r.grow.distance - GRASS GIS manual

NAME

r.grow.distance - Generates a raster map containing distances to nearest raster features and/or the value of the nearest non-null cell.

KEYWORDS

raster, distance, proximity

SYNOPSIS

r.grow.distance

r.grow.distance --help

r.grow.distance [-mn] input=name [distance=name] [value=name] [metric=string] [minimum_distance=float] [maximum_distance=float] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-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

Parameters:

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
minimum_distance=float: Minimum distance threshold
maximum_distance=float: Maximum distance threshold

DESCRIPTION
NOTES
EXAMPLES
- Distance from the streams network
- Distance from sea in meters in latitude-longitude CRS
SEE ALSO
AUTHOR

DESCRIPTION

r.grow.distance generates raster maps representing the distance to the nearest non-null cell in the input map and/or the value of the nearest non-null cell.

NOTES

The flag -n calculates the respective pixel distances to the nearest NULL cell.

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)

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 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)

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.

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

If minimum_distance is given, all cells with a distance smaller than minimum_distance will be set to NULL.

If maximum_distance is given, all cells with a distance larger than maximum_distance will be set to NULL. The resultant output is equivalent to a buffer.

If both minimum_distance and maximum_distance are given, the result will be similar to a doughnut, a restricted belt for a given distance range. All cells outside this distance range will be set to NULL.

EXAMPLES

Distance from the streams network

North Carolina sample dataset:

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

Euclidean distance from the streams network in meters (map subset)

Euclidean distance from the streams network in meters (detail, numbers shown with d.rast.num)

Distance from sea in meters in latitude-longitude CRS

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

Geodesic distances to sea in meters

AUTHOR

Glynn Clements

SOURCE CODE

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

Latest change: Wednesday Nov 27 22:53:26 2024 in commit: b90ce69e88409469369ec1edb86fde8ec822af8b