r.neighbors

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.
(GRASS Raster Program)

SYNOPSIS

r.neighbors
r.neighbors help
r.neighbors [-aq] input=name output=name method=name size=value [TITLE="phrase"]

DESCRIPTION

r.neighbors looks at each cell in a raster input file, and examines the category 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 category 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 category value equal to the average of the category 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 category 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), 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 category value a center cell in a neighborhood will have after examining category 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 category 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 category value found half-way through a list of the neighborhood's category values, when these are ranged in numerical order.

mode

The most frequently occurring category value in the neighborhood.

minimum

The minimum category value within the neighborhood.

maximum

The maximum category value within the neighborhood.

       Raw Data     Operation     New Data
   ----------------          ----------------
   | 7  | 7  |  5 |          |    |    |    |
   |----|----|----| average  |----|----|----|
   | 4  | 7  |  4 |--------->|    |  6 |    |
   |----|----|----|          |----|----|----|
   | 7  | 6  |  4 |          |    |    |    |
   |----|----|----|          |----|----|----|

stddev

The statistical standard deviation of category values within the neighborhood (rounded to the nearest integer).

variance

The statistical variance of category values within the neighborhood (rounded to the nearest integer).

diversity

The number of different category values within the neighborhood. In the above example, the diversity is 4.

interspersion

The percentage of cells containing categories which differ from the category 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). ERROR .RE

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. Options are: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, and 25. For example,

                              _ _ _
                             |_|_|_| 
    3 x 3 neighborhood --->  |_|_|_|
                             |_|_|_|

-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.

-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 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 category values, no color files are copied for these map layers. (The user should note that although the color file is copied for averaged neighborhood function output, whether or not the color file makes sense for the output will be dependent on the input data values.)

AUTHOR