add spherical options for st_sample.bbox(); #2283

Author: edzer

NAMESPACE

@@ -287,6 +287,7 @@ S3method(st_read,default)
 S3method(st_reverse,sf)
 S3method(st_reverse,sfc)
 S3method(st_reverse,sfg)
+S3method(st_sample,bbox)
 S3method(st_sample,sf)
 S3method(st_sample,sfc)
 S3method(st_sample,sfg)

NEWS.md

@@ -1,5 +1,7 @@
 # version 1.0-15
 
+* add `st_sample()` method for `bbox`, with special provisions for ellipsoidal coordinates; #2283
+
 * documentation clean-up by @olivroy; #2266, #2285
 
 * `st_convex_hull()` uses `s2::s2_convex_hull()` for geodetic coordinates; #2250

R/sample.R

@@ -141,15 +141,27 @@ st_sample.sfg = function(x, size, ...) {
 
 #' @export
 #' @name st_sample
+#' @param great_circles logical; if `TRUE`, great circle arcs are used to connect the bounding box vertices, if `FALSE` parallels (graticules)
+#' @param segments units, or numeric (degrees); segment sizes for segmenting a bounding box polygon if `great_circles` is `FALSE`
 #' @examples
 #' bbox = st_bbox(
-#'	c(xmin = 16.1, xmax = 16.6, ymax = 48.6, ymin = 47.9),
-#' 	crs = st_crs(4326)
+#'	c(xmin = 0, xmax = 40, ymax = 70, ymin = 60),
+#' 	crs = st_crs('OGC:CRS84')
 #' )
-#' 
-#' st_sample(bbox, 5)
-st_sample.bbox = function(x, size, ...) {
-	st_sample(st_as_sfc(x), size, ...)
+#' set.seed(13531)
+#' s1 = st_sample(bbox, 400)
+#' st_bbox(s1) # within bbox
+#' s2 = st_sample(bbox, 400, great_circles = TRUE)
+#' st_bbox(s2) # outside bbox
+st_sample.bbox = function(x, size, ..., great_circles = FALSE, segments = units::set_units(2, degrees)) {
+	polygon = st_as_sfc(x)
+	crs = st_crs(x)
+	if (isTRUE(st_is_longlat(x)) && !great_circles) {
+		st_crs(polygon) = NA_crs_ # to fool segmentize that we're on R2:
+		segments = units::drop_units(units::set_units(segments, degrees))
+		polygon = st_set_crs(st_segmentize(polygon, segments), crs)
+	}
+	st_sample(polygon, size, ...)
 }
 
 st_poly_sample = function(x, size, ..., type = "random",