R/as_wkt.R

In mregions: Marine Regions Data from 'Marineregions.org'

#' Convert data to WKT
#'
#' @export
#' @param x Output from [mr_geojson()], [mr_shp()],
#' or a `SpatialPolygonsDataFrame`
#' @param fmt (integer) The number of digits to display after the decimal
#' point when formatting coordinates. Ignored when shp files or
#' `SpatialPolygonsDataFrame` passed in
#' @param ... Further args passed on to [jsonlite::fromJSON()] only
#' in the event of json passed as a character string. Ignored when shp files or
#' `SpatialPolygonsDataFrame` passed in
#'
#' @details WKT, or Well Known Text, is a way to encode spatial data. It's
#' somewhat similar to GeoJSON, but instead of being in JSON format, it's a
#' character string (though can also be encoded in binary format). WKT is
#' often used in SQL databases, and many species occurrence APIs allow only
#' WKT. You could do the conversion to WKT yourself, but we provide
#' `as_wkt` as a convenience
#'
#' @return a character string of WKT data
#'
#' @examples \dontrun{
#' res <- mr_geojson(key = "Morocco:dam")
#' mr_as_wkt(res)
#'
#' # shp files
#' ## path to wkt
#' mr_as_wkt(mr_shp(key = "Morocco:dam", read = FALSE))
#'
#' ## spatial object to wkt
#' mr_as_wkt(mr_shp(key = "Morocco:dam", read = TRUE))
#' }
mr_as_wkt <- function(x, fmt = 16, ...) {
  UseMethod("mr_as_wkt")
}

#' @export
mr_as_wkt.default <- function(x, fmt = 16, ...) {
  stop("no 'mr_as_wkt' method for ", class(x), call. = FALSE)
}

#' @export
mr_as_wkt.mr_geojson <- function(x, fmt = 16, ...) {
  out <- geojsonio::as.json(unclass(x))
  out <- geojson::as.geojson(out)
  out <- geojsonsf::geojson_wkt(out)

  unlist(out$geometry)
}

#' @export
#' @importFrom sp spTransform
mr_as_wkt.SpatialPolygonsDataFrame <- function(x, fmt = 16, ...) {
  check4pkg("rgdal")
  check4pkg("rgeos")
  shp <- .ensureIsLonlat(x)
  rgeos::writeWKT(shp)
}

#' @export
mr_as_wkt.mr_shp_file <- function(x, fmt = 16, ...) {
  check4pkg("rgdal")
  check4pkg("rgeos")
  rgeos::writeWKT(read_shp(x))
}

.ensureIsLonlat <- function(x) {
  check <- .isLonLat(x)
  if (is.na(check)) return(x)  ## do nothing, we don't know
  if (!check) {
    ## won't work on Linux with EPSG . . .
    # x <- sp::spTransform(x, "+init=EPSG:4326")
    x <- sp::spTransform(
      x = x,
      CRSobj = " +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0"
    )
  }
  x
}

# stolen from raster::isLonLat
.isLonLat <- function(x) {
  p4 <-  x@proj4string@projargs
  if (is.na(p4)) {
    return(NA)
  }
  test <- grepl("longlat", p4, fixed = TRUE) | grepl("lonlat", p4, fixed = TRUE)
  test
}