R/extract_coords.R

In stppSim: Spatiotemporal Point Patterns Simulation

#' @title Coordinates extraction
#' @description Extracts the bounding (edges) coordinates
#' of a polygon object.
#' @param poly (An sf or S4 object)
#' A polygon shapefile.
#' @usage extract_coords(poly)
#' @examples
#' #load boundary of Camden
#' load(file = system.file("extdata", "camden.rda",
#' package="stppSim"))
#' boundary = camden$boundary # get boundary
#' extract_coords(poly=boundary)
#' @details Given a spatial polygon object,
#' the function extracts its bounding coordinates.
#' @return Returns 2-column xy coordinates
#' representing points of directional
#' change along the boundary.
#' @importFrom magrittr %>%
#' @importFrom sf st_as_sf st_coordinates
#' @importFrom dplyr select
#' @export

extract_coords <- function(poly){

  X <- Y <- as <- asNULL <- NULL

    # #check the geometry of the input
    # if(!class(poly)[1] %in% c("SpatialPolygonsDataFrame",
    #                          "SpatialPolygons", "sf")){
    #   stop(paste("Not the required object class!"))
    # }

  #convert to as_spatial and retain the crs
  if(class(poly)[1] == "sf"){
    poly <- as(poly, 'Spatial') #convert#poly<- nc
  }

  #convert object class to simple feature (sf)
  poly2 <- st_as_sf(poly)
  poly2 <- data.frame(st_coordinates(poly2))
  poly2 <- poly2 %>%
    select(X, Y)

  return(poly2)
}