R/rescale_raster.R

In choisy/sptools: Additional Functions for Spatial* Objects

#' Rescales the values of a raster as weights
#'
#' This function rescales the values of a raster between 0 and 1 so that they
#' sum to 1. These values can then be used as weights.
#'
#' @param rstr a RasterLayer object
#'
#' @return A RasterLayer object with values between 0 and 1 and summing to 1.
#'
#' @importFrom raster values values<-
#'
#' @export
#'
#' @examples
#' library(raster)
#' library(worldpopVN)
#' provinces <- sptools::gadm("vietnam", "sp", 1, intlib = FALSE, save = TRUE)
#' ppp2010 <- worldpopVN::getpop(2010)
#'
#' hanoi <- sptools::crop_on_poly(ppp2010, subset(provinces,
#'   VARNAME_1 == "Ha Noi"))
#'
#' # before rescaling:
#' sum(values(hanoi), na.rm = TRUE)
#'
#' # after rescaling:
#' sum(values(rescale_raster(hanoi)), na.rm = TRUE)
#'
rescale_raster <- function(rstr) {
  val <- values(rstr)
  values(rstr) <- val / sum(val, na.rm = TRUE)
  rstr
}