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

SOURCE CODE

       Available at: r.grow source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual