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

NAME

       r.mfilter  - Performs raster map matrix filter.

KEYWORDS

       raster, map algebra

SYNOPSIS

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

   Flags:
       -q
           Quiet

       -z
           Apply filter only to zero data values

       --overwrite
           Allow output files to overwrite existing files

       --verbose
           Verbose module output

       --quiet
           Quiet module output

   Parameters:
       input=name
           Name of input raster map

       output=name
           Name for output raster map

       filter=name
           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 zero category values in the input raster
       map layer.  The non-zero 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 zero 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 integers
.
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 integers. The integers 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-zero 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, rounding to the nearest integer.  (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-zero.)

       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

       For a floating point version of this command, see r.mfilter.fp.

       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

       Michael Shapiro, U.S.Army Construction Engineering Research Laboratory

       Last changed: $Date: 2011-11-08 03:29:50 -0800 (Tue, 08 Nov 2011) $

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