R/grid_cellsize.R

In tidysdm: Species Distribution Models with Tidymodels

#' Get default grid cellsize for a given dataset
#'
#' This function facilitates using [spatialsample::spatial_block_cv] multiple
#' times in an analysis. [spatialsample::spatial_block_cv] creates a grid based
#' on the object in `data`. However, if spatial blocks are generated multiple
#' times in an analysis (e.g. for a [spatial_initial_split()], and then
#' subsequently for cross-validation on the training dataset), it might be
#' desirable to keep the same grid). By applying this function to the largest
#' dataset, usually the full dataset before [spatial_initial_split()]. The
#' resulting cellsize can be used as an option in
#' [spatialsample::spatial_block_cv].
#' @param data a [sf::sf] dataset used to size the grid
#' @param n the number of cells in the grid, defaults to c(10,10), which is also
#'   the default for [sf::st_make_grid()]
#' @returns the cell size
#' @export

grid_cellsize <- function(
    data,
    n = c(10, 10)) {
  # TODO check that this is an sf object
  grid_box <- sf::st_bbox(data)
  if (is_longlat(data)) {
    grid_box <- expand_grid(grid_box)
  }
  c(
    diff(sf::st_bbox(grid_box)[c(1, 3)]),
    diff(sf::st_bbox(grid_box)[c(2, 4)])
  ) / n
}