#' Outline for the polygons
#' @details Tsoonidele piirjoone leidmine. Funktsiooni abil leitakse kõikide polügoonide ühisosa.
#' Augud polügoonide sees eemaldatakse
#' @param spdf object with class "SpatialPolygonsDataFrame".
#' @return SpatialPolygon Object with class "SpatialPolygon".
#' @seealso \code{\link{isObjectSpatialPolygonsDataFrame}}, \code{\link{centroid2SpatialPolygonsDataFrame}},
#' \code{\link{projection2WGS84}}, \code{\link{area2SpatialPolygonsDataFrame}},
#' \code{\link{perimeter2SpatialPolygonsDataFrame}}, \code{\link{spPolygonsOutline}}
#' @examples \dontrun{
#' load(tr_tsoonid)
#' tr_tsoonid.outline <- perimeter2SpatialPolygonsDataFrame(spdf = tr_tsoonid)
#' tr_tsoonid.outline
#'
#' }
#'
#' @export
#'

spPolygonsOutline <- function(spdf) {
  # Remove intersections
  # if(!rgeos::gIsValid(spdf)) {spdf <- rgeos::gBuffer(spdf, byid=FALSE, width=.00000001)} # .000001
  # if(!rgeos::gIsValid(spdf)) {message("Remove intersections form spatial polygons."); return(NULL)}
  spdf <- rgeos::gBuffer(spdf, byid=FALSE, width=.00000001)
  outerRings = Filter(function(f){f@ringDir==1},spdf@polygons[[1]]@Polygons)
  outerBounds = sp::SpatialPolygons(list(sp::Polygons(outerRings,ID=1)))
  outerBounds@proj4string <- sp::CRS("+init=epsg:4326")
  # plot(outerBounds, col = "red", border = "green", lwd = .8)
  outerBounds
}