R/extentToVect.r

In enmSdmX: Species Distribution Modeling and Ecological Niche Modeling

#' Convert extent to a spatial polygon
#'
#' This function returns a \code{SpatVector} or \code{sf} polygon representing an extent. The input can be a \code{SpatExtent} or \code{sf} object, or an object from which a \code{SpatExtent} (extent) can be obtained.
#'
#' @param x A \code{sf}, \code{SpatVector}, \code{SpatRaster}, \code{sf}, \emph{or} a vector of four numeric values representing (in this order): x-coordinate of western side of the extent, x-coordinate of eastern side, y-coordinate of the southern side, and y-coordinate of the northern side. If numeric coordinates are supplied, the output will not have a CRS assigned to it unless supplied in \code{...}
#' @param ... Arguments to supply to \code{vect}.
#'
#' @return A \code{SpatVector} (usual) or, if the input is an \code{sf} object, an \code{sf} polygon object.
#' @seealso \link{plotExtent}
#' @examples
#'
#' data(mad0)
#' madExtent <- extentToVect(mad0)
#' plot(madExtent, border='blue', lty='dotted')
#' plot(mad0[1], add=TRUE)
#'
#' # NB This is the same as:
#' library(terra)
#' madExtent <- ext(mad0)
#' madExtent <- as.polygons(madExtent, crs = crs(mad0))
#' 
#' @export
extentToVect <- function(x, ...) {

	if (inherits(x, c('numeric'))) {

		xCorners <- c(x[1L], x[2L], x[2L], x[1L])
		yCorners <- c(x[3L], x[3L], x[4L], x[4L])
		corners <- cbind(xCorners, yCorners)
		out <- terra::vect(corners, type='polygon', ...)
		
	} else if (inherits(x, c('SpatVector', 'SpatRaster'))) {

		proj <- terra::crs(x)

		x <- as.vector(terra::ext(x))
		xCorners <- c(x[1L], x[2L], x[2L], x[1L])
		yCorners <- c(x[3L], x[3L], x[4L], x[4L])
		corners <- cbind(xCorners, yCorners)
		out <- terra::vect(corners, type='polygon', crs=proj, ...)
	
	} else if (inherits(x, 'sf')) {
	
		proj <- sf::st_crs(x)

		x <- sf::st_bbox(x)
		xCorners <- c(x['xmin'], x['xmax'], x['xmax'], x['xmin'], x['xmin'])
		yCorners <- c(x['ymin'], x['ymin'], x['ymax'], x['ymax'], x['ymin'])
		corners <- cbind(xCorners, yCorners)
		corners <- list(corners)
		out <- sf::st_polygon(corners)
		out <- sf::st_geometry(out)
		out <- sf::st_as_sf(out, crs=proj)
			
	} else {
		stop('Argument x must be a vector of 4 numbers, a SpatVector, a SpatRaster, or an sf object.')
	}
	
	out
	
}