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

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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GRASS 6.4.3                                                                                    r.reclass(1grass)