gDistance | R Documentation |

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)
```

`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 |

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`

.

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`

.

Roger Bivand & Colin Rundel

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

`gWithinDistance`

```
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)
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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