Merge pull request #16 from baslat:polygon-voronoi

Polygon-voronoi

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: sak
 Title: The Swiss Army Knife of R
-Version: 0.9.0
+Version: 0.10.0
 Authors@R:
     person("Bas", "Latcham", , "[email protected]", role = c("aut", "cre"), comment = c(ORCID = "0000-0002-1733-7350"))
 Description: This is my personal package of helper functions. Like a Swiss

NAMESPACE

@@ -49,6 +49,7 @@ export(setup_yaml_megalinter)
 export(sg)
 export(show_linux_deps)
 export(st_intersection_quicker)
+export(st_no_overlap)
 export(standardise_geo_names)
 export(stopwatch)
 export(strip_geometry)

NEWS.md

@@ -1,3 +1,7 @@
+# sak 0.10.0
+
+- add `st_no_overlap()` to convert overlapping polygons into voronois
+
 # sak 0.9.0
 
 - adds `ch_add_stacked_labels()` by popular demand

R/st_no_overlap.R

@@ -0,0 +1,57 @@
+#' Non-overlapping polygons using Voronoi tesselation
+#'
+#' This function takes a set of polygons and returns a new set of polygons where
+#' the buffer zones of the original polygons do not overlap with each other.
+#' This is achieved by calculating the centroids of the polygons, creating a
+#' Voronoi tesselation around the centroids, and intersecting the Voronoi zones
+#' with the buffer zones of the original polygons. The resulting polygons do not
+#' overlap with each other, ensuring that they can be used for further analysis
+#' or visualization. Inspired by [this
+#' post](https://gis.stackexchange.com/questions/358797/splitting-overlap-between-polygons-and-assign-to-nearest-polygon-using-r)
+#'
+#' @param polygons A set of polygons with attributes.
+#'
+#' @return A set of polygons with attributes where the buffer zones of the original polygons do not overlap with each other.
+#'
+#' @details This function uses the `sf` package to calculate the centroids of
+#' the polygons using the `st_centroid` function, and to create a Voronoi
+#' tesselation around the centroids using the `st_voronoi` function. The Voronoi
+#' zones are then intersected with the buffer zones of the original polygons
+#' using the `st_intersection` function. The resulting polygons are returned
+#' with their original attributes.
+#'
+#' @export
+st_no_overlap <- function(polygons) {
+ # silence warning about constant attributes
+ sf::st_agr(polygons) <- "constant"
+ orig_crs <- sf::st_crs(polygons)
+	centroids <- sf::st_centroid(polygons)
+
+ # Voronoi tesselation
+	voronoi_raw <- centroids |>
+		sf::st_geometry() |>
+		sf::st_union() |>
+		# convert to meters crs
+		sf::st_transform(crs = 3857L) |>
+		sf::st_voronoi() |>
+		# convert back to original crs
+		sf::st_transform(crs = orig_crs) |>
+		sf::st_collection_extract()
+
+ # Put them back in their original order
+ voronoi <- voronoi_raw[unlist(sf::st_intersects(centroids, voronoi_raw))]
+
+	# Keep the attributes
+	result <- centroids
+
+	# Intersect voronoi zones with buffer zones
+ sf::st_geometry(result) <- purrr::map2(
+		polygons[["geometry"]],
+		voronoi,
+		sf::st_intersection
+	) |>
+  sf::st_sfc(crs = orig_crs)
+
+result
+
+}