add: new merge type in st_merge_spatialunits

add: plots in st_surveyspatialunits fix: logic issues in st_create_tessellations
anirudhgovind · Feb 11, 2024 · 8baa6f8 · 8baa6f8
1 parent 8f111da
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diff --git a/DESCRIPTION b/DESCRIPTION
@@ -14,6 +14,7 @@ URL: https://github.com/anirudhgovind/multi,
 BugReports: https://github.com/anirudhgovind/multi/issues
 Imports: 
     dplyr (>= 1.0.9),
+    graphics,
     lwgeom (>= 0.2.8),
     sf (>= 1.0.8),
     sfdep,

diff --git a/R/st_create_tessellations.R b/R/st_create_tessellations.R
@@ -11,7 +11,7 @@
 #' size for a spatial unit. Contiguous units will be iteratively merged until
 #' this value is reached. To skip this process, set `merge_threshold = NULL`.
 #' See st_merge_spatialunits() for more details.
-#' @param merge_type string; Passed on to st_merge_spatialunits.
+#' @param merge_type string; Passed on to st_merge_spatialunits().
 #' Criteria with which polygons are merged. Must be one of
 #' "min_centroid_distance", "min_shared_boundary", or "max_shared_boundary".
 #' Default = "min_centroid_distance".
@@ -38,7 +38,7 @@
 st_create_tessellations <-
   function(x,
            boundary,
-           type = c("morphological"),
+           type = "morphological",
            segment_length = 0.5,
            shrink_extent = 0.4,
            merge_threshold = NULL,
@@ -164,10 +164,14 @@ st_create_tessellations <-
         )
       }
 
-      # Convert CRS back to original
+      # If geometry is long lat, convert CRS back to the original.
 
-      tessellations <- sf::st_transform(tessellations,
-                                        x_crs)
+      if (sf::st_is_longlat(x) == TRUE |
+          sf::st_is_longlat(boundary) == TRUE) {
+
+        tessellations <- sf::st_transform(tessellations,
+                                          x_crs)
+      }
 
       return(tessellations)
     } else {

diff --git a/R/st_merge_spatialunits.R b/R/st_merge_spatialunits.R
@@ -7,7 +7,7 @@
 #' iteratively merged until this value is reached. To skip this process,
 #' set `merge_threshold = NULL`.
 #' @param merge_type string; criteria with which polygons are merged. Must be one of
-#' "min_centroid_distance", "min_shared_boundary", or "max_shared_boundary".
+#' "min_centroid_distance", "min_adjacent_area", "max_adjacent_area", "min_shared_boundary", or "max_shared_boundary".
 #' Default = "min_centroid_distance".
 #' @param contiguity string; one of "queen" or "rook". Default = "rook".
 #' @param verbose logical; if `FALSE` no status messages will be output.
@@ -43,11 +43,15 @@ st_merge_spatialunits <- function(x,
 
   # Check type is one of defined defaults
 
-  if (!merge_type %in% c("min_centroid_distance",
-                         "min_shared_boundary",
-                         "max_shared_boundary")) {
+  if (!merge_type %in% c(
+    "min_centroid_distance",
+    "min_adjacent_area",
+    "max_adjacent_area",
+    "min_shared_boundary",
+    "max_shared_boundary"
+  )) {
     stop(
-      "merge_type must be one of 'min_centroid_distance', 'min_shared_boundary', or 'max_shared_boundary'."
+      "merge_type must be one of 'min_centroid_distance', 'min_adjacent_area', 'max_adjacent_area', 'min_shared_boundary', or 'max_shared_boundary'."
     )
   }
 
@@ -112,6 +116,13 @@ st_merge_spatialunits <- function(x,
         if (merge_type == "min_centroid_distance") {
           selected_unit <- min_centroid_distance(ref_unit = ref_unit,
                                                  ref_unit_neighbours_geo = ref_unit_neighbours_geo)
+        } else if (merge_type == "min_adjacent_area" |
+                   merge_type == "max_adjacent_area") {
+          selected_unit <- area_adjacency(
+            ref_unit = ref_unit,
+            ref_unit_neighbours_geo = ref_unit_neighbours_geo,
+            merge_type = merge_type
+          )
         } else if (merge_type == "min_shared_boundary" |
                    merge_type == "max_shared_boundary") {
           selected_unit <- shared_boundary_length(
@@ -166,6 +177,36 @@ st_merge_spatialunits <- function(x,
   return(x)
 }
 
+# Function to merge polygon with an adjacent polygon with the smallest/ largest area
+
+area_adjacency <- function(ref_unit,
+                           ref_unit_neighbours_geo,
+                           merge_type = merge_type) {
+  # Init Var
+
+  areas <- NULL
+
+  # Find areas of the polygons
+  areas <- sf::st_area(ref_unit_neighbours_geo)
+
+  # If min area
+  if (merge_type == "min_adjacent_area") {
+    smallest_area <-
+      as.integer(ref_unit_neighbours_geo$index[which.min(areas)])
+
+    return(smallest_area)
+  }
+
+  # If max area
+  if (merge_type == "max_adjacent_area") {
+    largest_area <-
+      as.integer(ref_unit_neighbours_geo$index[which.max(areas)])
+
+    return(largest_area)
+  }
+
+}
+
 # Function to select polygon based on minimum centroid distance
 
 min_centroid_distance <- function(ref_unit,

diff --git a/R/st_survey_spatialunits.R b/R/st_survey_spatialunits.R
@@ -3,7 +3,8 @@
 #' @param x an `sf` object with `POLYGON` geometries representing the
 #' spatial units to be surveyed.
 #' @param trim numeric; fraction (0 to 0.5) of values to be trimmed from the lower
-#' end to compute a trimmed mean
+#' end to compute a trimmed mean.
+#' @param viz binary; Displays a scatterplot of area distributions.
 #'
 #' @return A `data.frame` object with numeric values of min, max, mean, and
 #' median.
@@ -15,7 +16,13 @@
 #' survey_report <- st_survey_spatialunits(x = street_blocks)
 #' survey_report
 st_survey_spatialunits <- function(x,
-                                   trim = NULL) {
+                                   trim = NULL,
+                                   viz = TRUE) {
+
+  # Init var for later
+
+  areas <- NULL
+
   # Check x is of type sf
 
   if (!inherits(x, "sf")) {
@@ -25,7 +32,8 @@ st_survey_spatialunits <- function(x,
   # Check geometry types
 
   if (all(sf::st_is(x,
-                    "POLYGON") != TRUE)) {
+                    c("POLYGON",
+                      "MULTIPOLYGON")) != TRUE)) {
     stop("x must contain `POLYGON` geometries.")
   }
 
@@ -42,10 +50,11 @@ st_survey_spatialunits <- function(x,
 
   # Survey Result
 
-  output <- data.frame(category = c("Area",
-                                    "Area",
-                                    "Area",
-                                    "Area"),
+  output <- data.frame(
+    category = c("Area",
+                 "Area",
+                 "Area",
+                 "Area"),
     description = c("Min",
                     "Max",
                     "Mean",
@@ -67,16 +76,52 @@ st_survey_spatialunits <- function(x,
         dplyr::slice_tail(prop = 1 - trim) |>
         dplyr::summarise(value = mean(areas))
 
-      suffix <- data.frame(category = c("Area"),
-                           description = c(paste0("Trimmed Mean (",
-                                                  trim,
-                                                  ")")),
-                           value = c(x_trim))
+      suffix <- data.frame(
+        category = c("Area"),
+        description = c(paste0("Trimmed Mean (",
+                               trim,
+                               ")")),
+        value = c(x_trim)
+      )
 
       output <- rbind(output,
                       suffix)
     }
   }
+
+  if (viz == TRUE) {
+    plot(x$areas,
+         col = "gray",
+         xlab = "Spatial Unit Index",
+         ylab = "Areas")
+    graphics::abline(h = c(x_min,
+                           x_max,
+                           x_mean,
+                           x_median),
+                     lty = 2)
+    graphics::text(
+      x = c(0,
+            nrow(x),
+            0,
+            nrow(x)),
+      y = c(x_min,
+            x_max,
+            x_mean,
+            x_median),
+      labels = c("min",
+                 "max",
+                 "mean",
+                 "median")
+    )
+    if (!is.null(trim)) {
+      graphics::abline(h = x_trim,
+                       col = "black")
+      graphics::text(x = nrow(x) / 2,
+                     y = x_trim,
+                     labels = "trimmed mean")
+    }
+  }
+
   print(output,
         right = FALSE)
 }
diff --git a/man/st_create_tessellations.Rd b/man/st_create_tessellations.Rd
diff --git a/man/st_merge_spatialunits.Rd b/man/st_merge_spatialunits.Rd
diff --git a/man/st_survey_spatialunits.Rd b/man/st_survey_spatialunits.Rd
diff --git a/vignettes/articles/1-Spatial-Units.Rmd b/vignettes/articles/1-Spatial-Units.Rmd
@@ -21,7 +21,7 @@ tmap::tmap_options(check.and.fix = TRUE,
                    show.warnings = FALSE)
 ```
 
-`multi` simplifies the process of creating morphological spatial units like street blocks and morphological tessellation units (MTs; Fleischmann et al., 2020). This vignette presents one workflow for creating street blocks and MTs using data from OpenStreetMap (using the excellent `osmdata` package; Padgham et al., 2022) with Bangalore, India as a case. 
+`multi` simplifies the process of creating morphological spatial units like street blocks and morphological tessellation units (MTs; Fleischmann et al., 2020). This vignette presents one workflow for creating street blocks and MTs using data from OpenStreetMap (sourced using the excellent `osmdata` package; Padgham et al., 2022) with Bangalore, India as a case. 
 
 ## Street Blocks