Ubuntu Manpage: r.reclass - Creates a new map layer whose category values are based upon a

NAME

       r.reclass    -   Creates  a  new  map  layer  whose  category  values  are  based  upon  a
       reclassification of the categories in an existing raster map layer.

KEYWORDS

       raster, statistics, reclass

SYNOPSIS

       r.reclass
       r.reclass help
       r.reclass   input=name   output=name    [rules=name]     [title=string]      [--overwrite]
       [--verbose]  [--quiet]

   Flags:
       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=name
           Raster map to be reclassified

       output=name
           Name for output raster map

       rules=name
           File containing reclass rules

       title=string
           Title for the resulting 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 input 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 keyboard, 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 reclass 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 acheive 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 map will be stored in GRASS as a reclass of the
original raster map on which the first reclassed map was based. Therefore, while GRASS
allows the user to provide r.reclass map layer information which is based on an already
reclassified 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.reclass.

To convert a reclass map to a regular raster map layer, set your geographic region
settings to match the settings in the header for the reclass map (with "g.region
rast=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 reclass_map is an
existing reclass map.

Because r.reclass generates a table referencing some original raster map layer rather than
creating a reclassed raster map layer, a r.reclass map layer will no longer be accessible
if the original raster map layer upon which it was based is later removed.

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 generated. 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 required.
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 categories 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 category value to "NULL".

A line containing only the word end terminates the input.

EXAMPLES

The following examples may help clarify the reclass rules.

1. This example reclassifies categories 1, 2 and 3 in the input raster map layer
"roads" to category 1 with category label "good quality" 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

2. This 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 categories 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

3. This 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

4. Subsequent rules override 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

5. 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 becomes the label for that category. In this case the labels
are assigned exactly as in the two previous examples.

AUTHORS

       James Westervelt,
       Michael Shapiro
       U.S.Army Construction Engineering Research Laboratory

       Last changed: $Date: 2009-09-19 08:10:59 -0700 (Sat, 19 Sep 2009) $

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