Ubuntu Manpage: r.mfilter - Performs raster map matrix filter.

NAME

       r.mfilter  - Performs raster map matrix filter.

KEYWORDS

       raster, algebra, statistics, filter

SYNOPSIS

       r.mfilter
       r.mfilter --help
       r.mfilter  [-z]  input=name  output=name  filter=name   [repeat=integer]    [title=string]
       [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -z
           Apply filter only to null data values

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       input=name [required]
           Name of input raster map

       output=name [required]
           Name for output raster map

       filter=name [required]
           Path to filter file

       repeat=integer
           Number of times to repeat the filter
           Default: 1

       title=string
           Output raster map title

DESCRIPTION

       r.mfilter filters the raster input to produce the raster output according  to  the  matrix
       filter  designed  by  the  user  (see  FILTERS below).  The filter is applied repeat times
       (default value is 1).  The output raster map layer can be given a TITLE if desired.  (This
       TITLE should be put in quotes if it contains more than one word.)  With -z flag the filter
       is applied only to null values in the input  raster  map  layer.   The  non-null  category
       values  are  not  changed.   Note that if there is more than one filter step, this rule is
       applied to the intermediate raster map layer -- only null  category  values  which  result
       from the first filter will be changed.  In most cases this will NOT be the desired result.
       Hence -z should be used only with single step filters.

       The filter parameter defines the name of an existing, user-created UNIX ASCII  file  whose
       contents is a matrix defining the way in which the input file will be filtered. The format
       of this file is described below, under FILTERS.

       The repeat parameter defines the number of times the filter is to be applied to the  input
       data.

FILTERS

The filter file is a normal UNIX ASCII file designed by the user. It has the following
format:
TITLE TITLE
MATRIX n
.
n lines of n values
.
DIVISOR d
TYPE S/P

TITLE
A one-line TITLE for the filter. If a TITLE was not specified on the command line, it
can be specified here. This TITLE would be used to construct a TITLE for the
resulting raster map layer. It should be a one-line description of the filter.

MATRIX
The matrix (n x n) follows on the next n lines. n must be an odd integer greater than
or equal to 3. The matrix itself consists of n rows of n values. The values must be
separated from each other by at least 1 blank.

DIVISOR
The filter divisor is d. If not specified, the default is 1. If the divisor is zero
(0), then the divisor is dependent on the category values in the neighborhood (see HOW
THE FILTER WORKS below).

TYPE
The filter type. S means sequential, while P mean parallel. If not specified, the
default is S.

Sequential filtering happens in place. As the filter is applied to the raster map layer,
the category values that were changed in neighboring cells affect the resulting category
value of the current cell being filtered.

Parallel filtering happens in such a way that the original raster map layer category
values are used to produce the new category value.

More than one filter may be specified in the filter file. The additional filter(s) are
described just like the first. For example, the following describes two filters:

EXAMPLE FILTER FILE

             TITLE     3x3 average, non-null data only, followed by 5x5 average
            MATRIX    3
            1 1 1
            1 1 1
            1 1 1
            DIVISOR   0
            TYPE      P
            MATRIX    5
            1 1 1 1 1
            1 1 1 1 1
            1 1 1 1 1
            1 1 1 1 1
            1 1 1 1 1
            DIVISOR   25
            TYPE      P

HOW THE FILTER WORKS

       The  filter  process  produces  a new category value for each cell in the input raster map
       layer by multiplying the category values of the cells in the n x n neighborhood around the
       center  cell  by the corresponding matrix value and adding them together.  If a divisor is
       specified, the sum is divided by this divisor.  (If a zero divisor was specified, then the
       divisor  is computed for each cell as the sum of the MATRIX values where the corresponding
       input cell is non-null.)

       If more than one filter step is specified, either because the  repeat  value  was  greater
       than  one  or  because  the  filter  file  contained more than one matrix, these steps are
       performed sequentially. This means that first one filter is applied to  the  entire  input
       raster map layer to produce an intermediate result; then the next filter is applied to the
       intermediate result to produce another intermediate result;  and so on,  until  the  final
       filter is applied.  Then the output cell is written.

NOTES

       If  the  resolution  of  the  geographic  region does not agree with the resolution of the
       raster map layer, unintended resampling of the original data may occur.  The  user  should
       be sure that the geographic region is set properly.

AUTHOR

       Glynn   Clements.   Based  upon  r.mfilter,  by  Michael  Shapiro,  U.S.Army  Construction
       Engineering Research Laboratory

SOURCE CODE

       Available at: r.mfilter source code (history)

       Accessed: unknown

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