new function to calculate the distance between centroids of two spatr…

…asters

DESCRIPTION

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 Config/testthat/edition: 3
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 Roxygen: list(markdown = TRUE)
-RoxygenNote: 7.3.1
+RoxygenNote: 7.3.2

NAMESPACE

@@ -1,6 +1,7 @@
 # Generated by roxygen2: do not edit by hand
 
 export(area.calc)
+export(dist.centroids)
 export(load.data)
 export(spat.alpha)
 export(spat.alpha2)

R/dist_centroids.R

@@ -0,0 +1,79 @@
+#' Function to calculate distances between centroids of multiple SpatRasters
+#'
+#' @param ... N number of single or multilayer spatrasters
+#' @param ref Spatraster of reference
+#'
+#' @return A data frame with distance values
+#' @export
+#'
+#' @examples
+#' \donttest{
+#' library(terra)
+#' r1 <- terra::rast(system.file("extdata", "ref.tif",
+#' package = "divraster"))
+#' r2 <- terra::rast(system.file("extdata", "fut.tif",
+#' package = "divraster"))
+#' dist.centroids(r1, r2)
+#' }
+dist.centroids <- function(..., ref = 1) {
+  # Collect all SpatRasters into a list
+  rasters <- list(...)
+
+  # Ensure there are at least two SpatRasters
+  if (length(rasters) < 2) {
+    stop("At least two SpatRaster objects are required.")
+  }
+
+  # Ensure all SpatRasters have the same number of layers
+  n_layers <- terra::nlyr(rasters[[1]])
+  if (!all(sapply(rasters, terra::nlyr) == n_layers)) {
+    stop("All SpatRaster objects must have the same number of layers.")
+  }
+
+  # Initialize a list to store the distances for each layer
+  distances <- list()
+
+  # Get the base raster for comparison
+  base_raster <- rasters[[ref]]
+
+  # Loop over each layer
+  for (i in seq_len(n_layers)) {
+    # Extract the i-th layer from the base raster
+    base_layer <- base_raster[[i]]
+
+    # Convert base raster layer to binary and then to polygons
+    base_true <- base_layer == 1
+    base_polygons <- terra::as.polygons(base_true)
+    base_centroids <- terra::centroids(base_polygons)
+
+    # Initialize a data frame to store distances for this layer
+    dist_df <- data.frame(Layer = i)
+
+    # Loop over the other rasters and calculate distances
+    for (j in seq_along(rasters)) {
+      if (j != ref) {
+        # Extract the i-th layer from the current raster
+        current_layer <- rasters[[j]][[i]]
+
+        # Convert the current raster layer to binary and then to polygons
+        current_true <- current_layer == 1
+        current_polygons <- terra::as.polygons(current_true)
+        current_centroids <- terra::centroids(current_polygons)
+
+        # Calculate the distance between centroids of base and current raster layers
+        dist <- terra::distance(base_centroids, current_centroids, pairwise = FALSE, unit = "m")[2, 2]
+
+        # Add the distance to the data frame
+        dist_df[[paste0("Distance_r", ref, "_r", j)]] <- dist
+      }
+    }
+
+    # Store the distance data frame in the list
+    distances[[i]] <- dist_df
+  }
+
+  # Combine the list into a single data.frame
+  distances_df <- do.call(rbind, distances)
+
+  return(distances_df)
+}