Provided by: grass-doc_7.8.2-1build3_all bug


       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.


       raster, algebra, statistics, aggregation, neighbor, focal statistics, filter


       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]

           Do not align output with the input

           Use circular neighborhood

           Allow output files to overwrite existing files

           Print usage summary

           Verbose module output

           Quiet module output

           Force launching GUI dialog

       input=name [required]
           Name of input raster map

           Name of an input raster map to select the cells which should be processed

       output=name[,name,...] [required]
           Name for output raster map

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

           Neighborhood size
           Default: 3

           Title for output raster map

           Text file containing weights

           Sigma (in cells) for Gaussian filter

           Quantile to calculate for method=quantile
           Options: 0.0-1.0


       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

       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 1
       selection 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 1
       Without 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:

           The average value within the neighborhood.  In the following example, the result would
           (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 |          |   |   |   |
              +---+---+---+          +---+---+---+

           The  value  found half-way through a list of the neighborhood’s values, when these are
           ranged in numerical order.

           The most frequently occurring value in the neighborhood.

           The minimum value within the neighborhood.

           The maximum value within the neighborhood.

           The range value within the neighborhood.

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

           The sum of values within the neighborhood.

           The count of filled (not NULL) cells.

           The  statistical  variance  of  values within the neighborhood (rounded to the nearest

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

           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

           The result will be the 90th percentile of neighborhood.

           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 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:
       To  calculate  an  annulus shaped neighborhood the contents of weight.txt file may be e.g.
       for size=5:
        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
       The way that weights are used depends upon the specific  aggregate  (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:
         sum(w[i]*x[i]) / sum(w[i])
       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.

           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.

           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 . . . . .


       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

       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.


   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)"




       Original version: Michael Shapiro, U.S.Army Construction Engineering Research Laboratory
       Updates for GRASS GIS 7 by Glynn Clements and others


       Available at: r.neighbors source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual