R/track_distance.R

In traipse: Shared Tools for Tracking Data

#' Track distance
#'
#' Calculate geodesic distance on longitude, latitude input vectors. The unit of
#' distance is metres.
#'
#' By convention the first value is set to `NA` missing value, because the
#' distance applies to each sequential pair of locations.
#'
#' To use this on multiple track ids, use a grouped data frame with tidyverse
#' code like `data %>% group_by(id) %>% mutate(distance = track_distance(lon,
#' lat))`
#' @param x longitude
#' @param y latitude
#'
#' @return numeric vector of distances between sequential pairs of x, y in
#'   metres, see Details
#' @export
#'
#' @examples
#' track_distance(trips0$x, trips0$y)[1:10]
track_distance <- function(x, y) {
  c(NA_real_, geodist::geodist(cbind(x, y), sequential = TRUE, measure = "geodesic"))
}