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**NAME**

r.mfilter- Performs raster map matrix filter.

**KEYWORDS**

raster, map algebra

**SYNOPSIS**

r.mfilterr.mfilterhelpr.mfilter[-qz]input=nameoutput=namefilter=name[repeat=integer] [title=string] [--overwrite] [--verbose] [--quiet]Flags:-qQuiet-zApply filter only to zero data values--overwriteAllow output files to overwrite existing files--verboseVerbose module output--quietQuiet module outputParameters:input=nameName of input raster mapoutput=nameName for output raster mapfilter=namePath to filter filerepeat=integerNumber of times to repeat the filter Default:1title=stringOutput raster map title

**DESCRIPTION**

r.mfilterfilters the rasterinputto produce the rasteroutputaccording to the matrixfilterdesigned by the user (seeFILTERSbelow). The filter is appliedrepeattimes (defaultvalueis 1). Theoutputraster map layer can be given aTITLEif desired. (This TITLE should be put in quotes if it contains more than one word.) With-zflag 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. Thefilterparameter defines the name of an existing, user-created UNIX ASCII file whose contents is a matrix defining the way in which theinputfile will be filtered. The format of this file is described below, under FILTERS. Therepeatparameter defines the number of times thefilteris to be applied to theinputdata.

**FILTERS**

Thefilterfile 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.nmust 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 isd. 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.Smeans sequential, whilePmean 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, seer.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.

**SEE** **ALSO**

g.region,r.clump,r.mfilter.fp,r.neighbors

**AUTHOR**

Michael Shapiro, U.S.Army Construction Engineering Research LaboratoryLastchanged:$Date:2011-11-0803:29:50-0800(Tue,08Nov2011)$Full index © 2003-2013 GRASS Development Team