## table of contents

r.neighbors(1grass) | GRASS GIS User's Manual | r.neighbors(1grass) |

# 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, algebra, statistics, aggregation, neighbor, focal statistics, filter

# SYNOPSIS¶

**r.neighbors**

**r.neighbors --help**

**r.neighbors** [-**ac**] **input**=*name*
[**selection**=*name*] **output**=*name*[,*name*,...]
[**method**=*string*[,*string*,...]]
[**size**=*integer*] [**title**=*phrase*]
[**weight**=*name*] [**gauss**=*float*]
[**quantile**=*float*[,*float*,...]] [--**overwrite**]
[--**help**] [--**verbose**] [--**quiet**] [--**ui**]

## Flags:¶

## Parameters:¶

**input**=*name***[required]**-

Name of input raster map **selection**=*name*-

Name of an input raster map to select the cells which should be processed **output**=*name[,**name*,...]**[required]**-

Name for output raster map **method**=*string[,**string*,...]-

Neighborhood operation

Options:*average, median, mode, minimum, maximum, range, stddev, sum, count, variance, diversity, interspersion, quart1, quart3, perc90, quantile*

Default:*average* **size**=*integer*-

Neighborhood size

Default:*3* **title**=*phrase*-

Title for output raster map **weight**=*name*-

Text file containing weights **gauss**=*float*-

Sigma (in cells) for Gaussian filter **quantile**=*float[,**float*,...]-

Quantile to calculate for method=quantile

Options:*0.0-1.0*

# 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. Note that the centre cell is also included in the calculation.

## 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.

The user can optionally specify a **selection** map, to compute
new values only where the raster cells of the selection map are not NULL. In
case of a NULL cells, the values from the input map are copied into the
output map. This may useful to smooth only parts of an elevation map (pits,
peaks, ...).

*Example how to use a selection map with method=average:*

input map:

1 1 1 1 1 1 1 1 1 1 1 1 10 1 1 1 1 1 1 1 1 1 1 1 1selection map, NULL values are marked as *:

* * * * * * * 1 * * * 1 1 1 * * * 1 * * * * * * *The output map:

1 1 1 1 1 1 1 2 1 1 1 2 2 2 1 1 1 2 1 1 1 1 1 1 1Without using the selection map, the output map would look like this:

1 1 1 1 1 1 2 2 2 1 1 2 2 2 1 1 2 2 2 1 1 1 1 1 1

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
run **r.neighbors** with a custom matrix weights with the
*weight* 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 = 5.6667

The result is rounded to the nearest integer (in this case 6).

Raw Data Operation New Data

+---+---+---+ +---+---+---+

| 7 | 7 | 5 | | | | |

+---+---+---+ average +---+---+---+

| 4 | 7 | 4 |--------->| | 6 | |

+---+---+---+ +---+---+---+

| 7 | 6 | 4 | | | | |

+---+---+---+ +---+---+---+ **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. **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. **count**-

The count of filled (not NULL) cells. **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). **quart1, quart3**-

The result will be the first or the third quartile (equal of 25th and 75th percentiles). **perc90**-

The result will be the 90th percentile of neighborhood. **quantile**-

Any quantile as specified by "quantile" input parameter.

*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 and represent the length of one
of moving window edges in cells. For example, a size value of 3 will result
in

_ _ _

|_|_|_|

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

|_|_|_|

*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.txtThe contents of the weight.txt file:

3 3 3 1 4 8 9 5 3This corresponds to the following 3x3 matrix:

+-+-+-+ |3|3|3| +-+-+-+ |1|4|8| +-+-+-+ |9|5|3| +-+-+-+To calculate an annulus shaped neighborhood the contents of weight.txt file may be e.g. for size=5:

The way that weights are used depends upon the specific aggregate (

0 1 1 1 0

1 0 0 0 1

1 0 0 0 1

1 0 0 0 1

0 1 1 1 0

**method**) being used. However, most of the aggregates have the property that multiplying all of the weights by the same factor won’t change the final result (an exception is

**method=count**). Also, most (if not all) of them have the properties that an integer weight of N is equivalent to N occurrences of the cell value, and having all weights equal to one produces the same result as when weights are not used. When weights are used, the calculation for

**method=average**is:

In the case where all weights are zero, this will end up with both the numerator and denominator to zero, which produces a NULL result.

sum(w[i]*x[i]) / sum(w[i])

## 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 . . . . .

# 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 select 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.)

## Propagation of output precision¶

The following logic has been implemented: For any aggregate, there are two factors affecting the output type:

**1**- Whether the input map is integer or floating-point.
**2**- Whether the weighted or unweighted version of the aggregate is used.

These combine to create four possibilities:

input type/weight | integer | float | ||||||

no | yes | no | yes | |||||

average | float | float | float | float | ||||

median | [1] | [1] | float | float | ||||

mode | integer | integer | [2] | [2] | ||||

minimum | integer | integer | float | float | ||||

maximum | integer | integer | float | float | ||||

range | integer | integer | float | float | ||||

stddev | float | float | float | float | ||||

sum | integer | float | float | float | ||||

count | integer | float | integer | float | ||||

variance | float | float | float | float | ||||

diversity | integer | integer | integer | integer | ||||

interspersion | integer | integer | integer | integer | ||||

quart1 | [1] | [1] | float | float | ||||

quart3 | [1] | [1] | float | float | ||||

perc90 | [1] | [1] | float | float | ||||

quantile | [1] | [1] | float | float |

[1] For integer input, quantiles may produce float results from
interpolating between adjacent values.

[2] Calculating the mode of floating-point data is essentially
meaningless.

With the current aggregates, there are 5 cases:

**1**- Output is always float: average, variance, stddev, quantiles (with interpolation).
**2**- Output is always integer: diversity, interspersion.
**3**- Output is integer if unweighted, float if weighted: count.
**4**- Output matches input: minimum, maximum, range, mode (subject to note 2 above), quantiles (without interpolation).
**5**- Output is integer for integer input and unweighted aggregate, otherwise float: sum.

# EXAMPLES¶

## Measure occupancy of neighborhood¶

Set up 10x10 computational region to aid visual inspection of
results

g.region rows=10 cols=10

Fill 50% of computational region with randomly located cells.
"distance=0" will allow filling adjacent cells.

r.random.cells output=random_cells distance=0 ncells=50

Count non-empty (not NULL) cells in 3x3 neighborhood

r.neighbors input=random_cells output=counts method=count

Optionally - exclude centre cell from the count (= only look
around)

r.mapcalc "cound_around = if( isnull(random_cells), counts, counts - 1)"

# SEE ALSO¶

*g.region*

*r.clump*

*r.mapcalc*

*r.mfilter*

*r.statistics*

*r.support*

# AUTHORS¶

Original version: Michael Shapiro, U.S.Army Construction
Engineering Research Laboratory

Updates for GRASS GIS 7 by Glynn Clements and others

# SOURCE CODE¶

Available at: r.neighbors source code (history)

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© 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual

GRASS 7.8.5 |