r.grow(1)

NAME
r.grow

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

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: 2010-03-30 01:24:01 +0200 (Tue, 30 Mar 2010) $

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