Convert one or two rectangular objects containing lon-lat coordinates into vector or matrix of geodesic distances in metres.
geodist( x, y, paired = FALSE, sequential = FALSE, pad = FALSE, measure = "cheap" )
x | Rectangular object (matrix, |
---|---|
y | Optional second object which, if passed, results in distances
calculated between each object in |
paired | If |
sequential | If |
pad | If |
measure | One of "haversine" "vincenty", "geodesic", or "cheap" specifying desired method of geodesic distance calculation; see Notes. |
If only x
passed and sequential = FALSE
, a square
symmetric matrix containing distances between all items in x
; If only
x
passed and sequential = TRUE
, a vector of sequential
distances between rows of x
; otherwise if y
is passed, a matrix
of nrow(x)
rows and nrow(y)
columns. All return values are
distances in metres.
measure = "cheap"
denotes the mapbox cheap ruler
https://github.com/mapbox/cheap-ruler-cpp; measure = "geodesic"
denotes the very accurate geodesic methods given in Karney (2013)
"Algorithms for geodesics" J Geod 87:43-55, and as provided by the
codesf::st_dist() function.
n <- 50 # Default "cheap" distance measure is only accurate for short distances: x <- cbind (runif (n, -0.1, 0.1), runif (n, -0.1, 0.1)) y <- cbind (runif (2 * n, -0.1, 0.1), runif (2 * n, -0.1, 0.1)) colnames (x) <- colnames (y) <- c ("x", "y") d0 <- geodist (x) # A 50-by-50 matrix d1 <- geodist (x, y) # A 50-by-100 matrix d2 <- geodist (x, sequential = TRUE) # Vector of length 49 d2 <- geodist (x, sequential = TRUE, pad = TRUE) # Vector of length 50 d0_2 <- geodist (x, measure = "geodesic") # nanometre-accurate version of d0