Convert WorldClim GeoTIFF files to Esri ASCII Grid

wc_to_ascii() facilitates the conversion of one or more WorldClim GeoTIFF files to the Esri ASCII Grid raster format. Optionally, rasters can be cropped and/or aggregated using a provided polygon of class SpatVector.

Usage

wc_to_ascii(
  file,
  dir = dirname(file[1]),
  shape = NULL,
  box = NULL,
  dateline_fix = TRUE,
  extreme_outlier_fix = TRUE,
  aggregate = NULL,
  overwrite = TRUE,
  dx = -45,
  na_flag = -99,
  ...
)

Arguments

file: A character vector of file paths to the WorldClim GeoTIFF files to be converted. The files must have a .tif extension.
dir: A character vector specifying the output directory for the converted ASCII files (default: dirname(file[1])).
shape: (optional) A SpatVector object representing the polygon to crop the raster data. The function will crop the raster data to the extent of this polygon (default: NULL).
box: (optional) A numeric vector of length 4 specifying the bounding box for cropping the raster data in the format c(xmin, ymin, xmax, ymax) (default: NULL).
dateline_fix: (optional) A logical flag indicating whether to apply a dateline fix to the raster data. This is particularly useful when working with rasters and vectors that span the dateline (e.g. the Russian territory). See shift_and_crop to learn more (default: TRUE).
extreme_outlier_fix: (optional) A logical flag indicating whether to replace extreme outliers with NA. Extreme outliers are defined as values more than 10 times the interquartile range (IQR) below the first or above the third quartile. The quartiles and IQR are calculated using the unique (deduplicated) values of the data, and the resulting thresholds are applied to the full dataset. This helps remove abnormal values in raster data.
aggregate: (optional) An integer value specifying the aggregation factor. The function will aggregate the raster data by this factor. See aggregate() for more details (default: NULL).
overwrite: (optional) A logical flag indicating whether to overwrite existing files in the output directory (default: TRUE).
dx: (optional) A numeric value specifying the horizontal distance in degrees to shift the raster data. This is only relevant if dateline_fix is set to TRUE (default: -45).
na_flag: (optional) An integer value specifying the NoData value for the output ASCII files. See the Details section to learn more (default: -99).
...: Additional arguments passed to writeRaster() for writing the ASCII files.

Value

A character vector containing the file paths of the converted ASCII files.

Details

`na_flag` parameter

According to the Esri ASCII raster format documentation, the default value for NODATA_VALUE (the NA flag) is -9999. However, using four digits of precision significantly inflates file size. For WorldClim data, two significant digits (-99) are sufficient, since the only variables with negative values are temperatures, and the lowest temperature ever recorded on Earth is above that.

Examples

if (FALSE) { # \dontrun{
  library(curl)
  library(fs)
  library(magrittr)
  library(readr)
  library(rvest)
  library(stringr)
  library(zip)

  # Download the WorldClim Data

  url <-
    get_wc_url("hcd") |>
    rvest::read_html() |>
    rvest::html_elements("a") |>
    rvest::html_attr("href") |>
    stringr::str_subset("geodata") |>
    magrittr::extract(1)

  zip_file <- basename(url)

  curl::curl_download(url, path(tempdir(), zip_file))

  path(tempdir(), zip_file) |>
    zip::unzip(exdir = tempdir())

  tif_file <-
    dir_ls(tempdir(), regexp = "\\.tif$") |>
    magrittr::extract(1)

  # Run the Function

  asc_file <- tif_file |> wc_to_ascii()

  # Check the Output

  asc_file |> read_lines(n_max = 6)
} # }