R/to_sf.R

In rOpenGov/fmi2: Finnish Meteorological Institute open data API R client

#' Transform a fmi_api object into a sf object.
#'
#' FMI API response object's XML (GML) content is temporarily wrtitten on disk
#' and then immediately read back in into a sf object.
#'
#' @param api_obj fmi api object
#'
#' @return sf object
#'
#' @importFrom methods is
#' @importFrom sf st_read
#' @importFrom xml2 write_xml
#'
#' @note For internal use, not exported.
#'
#' @author Joona Lehtomäki <joona.lehtomaki@@iki.fi>
#'
#' @seealso \link[fmi2]{fmi_api}
#'
#' @examples
#'   \dontrun{
#'     response <- fmi_api(request = "getFeature",
#'                         storedquery_id = "fmi::observations::weather::daily::timevaluepair",
#'                         starttime = "2019-01-01", endtime = "2019-01-04",
#'                         fmisid = 100946)
#'     sf_obj <- to_sf(response)
#'   }
#'
to_sf <- function(api_obj) {
  if (!methods::is(api_obj, "fmi_api")) {
    stop("Object provided must be of class fmi_api, not ", class(api_obj))
  }
  # Get response content
  content <- api_obj$content
  # Write the content to disk
  destfile <- paste(tempfile(), ".gml", sep = '')
  xml2::write_xml(content, destfile)

  # Read the temporary GML file back in
  features <- sf::st_read(destfile, quiet = TRUE)

  return(features)
}