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NAME

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

KEYWORDS

       raster, distance, proximity

SYNOPSIS

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

   Flags:
       -m
           Radius is in map units rather than cells

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       input=name [required]
           Name of input raster map

       output=name [required]
           Name for output raster map

       radius=float
           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).

       If radius is negative,r.grow shrinks areas by removing cells around the perimeters of  all
       areas.

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:
       d(dx,dy) = sqrt(dx^2 + dy^2)
       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:
       d(dx,dy) = abs(dx) + abs(dy)
       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
       d(dx,dy) = max(abs(dx),abs(dy))
       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

       In this example, the lakes map in the North Carolina sample dataset location is buffered:
       g.region raster=lakes -p
       # the lake raster map pixel resolution is 10m
       r.grow input=lakes output=lakes_grown_100m radius=10
       Shrinking instead of growing:
       g.region raster=lakes -p
       # the lake raster map pixel resolution is 10m
       r.grow input=lakes output=lakes_shrunk_100m radius=-10

SEE ALSO

        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: 2018-12-06 17:53:42 +0100 (Thu, 06 Dec 2018) $

SOURCE CODE

       Available at: r.grow source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.6.0 Reference Manual