rgeos (version 0.5-9)

# gDistance: Distance between geometries

## Description

Calculates the distance between the given geometries

## Usage

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

## 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`.

## 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

## Author

Roger Bivand & Colin Rundel

## 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`.

## References

`gWithinDistance`

## Examples

Run this code
``````

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)
gDistance(p1,pt1)
gDistance(p1,pt2)
gDistance(p1,p2)

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)
gDistance(p3,p4,hausdorff=TRUE)
gDistance(p3,p5,hausdorff=TRUE)
gDistance(p3,p6,hausdorff=TRUE)
gDistance(p3,p7,hausdorff=TRUE)
``````

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