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

Provided by: grass-doc_7.8.2-1build3_all

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)

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