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r.mfilter - Performs raster map matrix filter.
raster, map algebra
r.mfilter [-qz] input=name output=name filter=name [repeat=integer] [title=string] [--overwrite] [--verbose] [--quiet]
- Apply filter only to zero data values
- Allow output files to overwrite existing files
- Verbose module output
- Quiet module output
- Name of input raster map
- Name for output raster map
- Path to filter file
- Number of times to repeat the filter
- Default: 1
- Output raster map title
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.
The filter file is a normal UNIX ASCII file designed by the user.
It has the following format:
n lines of n integers
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.
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.
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).
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
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 1 1 1 1
1 1 1 1 1
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.
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.
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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