gedist {smerc}

Compute distance for geographic coordinates

Description

gedist computes the distance between the coordinates in x and y. If y isn't supplied, then the distances are computed between the coordinates in x alone. Otherwise, the pairwise distances between the points in x and y are computed. If longlat = TRUE, then the great circle distance is computed. eucdist is a simplified version of gedist that computes Euclidean distances alone while gcdist is a simplified version of gedist that computes great circle distance alone.

Usage

gedist(x, y = NULL, longlat = FALSE)

eucdist(x, y = NULL)

gcdist(x, y = NULL)

Arguments

x

A two-dimensional matrix of coordinates.

y

A two-dimensional matrix of coordinates.

longlat

A logical value indicating whether Euclidean distance (longlat = FALSE) or great circle distance (longlat = FALSE) should be computed. The default is longlat = FALSE.

Details

The algorithm used when longlat = TRUE is a C++ port of the C code written by Roger Bivand for the spDists function in the sp package, which appears to be based on a special case of the Vincenty formula with a slight correction based on the WGS84 flattening constant. See https://en.wikipedia.org/wiki/Great-circle_distance.

Value

A matrix of distances

Examples

coords = matrix(runif(10), ncol = 2)
# euclidean distance
d = gedist(coords)
all.equal(d, as.matrix(dist(coords)),
          check.attributes = FALSE)
all.equal(gedist(coords), eucdist(coords))

# great circle distance
all.equal(gedist(coords, longlat = TRUE),
          gcdist(coords))