r.distance - GRASS GIS manual

NAME

r.distance - Locates the closest points between objects in two raster maps.

KEYWORDS

SYNOPSIS

r.distance

r.distance --help

r.distance [-lon] map=name1,name2[,name1,name2,...] [separator=character] [sort=string] [--help] [--verbose] [--quiet] [--ui]

Flags:

-l: Include category labels in the output
-o: Report zero distance if rasters are overlapping
-n: Report null objects as *
--help: Print usage summary
--verbose: Verbose module output
--quiet: Quiet module output
--ui: Force launching GUI dialog

Parameters:

map=name1,name2[,name1,name2,...] [required]: Name of two input raster maps for computing inter-class distances
separator=character: Field separator; Special characters: pipe, comma, space, tab, newline; Default: :
sort=string: Sort output by distance; Default: sorted by categories; Options: asc, desc; asc: Sort by distance in ascending order; desc: Sort by distance in descending order

DESCRIPTION
- Flags
NOTES
SEE ALSO
AUTHOR

DESCRIPTION

r.distance locates the closest points between "objects" in two raster maps. An "object" is defined as all the grid cells that have the same category number, and closest means having the shortest "straight-line" distance. The cell centers are considered for the distance calculation (two adjacent grid cells have the distance between their cell centers).

The output is an ascii list, one line per pair of objects, in the following form:

cat1:cat2:distance:east1:north1:east2:north2

cat1: Category number from map1
cat2: Category number from map2
distance: The distance in meters between "cat1" and "cat2"
east1,north1: The coordinates of the grid cell "cat1" which is closest to "cat2"
east2,north2: The coordinates of the grid cell "cat2" which is closest to "cat1"

Flags

-l The -l flag outputs the category labels of the matched raster objects at the beginning of the line, if they exist.

-o The -o flag reports zero distance if the input rasters are overlapping.

NOTES

The output format lends itself to filtering. For example, to "see" lines connecting each of the category pairs in two maps, filter the output using awk and then into d.graph:

r.distance map=map1,map2 | \
  awk -F: '{print "move",$4,$5,"\ndraw",$6,$7}' | d.graph -m

To create a vector map of all the "map1" coordinates, filter the output into awk and then into v.in.ascii:

r.distance map=map1,map2 | \
  awk -F: '{print $4,$5}' | v.in.ascii format=point output=name separator=space

AUTHOR

Michael Shapiro, U.S. Army Construction Engineering Research Laboratory

SOURCE CODE

Available at: r.distance source code (history)

Accessed: Sunday Jan 22 07:36:08 2023