## 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

## SEE ALSO

r.buffer, r.cost, r.drain, r.grow, r.grow.distance, v.distance

## AUTHOR

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