Distance between geometries

Calculates the distance between the given geometries

gDistance(spgeom1, spgeom2=NULL, byid=FALSE, hausdorff=FALSE, densifyFrac = NULL)
gWithinDistance(spgeom1, spgeom2=NULL, dist, byid=FALSE,
 hausdorff=FALSE, densifyFrac=NULL)

Arguments

spgeom1, spgeom2

sp objects as defined in package sp. If spgeom2 is NULL then spgeom1 is compared to itself.

byid

Logical vector determining if the function should be applied across ids (TRUE) or the entire object (FALSE) for spgeom1 and spgeom2

hausdorff

Logical determining if the discrete Hausdorff distance should be calculated

densifyFrac

Numerical value between 0 and 1 that determines the fraction by which to densify each segment of the geometry.

dist

Numerical value that determines cutoff distance

Value

gDistance by default returns the cartesian minimum distance between the two geometries in the units of the current projection. If hausdorff is TRUE then the Hausdorff distance is returned for the two geometries.

gWithinDistance returns TRUE if returned distance is less than or equal to the specified dist.

Details

Discrete Hausdorff distance is essentially a measure of the similarity or dissimilarity of the two geometries, see references below for more detailed explanations / descriptions.

If hausdorff is TRUE and densifyFrac is specified then the geometries' segments are densified by splitting each segment into equal length subsegments whose fraction of the total length is equal to densifyFrac.

Author

Roger Bivand & Colin Rundel

See also

gWithinDistance

References

Hausdorff Differences: https://en.wikipedia.org/wiki/Hausdorff_distance http://lin-ear-th-inking.blogspot.com/2009/01/computing-geometric-similarity.html

Examples

pt1 = readWKT("POINT(0.5 0.5)")
pt2 = readWKT("POINT(2 2)")

p1 = readWKT("POLYGON((0 0,1 0,1 1,0 1,0 0))")
p2 = readWKT("POLYGON((2 0,3 1,4 0,2 0))")

gDistance(pt1,pt2)
#> [1] 2.12132
gDistance(p1,pt1)
#> [1] 0
gDistance(p1,pt2)
#> [1] 1.414214
gDistance(p1,p2)
#> [1] 1


p3 = readWKT("POLYGON((0 0,2 0,2 2,0 2,0 0))")
p4 = readWKT("POLYGON((0 0,2 0,2 1.9,1.9 2,0 2,0 0))")
p5 = readWKT("POLYGON((0 0,2 0,2 1.5,1.5 2,0 2,0 0))")
p6 = readWKT("POLYGON((0 0,2 0,2 1,1 2,0 2,0 0))")
p7 = readWKT("POLYGON((0 0,2 0,0 2,0 0))")

gDistance(p3,hausdorff=TRUE)
#> [1] 0
gDistance(p3,p4,hausdorff=TRUE)
#> [1] 0.07071068
gDistance(p3,p5,hausdorff=TRUE)
#> [1] 0.3535534
gDistance(p3,p6,hausdorff=TRUE)
#> [1] 0.7071068
gDistance(p3,p7,hausdorff=TRUE)
#> [1] 1.414214