R/hiking.R

In beerda/hexmatrix: What the Package Does (One Line, Title Case)

#' Tobler's hiking function
#'
#' A function that determines the hiking speed of a typical healthy adult person
#' while taking into account the slope angle.
#'
#' @param gradient dh/dx, i.e., a fraction of elevation difference over the
#'   horizontal distance (also a tangens of the slope angle)
#' @return a walking velocity in km/h
#' @references Tobler, Waldo (February 1993). Three presentations on
#'   geographical analysis and modeling: Non-isotropic geographic modeling
#'   speculations on the geometry of geography global spatial analysis.
#'   Technical Report. National center for geographic information and analysis.
#'   93 (1).
#' @references https://en.wikipedia.org/wiki/Tobler%27s_hiking_function
#'
#' @export
#'
#' @examples
#' # a maximum of 6 km/h corresponds to the downhill angle of 2.86 degrees
#' hiking(tanpi(-2.86/180))
#'
#' # speed on a path with flat surface
#' hiking(0)
hiking <- function(gradient) {
  assert_that(is.numeric(gradient))

  6 * exp((-3.5) * abs(gradient + 0.05))
}