.TH r.median 1grass "" "GRASS 6.4.2" "Grass User's Manual"
.SH NAME
\fI\fBr.median\fR\fR  - Finds the median of values in a cover map within areas assigned the same category value in a user-specified base map.
.SH KEYWORDS
raster, statistics
.SH SYNOPSIS
\fBr.median\fR
.br
\fBr.median help\fR
.br
\fBr.median base\fR=\fIname\fR \fBcover\fR=\fIname\fR \fBoutput\fR=\fIname\fR  [--\fBoverwrite\fR]  [--\fBverbose\fR]  [--\fBquiet\fR] 
.SS Flags:
.IP "\fB--overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB--verbose\fR" 4m
.br
Verbose module output
.IP "\fB--quiet\fR" 4m
.br
Quiet module output
.PP
.SS Parameters:
.IP "\fBbase\fR=\fIname\fR" 4m
.br
Name of base raster map
.IP "\fBcover\fR=\fIname\fR" 4m
.br
Name of cover raster map
.IP "\fBoutput\fR=\fIname\fR" 4m
.br
Name for output raster map
.PP
.SH DESCRIPTION
\fIr.median\fR calculates the median category of data
contained in a \fBcover\fR raster map layer for areas
assigned the same category value in the user-specified
\fBbase\fR raster map layer.  These median values are
stored in the new \fBoutput\fR map layer.
.PP
The \fBoutput\fR map is actually a \fIreclass\fR of the \fBbase\fR map.
The \fBbase\fR  map is an existing raster map layer in the user's current
mapset search path.  For each group of cells assigned the
same category value in the \fBbase\fR map, the median of
the values assigned these cells in the \fBcover\fR map
will be computed.
.PP
The \fBcover\fR map is an existing raster map layer containing the values
to be used to compute the median within each category of the \fBbase\fR map.
.SH NOTES
The user should use the results of \fIr.median\fR with
care.  Since this utility assigns a value to each cell
which is based on global information (i.e., information at
spatial locations other than just the location of the cell
itself), the resultant map layer is only valid if the
geographic region and mask settings are the same as they
were at the time that the result map was created.
.PP
Results are affected by the current region settings and mask.
.SH EXAMPLE
Median K-factor (erosion) for Spearfish fields:
\fC
.DS
.br
g.region rast=fields -p
.br
r.median base=fields cover=soils.Kfactor output=K.by.farm.median
.br
r.univar K.by.farm.median
.br
.DE
\fR
.SH SEE ALSO
\fIg.region\fR,
\fIr.average\fR,
\fIr.category\fR,
\fIr.clump\fR,
\fIr.describe\fR,
\fIr.mapcalc\fR,
\fIr.mfilter\fR,
\fIr.mode\fR,
\fIr.neighbors\fR,
\fIr.reclass\fR,
\fIr.statistics\fR,
\fIr.stats\fR,
\fIr.univar\fR
.SH AUTHOR
Michael Shapiro,
U.S.Army Construction Engineering Research Laboratory
.PP
\fILast changed: $Date: 2008-05-16 21:09:06 +0200 (Fri, 16 May 2008) $\fR
.PP
Full index
.PP
© 2003-2011 GRASS Development Team