spDistsN1 function

Euclidean or Great Circle distance between points

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.

Returns

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

Author(s)

Roger Bivand, Edzer Pebesma

See Also

is.projected

Examples

ll <- matrix(c(5, 6, 60, 60), ncol=2)
km <- spDistsN1(ll, ll[1,], longlat=TRUE)
zapsmall(km)
utm32 <- matrix(c(276.9799, 332.7052, 6658.1572, 6655.2055), ncol=2)
spDistsN1(utm32, utm32[1,])
dg <- spDistsN1(ll, ll[1,])
dg
dg[2]/km[2]
data(meuse)
coordinates(meuse) <- c("x", "y")
res <- spDistsN1(meuse, meuse[1,])
summary(res)

p1 = SpatialPoints(cbind(1:3, 1:3))
spDists(p1)
spDists(p1, p1)
spDists(p1, p1, diagonal = TRUE)
try(spDists(p1, p1, segments = TRUE))
spDists(p1, segments = TRUE)
p2 = SpatialPoints(cbind(5:2, 2:5))
spDists(p1, p2)
try(spDists(p1, p2, diagonal = TRUE)) # fails
try(spDists(p1, p2, segments = TRUE)) # fails

# longlat points:
proj4string(p1) = "+proj=longlat +ellps=WGS84"
proj4string(p2) = "+proj=longlat +ellps=WGS84"
is.projected(p1)
is.projected(p2)
spDists(p1)
spDists(p1, p1)
spDists(p1, p1, diagonal = TRUE)
spDists(p1, p2)
try(spDists(p1, p2, diagonal = TRUE)) # fails
spDists(p1, p2[1:length(p1),], diagonal = TRUE)
spDists(p1, segments = TRUE)
spDists(p1[0],p2[0],diagonal=TRUE)
spDists(p1[0])

p1 = SpatialPoints(cbind(1:3, 1:3, 1:3))
spDists(p1)
spDists(p1, p1)
try(spDists(p1, p1, diagonal = TRUE))
try(spDists(p1, p1, segments = TRUE))
try(spDists(p1, segments = TRUE))
p2 = SpatialPoints(cbind(5:2, 2:5, 3:6))
spDists(p1, p2)
try(spDists(p1, p2, diagonal = TRUE)) # fails
try(spDists(p1, p2, segments = TRUE)) # fails