r.mfilter(1grass) GRASS GIS User's Manual r.mfilter(1grass)
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 accord-
ing 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 fil-
ter will be changed. In most cases this will NOT be the desired re-
sult. 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 in-
put 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 cate-
gory 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 addi-
tional 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 writ-
ten.
NOTES
If the resolution of the geographic region does not agree with the res-
olution 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.
SEE ALSO
g.region, r.clump, r.neighbors, r.resamp.filter
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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