Euclidean or Great Circle distance between points — spDistsN1 • sp

The function returns a vector of distances between a matrix of 2D points, first column longitude, second column latitude, and a single 2D point, using Euclidean or Great Circle distance (WGS84 ellipsoid) methods.

spDistsN1(pts, pt, longlat = FALSE)
spDists(x, y = x, longlat = FALSE, segments = FALSE, diagonal = FALSE)

Arguments

pts	A matrix of 2D points, first column x/longitude, second column y/latitude, or a SpatialPoints or SpatialPointsDataFrame object
pt	A single 2D point, first value x/longitude, second value y/latitude, or a SpatialPoints or SpatialPointsDataFrame object with one point only
x	A matrix of n-D points with row denoting points, first column x/longitude, second column y/latitude, or a Spatial object that has a coordinates method
y	A matrix of n-D points with row denoting points, first column x/longitude, second column y/latitude, or a Spatial object that has a coordinates method
longlat	logical; if FALSE, Euclidean distance, if TRUE Great Circle (WGS84 ellipsoid) distance; if `x` is a Spatial object, longlat should not be specified but will be derived from is.projected`(x)`
segments	logical; if `TRUE`, `y` must be missing; the vector of distances between consecutive points in `x` is returned.
diagonal	logical; if `TRUE`, `y` must be given and have the same number of points as `x`; the vector with distances between points with identical index is returned.

Value

spDistsN1 returns a numeric vector of distances in the metric of the points if longlat=FALSE, or in kilometers if longlat=TRUE.

spDists returns a full matrix of distances in the metric of the points if longlat=FALSE, or in kilometers if longlat=TRUE; it uses spDistsN1 in case points are two-dimensional. In case of spDists(x,x), it will compute all n x n distances, not the sufficient n x (n-1).

Note

The function can also be used to find a local kilometer equivalent to a plot scaled in decimal degrees in order to draw a scale bar.

References

http://www.abecedarical.com/javascript/script_greatcircle.html

See also

Examples

ll <- matrix(c(5, 6, 60, 60), ncol=2)
km <- spDistsN1(ll, ll[1,], longlat=TRUE)
zapsmall(km)
#> [1]  0.00000 55.79918
utm32 <- matrix(c(276.9799, 332.7052, 6658.1572, 6655.2055), ncol=2)
spDistsN1(utm32, utm32[1,])
#> [1]  0.00000 55.80342
dg <- spDistsN1(ll, ll[1,])
dg
#> [1] 0 1
dg[2]/km[2]
#> [1] 0.01792141
data(meuse)
coordinates(meuse) <- c("x", "y")
res <- spDistsN1(meuse, meuse[1,])
summary(res)
#>    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
#>       0    1210    2279    2282    3403    4425 

p1 = SpatialPoints(cbind(1:3, 1:3))
spDists(p1)
#>          [,1]     [,2]     [,3]
#> [1,] 0.000000 1.414214 2.828427
#> [2,] 1.414214 0.000000 1.414214
#> [3,] 2.828427 1.414214 0.000000
spDists(p1, p1)
#>          [,1]     [,2]     [,3]
#> [1,] 0.000000 1.414214 2.828427
#> [2,] 1.414214 0.000000 1.414214
#> [3,] 2.828427 1.414214 0.000000
spDists(p1, p1, diagonal = TRUE)
#> [1] 0 0 0
try(spDists(p1, p1, segments = TRUE))
#> Error in spDists(p1, p1, segments = TRUE) : missing(y) is not TRUE
spDists(p1, segments = TRUE)
#> [1] 1.414214 1.414214
p2 = SpatialPoints(cbind(5:2, 2:5))
spDists(p1, p2)
#>          [,1]     [,2]     [,3]     [,4]
#> [1,] 4.123106 3.605551 3.605551 4.123106
#> [2,] 3.000000 2.236068 2.236068 3.000000
#> [3,] 2.236068 1.000000 1.000000 2.236068
try(spDists(p1, p2, diagonal = TRUE)) # fails
#> Error in spDists(p1, p2, diagonal = TRUE) : 
#>   nrow(x) == nrow(y) is not TRUE
try(spDists(p1, p2, segments = TRUE)) # fails
#> Error in spDists(p1, p2, segments = TRUE) : missing(y) is not TRUE

# longlat points:
proj4string(p1) = "+proj=longlat +ellps=WGS84"
#> Warning: Discarded datum Unknown based on WGS84 ellipsoid in CRS definition
proj4string(p2) = "+proj=longlat +ellps=WGS84"
#> Warning: Discarded datum Unknown based on WGS84 ellipsoid in CRS definition
is.projected(p1)
#> [1] FALSE
is.projected(p2)
#> [1] FALSE
spDists(p1)
#>          [,1]     [,2]     [,3]
#> [1,]   0.0000 156.8744 313.7019
#> [2,] 156.8744   0.0000 156.8276
#> [3,] 313.7019 156.8276   0.0000
spDists(p1, p1)
#>          [,1]     [,2]     [,3]
#> [1,]   0.0000 156.8744 313.7019
#> [2,] 156.8744   0.0000 156.8276
#> [3,] 313.7019 156.8276   0.0000
spDists(p1, p1, diagonal = TRUE)
#> [1] 0 0 0
spDists(p1, p2)
#>          [,1]     [,2]     [,3]     [,4]
#> [1,] 458.6486 400.3590 399.3794 456.0565
#> [2,] 333.7564 248.3940 247.5177 331.7324
#> [3,] 248.3940 111.1679 110.5772 247.4690
try(spDists(p1, p2, diagonal = TRUE)) # fails
#> Error in spDists(p1, p2, diagonal = TRUE) : 
#>   nrow(x) == nrow(y) is not TRUE
spDists(p1, p2[1:length(p1),], diagonal = TRUE)
#> [1] 458.6486 248.3940 110.5772
spDists(p1, segments = TRUE)
#> [1] 156.8744 156.8276
spDists(p1[0],p2[0],diagonal=TRUE)
#> numeric(0)
spDists(p1[0])
#> <0 x 0 matrix>

p1 = SpatialPoints(cbind(1:3, 1:3, 1:3))
spDists(p1)
#>          1        2        3
#> 1 0.000000 1.732051 3.464102
#> 2 1.732051 0.000000 1.732051
#> 3 3.464102 1.732051 0.000000
spDists(p1, p1)
#>          [,1]     [,2]     [,3]
#> [1,] 0.000000 1.732051 3.464102
#> [2,] 1.732051 0.000000 1.732051
#> [3,] 3.464102 1.732051 0.000000
try(spDists(p1, p1, diagonal = TRUE))
#> Error in spDists(p1, p1, diagonal = TRUE) : ncol(x) == 2 is not TRUE
try(spDists(p1, p1, segments = TRUE))
#> Error in spDists(p1, p1, segments = TRUE) : missing(y) is not TRUE
try(spDists(p1, segments = TRUE))
#> Error in spDists(p1, segments = TRUE) : ncol(x) == 2 is not TRUE
p2 = SpatialPoints(cbind(5:2, 2:5, 3:6))
spDists(p1, p2)
#>          [,1]     [,2]     [,3]     [,4]
#> [1,] 4.582576 4.690416 5.385165 6.480741
#> [2,] 3.162278 3.000000 3.741657 5.000000
#> [3,] 2.236068 1.414214 2.236068 3.741657
try(spDists(p1, p2, diagonal = TRUE)) # fails
#> Error in spDists(p1, p2, diagonal = TRUE) : ncol(x) == 2 is not TRUE
try(spDists(p1, p2, segments = TRUE)) # fails
#> Error in spDists(p1, p2, segments = TRUE) : missing(y) is not TRUE