#' CONTIG_MN (landscape level)
#'
#' @description Mean of Contiguity index (Shape metric)
#'
#' @param landscape A categorical raster object: SpatRaster; Raster* Layer, Stack, Brick; stars or a list of SpatRasters.
#' @param directions The number of directions in which patches should be connected: 4 (rook's case) or 8 (queen's case).
#'
#' @details
#' \deqn{CONTIG_{MN} = mean(CONTIG[patch_{i}])}
#'
#' where \eqn{CONTIG[patch_{ij}]} is the contiguity of each patch.
#'
#' CONTIG_MN is a 'Shape metric'. It summarises the landscape as the mean of all patches
#' in the landscape. CONTIG_MN asses the spatial connectedness (contiguity) of
#' cells in patches. The metric coerces patch values to a value of 1 and the background
#' to NA. A nine cell focal filter matrix:
#'
#' ```
#' filter_matrix <- matrix(c(1, 2, 1,
#' 2, 1, 2,
#' 1, 2, 1), 3, 3, byrow = T)
#' ```
#' ... is then used to weight orthogonally contiguous pixels more heavily than
#' diagonally contiguous pixels. Therefore, larger and more connections between
#' patch cells in the rookie case result in larger contiguity index values.
#'
#' \subsection{Units}{None}
#' \subsection{Range}{0 >= CONTIG_MN <= 1}
#' \subsection{Behaviour}{CONTIG equals the mean of the contiguity index on landscape level for all
#' patches.}
#'
#' @seealso
#' \code{\link{lsm_p_contig}},
#' \code{\link{lsm_c_contig_sd}},
#' \code{\link{lsm_c_contig_cv}},
#' \code{\link{lsm_c_contig_mn}}, \cr
#' \code{\link{lsm_l_contig_sd}},
#' \code{\link{lsm_l_contig_cv}}
#'
#' @return tibble
#'
#' @examples
#' landscape <- terra::rast(landscapemetrics::landscape)
#' lsm_l_contig_mn(landscape)
#'
#' @references
#' McGarigal K., SA Cushman, and E Ene. 2023. FRAGSTATS v4: Spatial Pattern Analysis
#' Program for Categorical Maps. Computer software program produced by the authors;
#' available at the following web site: https://www.fragstats.org
#'
#' LaGro, J. 1991. Assessing patch shape in landscape mosaics.
#' Photogrammetric Engineering and Remote Sensing, 57(3), 285-293
#'
#' @export
lsm_l_contig_mn <- function(landscape, directions = 8) {
landscape <- landscape_as_list(landscape)
result <- lapply(X = landscape,
FUN = lsm_l_contig_mn_calc,
directions = directions)
layer <- rep(seq_along(result),
vapply(result, nrow, FUN.VALUE = integer(1)))
result <- do.call(rbind, result)
tibble::add_column(result, layer, .before = TRUE)
}
lsm_l_contig_mn_calc <- function(landscape, directions, extras = NULL) {
contig_patch <- lsm_p_contig_calc(landscape,
directions = directions,
extras = extras)
# all values NA
if (all(is.na(contig_patch$value))) {
return(tibble::new_tibble(list(level = "landscape",
class = as.integer(NA),
id = as.integer(NA),
metric = "contig_mn",
value = as.double(NA))))
}
contig_mn <- mean(contig_patch$value)
return(tibble::new_tibble(list(level = rep("landscape", length(contig_mn)),
class = rep(as.integer(NA), length(contig_mn)),
id = rep(as.integer(NA), length(contig_mn)),
metric = rep("contig_mn", length(contig_mn)),
value = as.double(contig_mn))))
}
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