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# r.grow

## man page of r.grow

### r.grow: Generates a raster map layer with contiguous areas grown by one cell.

```NAME
r.grow   -  Generates a raster map layer with contiguous areas grown by
one cell.

KEYWORDS
raster

SYNOPSIS
r.grow
r.grow help
r.grow [-q] input=name  output=name   [radius=float]    [metric=string]
[old=integer]   [new=integer]   [--overwrite]  [--verbose]  [--quiet]

Flags:
-q
Quiet

--overwrite
Allow output files to overwrite existing files

--verbose
Verbose module output

--quiet
Quiet module output

Parameters:
input=name
Name of input raster map

output=name
Name for output raster map

Radius of buffer in raster cells
Default: 1.01

metric=string
Metric
Options: euclidean,maximum,manhattan
Default: euclidean

old=integer
Value to write for input cells which are non-NULL (-1 => NULL)

new=integer
Value to write for "grown" cells

DESCRIPTION
r.grow  adds  cells  around  the  perimeters  of  all  areas in a user-
specified raster map layer and stores the output in a  new  raster  map
layer.  The  user  can  use it to grow by one or more than one cell (by
varying the size of the radius parameter), or like r.buffer,  but  with
the  option  of  preserving  the  original  cells (similar to combining
r.buffer and r.patch).

NOTES
The user has the option of specifying  three  different  metrics  which
control  the  geometry in which grown cells are created, (controlled by
the metric parameter): Euclidean, Manhattan, and Maximum.

The Euclidean distance or Euclidean metric 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: </div>
Cells grown using this metric would form isolines of distance that are
circular from a given point, with the distance given by the radius.

The Manhattan metric, or Taxicab geometry, is a form of geometry in
which the usual metric of Euclidean geometry is replaced by a new
metric  in  which  the  distance  between  two points is the sum of the
(absolute)
differences of their coordinates. The name alludes to the  grid  layout
of
most streets on the island of Manhattan, which causes the shortest path
a
car could take between two points in the city to have length  equal  to
the
points' distance in taxicab geometry.
The formula is given by:
</div>
where  cells  grown  using  this metric would form isolines of distance
that are
rhombus-shaped from a given point.

The Maximum metric is given by the formula
</div>
where the isolines of distance from a point are squares.

If there are two cells which are equal candidates to grow into an empty
space,
r.grow will choose the northernmost candidate; if there are multiple
candidates with the same northing, the westernmost is chosen.

EXAMPLE
You can shrink inwards by preparing an inverse map first, and then
inverting the resulting grown map. For example:

# Spearfish sample dataset
MAP=fields
g.region rast=\$MAP
r.mapcalc "inverse = if(isnull(\$MAP), 1, null())"
r.grow in=inverse out=inverse.grown
r.mapcalc "\$MAP.shrunken = if(isnull(inverse.grown), \$MAP, null())"
r.colors \$MAP.shrunken rast=\$MAP
g.remove inverse,inverse.grown

r.buffer,
r.grow.distance,
r.patch

Wikipedia Entry: Euclidean Metric
Wikipedia Entry: Manhattan Metric

AUTHORS
Marjorie Larson, U.S. Army Construction Engineering Research Laboratory

Glynn Clements

Last changed: \$Date: 2010-03-30 01:24:01 +0200 (Tue, 30 Mar 2010) \$

Full index

(C) 2003-2010 GRASS Development Team

R.GROW(1)
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