add area intersection weights

DESCRIPTION

@@ -12,7 +12,7 @@ BugReports: https://github.com/USGS-R/ncdfgeom/issues
 Imports: RNetCDF, ncmeta, sf, dplyr, methods, stars
 Depends:
   R (>= 3.5)
-Suggests: testthat, knitr, rmarkdown, pkgdown, geoknife, ncdf4, jsonlite
+Suggests: testthat, knitr, rmarkdown, pkgdown, geoknife, ncdf4, jsonlite, areal
 License: CC0
 Encoding: UTF-8
 VignetteBuilder: knitr

NAMESPACE

 # Generated by roxygen2: do not edit by hand
 
+export(calculate_area_intersection_weights)
 export(create_cell_geometry)
 export(read_attribute_data)
 export(read_geometry)
@@ -20,13 +21,17 @@ importFrom(RNetCDF,var.inq.nc)
 importFrom(RNetCDF,var.put.nc)
 importFrom(dplyr,filter)
 importFrom(dplyr,group_by)
+importFrom(dplyr,mutate)
+importFrom(dplyr,right_join)
 importFrom(dplyr,select)
+importFrom(dplyr,ungroup)
 importFrom(methods,is)
 importFrom(ncmeta,nc_atts)
 importFrom(ncmeta,nc_axes)
 importFrom(ncmeta,nc_dim)
 importFrom(ncmeta,nc_meta)
 importFrom(sf,"st_crs<-")
+importFrom(sf,st_area)
 importFrom(sf,st_as_sf)
 importFrom(sf,st_bbox)
 importFrom(sf,st_buffer)
@@ -36,6 +41,7 @@ importFrom(sf,st_coordinates)
 importFrom(sf,st_crs)
 importFrom(sf,st_geometry)
 importFrom(sf,st_geometry_type)
+importFrom(sf,st_intersection)
 importFrom(sf,st_join)
 importFrom(sf,st_linestring)
 importFrom(sf,st_multilinestring)

R/calculate_area_intersection_weights.R

+#' Area Weighted Intersection (areal implementation)
+#' @description Returns the fractional percent of each
+#' feature in x that is covered by each intersecting feature
+#' in y. These can be used as the weights in an area-weighted
+#' mean overlay analysis where x is the data source and area-
+#' weighted means are being generated for the target, y.
+#'
+#' This function is a lightwieght wrapper around the functions
+#' \link[areal]{aw_intersect} \link[areal]{aw_total} and \link[areal]{aw_weight}
+#' from the \href{https://github.com/slu-openGIS/areal}{areal package}.
+#'
+#' @param x sf data.frame source features including one geometry column and one identifier column
+#' @param y sf data.frame target features including one geometry column and one identifier column
+#' @param allow_lonlat boolean If FALSE (the default) lon/lat target features are not allowed.
+#' Intersections in lon/lat are generally not valid and problematic at the international date line.
+#' @return data.frame containing fraction of each feature in x that is
+#' covered by each feature in y. e.g. If a feature from x is entirely within a feature in y,
+#' w will be 1. If a feature from x is 50% in one feature for y and 50% in another, there
+#' will be two rows, one for each x/y pair of features with w = 0.5 in each.
+#'
+#' @examples
+#' b1 = sf::st_polygon(list(rbind(c(-1,-1), c(1,-1),
+#'                            c(1,1), c(-1,1),
+#'                            c(-1,-1))))
+#' b2 = b1 + 2
+#' b3 = b1 + c(-0.2, 2)
+#' b4 = b1 + c(2.2, 0)
+#' b = sf::st_sfc(b1, b2, b3, b4)
+#' a1 = b1 * 0.8
+#' a2 = a1 + c(1, 2)
+#' a3 = a1 + c(-1, 2)
+#' a = sf::st_sfc(a1,a2,a3)
+#' plot(b, border = 'red')
+#' plot(a, border = 'green', add = TRUE)
+#'
+#' sf::st_crs(b) <- sf::st_crs(a) <- sf::st_crs(5070)
+#'
+#' b <- sf::st_sf(b, data.frame(idb = c(1, 2, 3, 4)))
+#' a <- sf::st_sf(a, data.frame(ida = c(1, 2, 3)))
+#'
+#' sf::st_agr(a) <- sf::st_agr(b) <- "constant"
+#'
+#' a_b <- calculate_area_intersection_weights(a, b)
+#' b_a <- calculate_area_intersection_weights(b, a)
+#'
+#' @export
+#' @importFrom sf st_intersection st_set_geometry st_area st_crs
+#' @importFrom dplyr mutate group_by right_join select ungroup
+
+calculate_area_intersection_weights <- function(x, y, allow_lonlat = FALSE) {
+
+  if(!requireNamespace("areal")) stop("areal package required for intersection weights")
+  
+  if (st_crs(x) != st_crs(y)) {
+    x <- st_transform(x, st_crs(y))
+  }
+
+  if(st_crs(y)$proj == "longlat" & !allow_lonlat) {
+    stop("Found lon/lat coordinates and allow_lonlat is FALSE.")
+  }
+
+  # Standard evaluation is for chumps.
+  id_x <- names(x)[names(x) != attr(x, "sf_column")]
+  id_y <- names(y)[names(y) != attr(y, "sf_column")]
+
+  # There is a bug in areal and this works around it.
+  geom_name_x <- attr(x, "sf_column")
+  attr(x, "sf_column") <- "geometry"
+  names(x)[which(names(x) == geom_name_x)] <- "geometry"
+
+  geom_name_y <- attr(y, "sf_column")
+  attr(y, "sf_column") <- "geometry"
+  names(y)[which(names(y) == geom_name_y)] <- "geometry"
+
+  if (length(id_x) != 1 | length(id_y) != 1)
+    stop("x and y must have one and only one non-geometry column")
+
+  names(x)[names(x) == id_x] <- "varx"
+  names(y)[names(y) == id_y] <- "vary"
+
+  int <- areal::aw_intersect(y,
+                             source = x,
+                             areaVar = "area")
+  int <- areal::aw_total(int, source = x,
+                         id = "varx",
+                         areaVar = "area",
+                         totalVar = "totalArea",
+                         type = "extensive",
+                         weight = "total")
+  int <- areal::aw_weight(int, areaVar = "area",
+                          totalVar = "totalArea",
+                          areaWeight = "areaWeight")
+
+  int <- right_join(st_set_geometry(int, NULL), st_set_geometry(x, NULL), by = "varx")
+
+  int <- select(int, varx, vary, w = areaWeight)
+
+  names(int) <- c(id_x, id_y, "w")
+
+  return(dplyr::as_tibble(int))
+}
+
+varx <- vary <- w <- d <- poly_id <- areaWeight <- NULL

man/calculate_area_intersection_weights.Rd

+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/calculate_area_intersection_weights.R
+\name{calculate_area_intersection_weights}
+\alias{calculate_area_intersection_weights}
+\title{Area Weighted Intersection (areal implementation)}
+\usage{
+calculate_area_intersection_weights(x, y, allow_lonlat = FALSE)
+}
+\arguments{
+\item{x}{sf data.frame source features including one geometry column and one identifier column}
+
+\item{y}{sf data.frame target features including one geometry column and one identifier column}
+
+\item{allow_lonlat}{boolean If FALSE (the default) lon/lat target features are not allowed.
+Intersections in lon/lat are generally not valid and problematic at the international date line.}
+}
+\value{
+data.frame containing fraction of each feature in x that is
+covered by each feature in y. e.g. If a feature from x is entirely within a feature in y,
+w will be 1. If a feature from x is 50% in one feature for y and 50% in another, there
+will be two rows, one for each x/y pair of features with w = 0.5 in each.
+}
+\description{
+Returns the fractional percent of each
+feature in x that is covered by each intersecting feature
+in y. These can be used as the weights in an area-weighted
+mean overlay analysis where x is the data source and area-
+weighted means are being generated for the target, y.
+
+This function is a lightwieght wrapper around the functions
+\link[areal]{aw_intersect} \link[areal]{aw_total} and \link[areal]{aw_weight}
+from the \href{https://github.com/slu-openGIS/areal}{areal package}.
+}
+\examples{
+b1 = sf::st_polygon(list(rbind(c(-1,-1), c(1,-1),
+                           c(1,1), c(-1,1),
+                           c(-1,-1))))
+b2 = b1 + 2
+b3 = b1 + c(-0.2, 2)
+b4 = b1 + c(2.2, 0)
+b = sf::st_sfc(b1, b2, b3, b4)
+a1 = b1 * 0.8
+a2 = a1 + c(1, 2)
+a3 = a1 + c(-1, 2)
+a = sf::st_sfc(a1,a2,a3)
+plot(b, border = 'red')
+plot(a, border = 'green', add = TRUE)
+
+sf::st_crs(b) <- sf::st_crs(a) <- sf::st_crs(5070)
+
+b <- sf::st_sf(b, data.frame(idb = c(1, 2, 3, 4)))
+a <- sf::st_sf(a, data.frame(ida = c(1, 2, 3)))
+
+sf::st_agr(a) <- sf::st_agr(b) <- "constant"
+
+a_b <- calculate_area_intersection_weights(a, b)
+b_a <- calculate_area_intersection_weights(b, a)
+
+}

tests/testthat/test_area_weighted.R

+context("calculate_area_intersection_weights")
+
+test_that("area_intersection", {
+
+  b1 <- sf::st_polygon(list(rbind(c(-1, -1), c(1, -1),
+                             c(1, 1), c(-1, 1),
+                             c(-1, -1))))
+  b2 <- b1 + 2
+  b3 <- b1 + c(-0.2, 2)
+  b4 <- b1 + c(2.2, 0)
+  b <- sf::st_sfc(b1, b2, b3, b4)
+  a1 <- b1 * 0.8
+  a2 <- a1 + c(1, 2)
+  a3 <- a1 + c(-1, 2)
+  a <- sf::st_sfc(a1, a2, a3)
+
+  sf::st_crs(b) <- sf::st_crs(a) <- sf::st_crs(5070)
+
+  b <- sf::st_sf(b, data.frame(idb = c(1, 2, 3, 4)))
+  a <- sf::st_sf(a, data.frame(ida = c(1, 2, 3)))
+
+  sf::st_agr(a) <- sf::st_agr(b) <- "constant"
+
+  a_b <- calculate_area_intersection_weights(a, b)
+  b_a <- calculate_area_intersection_weights(b, a)
+
+  expect_equal(as.numeric(a_b[1, ]),
+               c(1, 1, 1), info = "a1 is 100% covered by b1.")
+  expect_equal(as.numeric(a_b[2, ]),
+               c(2, 2, 0.5), info = "a2 is 50% covered by b2.")
+  expect_equal(as.numeric(a_b[3, ]),
+               c(2, 3, 0.375), info = "a2 is 37.5% covered by b3.")
+  expect_equal(as.numeric(a_b[4, ]),
+               c(3, 3, 0.625), info = "a3 is 62.5% covered by b3.")
+
+  expect_equal(as.numeric(b_a[1, ]),
+               c(1, 1, 0.64), info = "b1 is 64% covered by a1")
+  expect_equal(as.numeric(b_a[2, ]),
+               c(2, 2, 0.32), info = "b2 is 32% covered by a2")
+  expect_equal(as.numeric(b_a[3, ]),
+               c(3, 2, 0.24), info = "b3 is 24% covered by a2")
+  expect_equal(as.numeric(b_a[4, ]),
+               c(3, 3, 0.4), info = "b3 is 40% covered by a3")
+  expect_equal(data.frame(b_a[5, ]),
+               data.frame(tibble::tibble(idb = 4,
+                                 ida = as.numeric(NA),
+                                 w = as.numeric(NA))),
+               info = "b4 is not covered")
+})