.TH r.grow.distance 1grass "" "GRASS 6.4.2" "Grass User's Manual"
.SH NAME
\fI\fBr.grow.distance\fR\fR  - Generates a raster map layer of distance to features in input layer.
.SH KEYWORDS
raster, geometry
.SH SYNOPSIS
\fBr.grow.distance\fR
.br
\fBr.grow.distance help\fR
.br
\fBr.grow.distance input\fR=\fIname\fR  [\fBdistance\fR=\fIname\fR]   [\fBvalue\fR=\fIname\fR]   [\fBmetric\fR=\fIstring\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 "\fBinput\fR=\fIname\fR" 4m
.br
Name of input raster map
.IP "\fBdistance\fR=\fIname\fR" 4m
.br
Name for distance output map
.IP "\fBvalue\fR=\fIname\fR" 4m
.br
Name for value output map
.IP "\fBmetric\fR=\fIstring\fR" 4m
.br
Metric
.br
Options: \fIeuclidean,squared,maximum,manhattan\fR
.br
Default: \fIeuclidean\fR
.PP
.SH DESCRIPTION
\fIr.grow.distance\fR generates raster maps representing the
distance to the nearest non-null cell in the input map and/or the
value of the nearest non-null cell.
.SH NOTES
The user has the option of specifying four different metrics which
control the geometry in which grown cells are created, (controlled by
the \fBmetric\fR parameter): \fIEuclidean\fR, \fISquared\fR,
\fIManhattan\fR, and \fIMaximum\fR.
.PP
The \fIEuclidean distance\fR or \fIEuclidean metric\fR is the "ordinary" distance 
between two points that one would measure with a ruler, which can be 
proven by repeated application of the Pythagorean theorem. 
The formula is given by: 
\fC
.DSd(dx,dy) = sqrt(dx^2 + dy^2)
.DE
\fR</div>
.br
.br
Cells grown using this metric would form isolines of distance that are
.br
circular from a given point, with the distance given by the \fBradius\fR.
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.br
.PP
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The \fISquared\fR metric is the \fIEuclidean\fR distance squared,
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i.e. it simply omits the square-root calculation. This may be faster,
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and is sufficient if only relative values are required.
.br
.br
.PP
.br
.br
The \fIManhattan metric\fR, or \fITaxicab geometry\fR, is a form of geometry in 
.br
which the usual metric of Euclidean geometry is replaced by a new 
.br
metric in which the distance between two points is the sum of the (absolute) 
.br
differences of their coordinates. The name alludes to the grid layout of 
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most streets on the island of Manhattan, which causes the shortest path a 
.br
car could take between two points in the city to have length equal to the
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points' distance in taxicab geometry.
.br
The formula is given by:
.br
.br
\fC
.DSd(dx,dy) = abs(dx) + abs(dy)
.DE
\fR</div>
.br
.br
where cells grown using this metric would form isolines of distance that are
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rhombus-shaped from a given point. 
.br
.br
.PP
.br
.br
The \fIMaximum metric\fR is given by the formula
.br
.br
\fC
.DSd(dx,dy) = max(abs(dx),abs(dy))
.DE
\fR</div>
.br
.br
where the isolines of distance from a point are squares.
.br
.br
.br
.SH EXAMPLE
.br
.br
Spearfish sample dataset
.br
\fC
.DS
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r.grow.distance input=roads distance=dist_from_roads
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.DE
\fR
.SH SEE ALSO
\fI
r.grow
.br
r.buffer
.br
r.cost
.br
r.patch
\fR
.PP
\fI
Wikipedia Entry:
Euclidean Metric
.br
Wikipedia Entry:
Manhattan Metric
\fR
.SH AUTHORS
Glynn Clements
.PP
\fILast changed: $Date: 2008-11-20 11:59:22 +0100 (Thu, 20 Nov 2008) $\fR
.PP
Full index
.PP
© 2003-2011 GRASS Development Team