**-m**- Output distances in meters instead of map units
**-n**- Calculate distance to nearest NULL cell
**--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

**input**=*name***[required]**- Name of input raster map
**distance**=*name*- Name for distance output raster map
**value**=*name*- Name for value output raster map
**metric**=*string*- Metric
- Options:
*euclidean, squared, maximum, manhattan, geodesic* - Default:
*euclidean*

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

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)

The *Squared* metric is the *Euclidean* distance squared,
i.e. it simply omits the square-root calculation. This may be faster,
and is sufficient if only relative values are required.

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)

The *Maximum metric* is given by the formula

d(dx,dy) = max(abs(dx),abs(dy))

The *Geodesic metric* is calculated as geodesic distance, to
be used only in latitude-longitude locations. It is recommended
to use it along with the *-m* flag in order to output
distances in meters instead of map units.

g.region raster=streams_derived -p r.grow.distance input=streams_derived distance=dist_from_streams r.colors map=dist_from_streams color=rainbow

g.region raster=sea -p r.grow.distance -m input=sea distance=dist_from_sea_geodetic metric=geodesic r.colors map=dist_from_sea_geodetic color=rainbow

*
Wikipedia Entry:
Euclidean Metric
Wikipedia Entry:
Manhattan Metric
*

Available at: r.grow.distance source code (history)

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