R/tile.R

In r-spatial/stars: Spatiotemporal Arrays, Raster and Vector Data Cubes

#' Specify parameters to load raster in blocks
#'
#' Helper function for specifying the block parameters (\code{nXOff},
#' \code{nYOff}, \code{nXsize}, and \code{nYSize}) required by \code{RasterIO}
#' argument in \link{read_stars}
#'
#' @param img_rows number of input raster rows (integer)
#' @param img_cols number of input raster columns (integer)
#' @param x_window number of rows in block (integer)
#' @param y_window number of columns in block (integer)
#' @param overlap number of overlapping pixels (integer)
#'
#' @return matrix with specified \code{nXOff}, \code{nYOff}, \code{nXsize},
#' and \code{nYSize} parameters for every block
#'
#' @examples
#' \dontrun{
#' tif = system.file("tif/L7_ETMs.tif", package = "stars")
#' r = read_stars(tif, proxy = TRUE)
#' tiles = st_tile(nrow(r), ncol(r), 256, 256)
#' for (i in seq_len(nrow(tiles))) {
#'   tile = read_stars(tif, proxy = FALSE, RasterIO = tiles[i, ])
#'   # write tiles to separate files
#'   write_stars(tile, dsn = paste0(i, ".tif"))
#' }
#' }
#'
#' @export
st_tile = function(img_rows, img_cols, x_window, y_window, overlap = 0) {

	# make sure input values are integers
	img_rows = as.integer(img_rows)
	img_cols = as.integer(img_cols)
	x_window = as.integer(x_window)
	y_window = as.integer(y_window)
	overlap = as.integer(overlap)

	n = ceiling((img_rows / x_window)) * ceiling((img_cols / y_window))

	x_vec = y_vec = integer(n)
	nXSize_vec = nYSize_vec = integer(n)

	i = 1L
	for (x in seq.int(1L, img_rows, y_window)) {

		if (x + y_window + overlap <= img_rows) {
			nXSize = y_window + overlap
		} else {
			nXSize = img_rows - x + 1L
		}

		for (y in seq.int(1L, img_cols, x_window)) {

			if (y + x_window + overlap <= img_cols) {
				nYSize = x_window + overlap
			} else {
				nYSize = img_cols - y + 1L
			}

			x_vec[i] = x
			y_vec[i] = y
			nXSize_vec[i] = nXSize
			nYSize_vec[i] = nYSize
			i = i + 1L
		}

	}

	mat = matrix(c(x_vec, y_vec, nXSize_vec, nYSize_vec), ncol = 4)
	colnames(mat) = c("nXOff", "nYOff", "nXSize", "nYSize")

	return(mat)

}