user must know the following:
1 The new categories desired; and, which old categories fit into
which new categories.
2 The names of the new categories.
NOTES
In fact, the r.reclass program does not generate any new raster map
layers (in the interests of disk space conservation). Instead, a re-
class table is stored which will be used to reclassify the original
raster map layer each time the new (reclassed) map name is requested.
As far as the user (and programmer) is concerned, that raster map has
been created.
r.reclass only works on an integer input raster map; if the input map
is instead floating point data, you must multiply the input data by
some factor to achieve whole number input data, otherwise r.reclass
will round the raster values down to the next integer.
Also note that although the user can generate a r.reclass map which is
based on another r.reclass map, the new r.reclass map will be stored in
GRASS as a reclass of the original raster map on which the first re-
classed map was based. Therefore, while GRASS allows the user to pro-
vide r.reclass map layer information which is based on an already re-
classified map (for the user’s convenience), no r.reclass map layer
(i.e., reclass table) will ever be stored as a r.reclass of a r.re-
class.
To convert a reclass map to a regular raster map layer, set your geo-
graphic region settings to match the settings in the header for the re-
class map (with "g.region raster=reclass_map", or viewable by running
r.info) and then run r.resample.
r.mapcalc can be used to convert a reclass map to a regular raster map
layer as well:
r.mapcalc "raster_map = reclass_map"
where raster_map is the name to be given to the new raster map, and re-
class_map is an existing reclass map.
Because r.reclass generates internally simply a table by referencing
some original raster map layer rather than creating a full new re-
classed raster map layer, a r.reclass map layer will no longer be ac-
cessible if the original raster map layer, upon which it was based, is
later removed. Therefore, attempting to remove a raster map layer from
which a r.reclass has been derived is only possible if the original map
is removed first. Alternatively, a r.reclass map can be removed in-
cluding its base map by using
g.remove’s -b flag.
A r.reclass map is not a true raster map layer. Rather, it is a table
of reclassification values which reference the input raster map layer.
Therefore, users who wish to retain reclassified map layers must also
save the original input raster map layers from which they were gener-
ated. Alternatively r.recode can be used.
Category values which are not explicitly reclassified to a new value by
the user will be reclassified to NULL.
Reclass Rules
Each line of input must have the following format:
input_categories=output_category [label]
where each line of input specifies the category values in the input
raster map layer to be reclassified to the new output_category category
value. Specification of a label to be associated with the new output
map layer category is optional. If specified, it is recorded as the
category label for the new category value. The equal sign = is re-
quired. The input_category(ies) may consist of single category values
or a range of such values in the format "low thru high." The word
"thru" must be present.
To include all (remaining) values the asterix "*" can be used. This
rule has to be set as last rule. No further rules are accepted after
setting this rule. The special rule "* = *" specifies that all cate-
gories not expicitly set by one of the above rules should be passed
through unaltered instead of being set to NULL.
Categories to become no data are specified by setting the output cate-
gory value to "NULL".
A line containing only the word end terminates the input.
EXAMPLES
Reclass rules examples
The following examples may help clarify the reclass rules.
The first example reclassifies categories 1, 2 and 3 in the input
raster map layer "roads" to category 1 with category label "good qual-
ity" in the output map layer, and reclassifies input raster map layer
categories 4 and 5 to category 2 with the label "poor quality" in the
output map layer.
1 2 3 = 1 good quality
4 5 = 2 poor quality
The following example reclassifies categories 1, 3 and 5 in the input
raster map layer to category 1 with category label "poor quality" in
the output map layer, and reclassifies input raster map layer cate-
gories 2, 4, and 6 to category 2 with the label "good quality" in the
output map layer. All other values are reclassified to NULL.
1 3 5 = 1 poor quality
2 4 6 = 2 good quality
* = NULL
The following example reclassifies input raster map layer categories 1
thru 10 to output map layer category 1, input map layer categories 11
thru 20 to output map layer category 2, and input map layer categories
21 thru 30 to output map layer category 3, all without labels. The
range from 30 to 40 is reclassified as NULL.
1 thru 10 = 1
11 thru 20 = 2
21 thru 30 = 3
30 thru 40 = NULL
The following example shows overlapping rules. Subsequent rules over-
ride previous rules. Therefore, the below example reclassifies input
raster map layer categories 1 thru 19 and 51 thru 100 to category 1 in
the output map layer, input raster map layer categories 20 thru 24 and
26 thru 50 to the output map layer category 2, and input raster map
layer category 25 to the output category 3.
1 thru 100 = 1 poor quality
20 thru 50 = 2 medium quality
25 = 3 good quality
The previous example could also have been entered as:
1 thru 19 51 thru 100 = 1 poor quality
20 thru 24 26 thru 50 = 2 medium quality
25 = 3 good quality
or as:
1 thru 19 = 1 poor quality
51 thru 100 = 1
20 thru 24 = 2
26 thru 50 = 2 medium quality
25 = 3 good quality
The final example was given to show how the labels are handled. If a
new category value appears in more than one rule (as is the case with
new category values 1 and 2), the last label which was specified be-
comes the label for that category. In this case the labels are as-
signed exactly as in the two previous examples.
Usage example
In this example, the 21 classes of the landuse map (North Carolina sam-
ple dataset) are simplified to 7 classes:
r.category landuse96_28m
0 not classified
1 High Intensity Developed
2 Low Intensity Developed
3 Cultivated
[...]
20 Water Bodies
21 Unconsolidated Sediment
# use this command or save rules with editor in textfile "landuserecl.txt"
echo "0 = NULL
1 2 = 1 developed
3 = 2 agriculture
4 6 = 3 herbaceous
7 8 9 = 4 shrubland
10 thru 18 = 5 forest
20 = 6 water
21 = 7 sediment" > landuserecl.txt
r.reclass input=landuse96_28m output=landclass96_recl \
rules=landuserecl.txt \
title="Simplified landuse classes 1996"
# verify result
r.category landuse96_recl
1 developed
2 agriculture
3 herbaceous
4 shrubland
5 forest
6 water
7 sediment
SEE ALSO
r.recode, r.resample, r.rescale
AUTHORS
James Westervelt,
Michael Shapiro
U.S.Army Construction Engineering Research Laboratory
SOURCE CODE
Available at: r.reclass source code (history)
Accessed: unknown
Main index | Raster index | Topics index | Keywords index | Graphical
index | Full index
© 2003-2022 GRASS Development Team, GRASS GIS 7.8.7 Reference Manual
GRASS 7.8.7 r.reclass(1grass)
Generated by dwww version 1.14 on Sun Dec 29 18:57:09 CET 2024.