Provided by: grass-doc_6.4.3-3_all 
NAME
r.neighbors - Makes each cell category value a function of the category values assigned
to the cells around it, and stores new cell values in an output raster map layer.
KEYWORDS
raster, statistics
SYNOPSIS
r.neighbors
r.neighbors help
r.neighbors [-aqc] input=name output=name [method=string] [size=integer]
[title="phrase"] [weight=string] [gauss=float] [--overwrite] [--verbose] [--quiet]
Flags:
-a
Do not align output with the input
-q
Run quietly
-c
Use circular neighborhood
--overwrite
Allow output files to overwrite existing files
--verbose
Verbose module output
--quiet
Quiet module output
Parameters:
input=name
Name of input raster map
output=name
Name for output raster map
method=string
Neighborhood operation
Options:
average,median,mode,minimum,maximum,range,stddev,sum,variance,diversity,interspersion
Default: average
size=integer
Neighborhood size
Default: 3
title=
Title of the output raster map
weight=string
File containing weights
gauss=float
Sigma (in cells) for Gaussian filter
DESCRIPTION
r.neighbors looks at each cell in a raster input file, and examines the values assigned to
the cells in some user-defined "neighborhood" around it. It outputs a new raster map
layer in which each cell is assigned a value that is some (user-specified) function of the
values in that cell's neighborhood. For example, each cell in the output layer might be
assigned a value equal to the average of the values appearing in its 3 x 3 cell
"neighborhood" in the input layer.
The program will be run non-interactively if the user specifies program arguments (see
OPTIONS) on the command line. Alternately, the user can simply type r.neighbors on the
command line, without program arguments. In this case, the user will be prompted for flag
settings and parameter values.
OPTIONS
The user must specify the names of the raster map layers to be used for input and output,
the method used to analyze neighborhood values (i.e., the neighborhood function or
operation to be performed), and the size of the neighborhood. Optionally, the user can
also specify the TITLE to be assigned to the raster map layer output, elect to not align
the resolution of the output with that of the input (the -a option), run r.neighbors with
a custom matrix weights with the weight option, and elect to run r.neighbors quietly (the
-q option). These options are described further below.
Neighborhood Operation Methods: The neighborhood operators determine what new value a
center cell in a neighborhood will have after examining values inside its neighboring
cells. Each cell in a raster map layer becomes the center cell of a neighborhood as the
neighborhood window moves from cell to cell throughout the map layer. r.neighbors can
perform the following operations:
average
The average value within the neighborhood. In the following example, the result
would be:
(7*4 + 6 + 5 + 4*3)/9 = 5.66
The result is rounded to the nearest integer (in this case 6).
median
The value found half-way through a list of the neighborhood's values, when these
are ranged in numerical order.
mode
The most frequently occurring value in the neighborhood.
minimum
The minimum value within the neighborhood.
maximum
The maximum value within the neighborhood.
Raw Data Operation New Data
---------------- ----------------
| 7 | 7 | 5 | | | | |
|----|----|----| average |----|----|----|
| | 6 | |
|----|----|----| |----|----|----|
| 7 | 6 | 4 | | | | |
|----|----|----| |----|----|----|
range
The range value within the neighborhood.
stddev
The statistical standard deviation of values within the neighborhood (rounded to
the nearest integer).
sum
The sum of values within the neighborhood.
variance
The statistical variance of values within the neighborhood (rounded to the nearest
integer).
diversity
The number of different values within the neighborhood. In the above example, the
diversity is 4.
interspersion
The percentage of cells containing values which differ from the values assigned to
the center cell in the neighborhood, plus 1. In the above example, the
interspersion is:
5/8 * 100 + 1 = 63.5
The result is rounded to the nearest integer (in this case 64).
Neighborhood Size:
The neighborhood size specifies which cells surrounding any given cell fall into the
neighborhood for that cell. The size must be an odd integer. For example,
_ _ _
|_|_|_|
|_|_|_|
|_|_|_|
Matrix weights:
A custom matrix can be used if none of the neighborhood operation methods are desirable by
using the weight. This option must be used in conjunction with the size option to specify
the matrix size. The weights desired are to be entered into a text file. For example, to
calculate the focal mean with a matrix size of 3,
r.neigbors in=input.map out=output.map size=3 weight=weights.txt
The contents of the weight.txt file:
3 3 3
1 4 8
9 5 3
This corresponds to the following 3x3 matrix:
-------
|3|3|3|
-------
|1|4|8|
-------
|9|5|3|
-------
FLAGS
-a
If specified, r.neighbors will not align the output raster map layer with that of
the input raster map layer. The r.neighbors program works in the current
geographic region. It is recommended, but not required, that the resolution of the
geographic region be the same as that of the raster map layer. By default, if
unspecified, r.neighbors will align these geographic region settings.
-c This flag will use a circular neighborhood for the moving analysis window, centered
on the current cell.
The exact masks for the first few neighborhood sizes are as follows:
3x3 . X . 5x5 . . X . . 7x7 . . . X . . .
X O X . X X X . . X X X X X .
. X . X X O X X . X X X X X .
. X X X . X X X O X X X
. . X . . . X X X X X .
. X X X X X .
. . . X . . .
9x9 . . . . X . . . . 11x11 . . . . . X . . . . .
. . X X X X X . . . . X X X X X X X . .
. X X X X X X X . . X X X X X X X X X .
. X X X X X X X . . X X X X X X X X X .
X X X X O X X X X . X X X X X X X X X .
. X X X X X X X . X X X X X O X X X X X
. X X X X X X X . . X X X X X X X X X .
. . X X X X X . . . X X X X X X X X X .
. . . . X . . . . . X X X X X X X X X .
. . X X X X X X X . .
. . . . . X . . . . .
-q
If specified, r.neighbors will run relatively quietly (i.e., without printing to
standard output notes on the program's progress). If unspecified, the program will
print messages to standard output by default.
NOTES
The r.neighbors program works in the current geographic region with the current mask, if
any. It is recommended, but not required, that the resolution of the geographic region be
the same as that of the raster map layer. By default, r.neighbors will align these
geographic region settings. However, the user can elect to keep original input and output
resolutions which are not aligned by specifying this (e.g., using the -a option).
r.neighbors doesn't propagate NULLs, but computes the aggregate over the non-NULL cells in
the neighborhood.
The -c flag and the weights parameter are mutually exclusive. Any use of the two together
will produce an error. Differently-shaped neighborhood analysis windows may be achieved by
using the weight= parameter to specify a weights file where all values are equal. The user
can also vary the weights at the edge of the neighborhood according to the proportion of
the cell that lies inside the neighborhood circle, effectively anti-aliasing the analysis
mask.
For aggregates where a weighted calculation isn't meaningful (specifically: minimum,
maximum, diversity and interspersion), the weights are used to create a binary mask, where
zero causes the cell to be ignored and any non-zero value causes the cell to be used.
r.neighbors copies the GRASS color files associated with the input raster map layer for
those output map layers that are based on the neighborhood average, median, mode, minimum,
and maximum. Because standard deviation, variance, diversity, and interspersion are
indices, rather than direct correspondents to input values, no color files are copied for
these map layers. (The user should note that although the color file is copied for
average neighborhood function output, whether or not the color file makes sense for the
output will be dependent on the input data values.)
SEE ALSO
g.region
r.clump
r.mapcalc
r.mfilter
r.statistics
r.support
AUTHOR
Michael Shapiro, U.S.Army Construction Engineering Research Laboratory
Last changed: $Date: 2010-09-21 05:53:31 -0700 (Tue, 21 Sep 2010) $
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