transpordiTsoonid/R/area2SpatialPolygonsDataFrame.R

#' Add polygon area value to Spdf
#' @details Polügooni pindala (ruutmeetrites) lisamine SpatialPolygonsDataFrame objektile. Andmetele lisatakse veerg "area".
#' @param spdf object with class "SpatialPolygonsDataFrame".
#' @return area Polygon area value in square meters.
#' @seealso \code{\link{isObjectSpatialPolygonsDataFrame}}, \code{\link{centroid2SpatialPolygonsDataFrame}},
#' \code{\link{projection2WGS84}}, \code{\link{area2SpatialPolygonsDataFrame}},
#' \code{\link{perimeter2SpatialPolygonsDataFrame}}, \code{\link{spPolygonsOutline}}
#' @examples \dontrun{
#' load(rahvaarv)
#' rahvaarv <- area2SpatialPolygonsDataFrame(spdf = rahvaarv)
#' rahvaarv@data$area
#'
#' }
#'
#' @export
#'

area2SpatialPolygonsDataFrame <- function(spdf) {
  isObjectSpatialPolygonsDataFrame(spdf)
  # Area
  # spdf@data$area <- sapply(slot(spdf, "polygons"), function(x) sapply(slot(x, "Polygons"), slot, "area"))
  spdf@data$area <- geosphere::areaPolygon(spdf)
  return(spdf)
}