volcano_stars.R

#' Retrieve a stars layer of Auckland’s Maunga Whau volcano topography.  Adapted from
#' USGS-R inlmisc package.
#'
#' @seealso \url{https://waterdata.usgs.gov/blog/inlmiscmaps/}
#' @seealso \url{https://CRAN.R-project.org/package=inlmisc}
#' @export
#' @param indexed logical, if TRUE then assign 1,2,3,... as cell values
#' @return Stars
volcano_stars <- function(indexed = FALSE){
  require(magrittr)
  require(stars)
  m <- datasets::volcano
  s <- 10
  x0 <- 6478705
  y0 <- 2668010
  d <- dim(m)
  m <- m[,rev(seq_len(d[2]))]
  x <- seq(from = x0, length.out = d[2], by = s)
  y <- seq(from = y0 , length.out = d[1], by = -s)
  r <- stars::st_as_stars(m) %>%
    stars::st_set_dimensions(names = c("x", "y")) %>%
    stars::st_set_dimensions("x", offset = x0, delta = s) %>%
    stars::st_set_dimensions("y", offset = y0, delta = -s) %>%
    sf::st_set_crs("epsg:27200") 
  
  if (indexed){
    r[[1]] <- matrix(seq_len(prod(d)), nrow = d[1], ncol = d[2], byrow = TRUE)
  }
  r
}