R/distance_from_sea.R

In EvolEcolGroup/pastclim: Manipulate Time Series of Palaeoclimate Reconstructions

#' Compute a raster of distances from the sea for each land pixel.
#'
#' Get the land mask for a dataset at a given time point, and compute distance
#' from the sea for each land pixel.
#'
#' @param time_bp time slice in years before present (negative)
#' @param time_ce time slice in years CE.
#' Only one of `time_bp` or `time_ce` should be used.
#' @param dataset string defining the dataset to use (a list of possible
#' values can be obtained with [list_available_datasets()]). This function
#' will not work on custom datasets.
#' @returns a [`terra::SpatRaster`] of distances from the coastline in km
#'
#' @import terra
#' @export

distance_from_sea <- function(time_bp = NULL, time_ce = NULL, dataset) {
  time_bp <- check_time_vars(time_bp = time_bp, time_ce = time_ce)
  times <- get_time_bp_steps(dataset = dataset)
  # if we don't give times, just use all available
  if (is.null(time_bp)) {
    time_bp <- times
  }
  # we use this to correctly convert time_bp
  time_index <- time_bp_to_i_series(
    time_bp = time_bp,
    time_steps = times
  )
  distances_list <- list()
  for (i in 1:length(time_index)) {
    this_time <- times[time_index[i]]
    this_land_mask <- get_land_mask(
      time_bp = this_time,
      dataset = dataset
    )
    coastlines_with_ice <- region_slice(
      time_bp = this_time,
      bio_variables = "biome",
      dataset = dataset
    )
    coastlines_with_ice[coastlines_with_ice > -1] <- 1
    coastlines_polyline <- terra::as.polygons(coastlines_with_ice) # first get polygon
    coastlines_polyline <- terra::as.lines(coastlines_polyline) # then extract line

    distances_rast <- terra::distance(this_land_mask[[1]],
      coastlines_polyline,
      unit = "km"
    )
    distances_rast <- terra::mask(distances_rast, this_land_mask)
    # browser()
    names(distances_rast) <- paste("distance_from_sea", time_bp(distances_rast), sep = "_")
    if (i == 1) {
      distances_all <- distances_rast
    } else {
      distances_all <- c(distances_all, distances_rast)
    }
  }
  varnames(distances_all) <- "distance_from_sea"
  return(distances_all)
}