R/util-kml_to_csv.r

In ocean-tracking-network/glatos: A package for the Great Lakes Acoustic Telemetry Observation System

#' KML To CSV Conversion
#'
#' Function for extracting features (points, lines, polygons) from kml files and
#' writing them to csv files.
#'
#' @param filePath The pathname for the kml file you wish to convert.
#'
#' @param type Optional character string indicating the type(s) of feature(s)
#'   to read from the kml file. Valid values are `c("points", "lines", and
#'   "polygons")`.
#'
#' @details kmz files are not supported. Make sure exports from Google earth are
#'   saved as kml. Or extract (unzip) kml from kmz.
#'
#' @return A csv file (same name as input `filePath` but with `csv`
#'   extension) is written to directory containing input `filePath`
#'   with five columns \describe{
#'   \item{name}{Feature name}
#'   \item{feature_type}{Feature type}
#'   \item{seq}{Sequential position in feature}
#'   \item{longitude}{Longitude}
#'   \item{latitude}{Latitude}
#'   \item{altitude}{Altitude}
#'   }
#'
#' @examples
#'
#' # Get example kml with two polygons
#' kml_file <- system.file("extdata", "example_polygons.kml",
#'   package = "glatos"
#' )
#'
#' kml_to_csv(kml_file)
#'
#' @export

kml_to_csv <- function(filePath,
                       type = c("points", "lines", "polygons")) {
  # Change type to sf-style types
  type[type == "points"] <- "POINT"
  type[type == "lines"] <- "LINE"
  type[type == "polygons"] <- "POLYGON"

  # Unzip if kmz
  fileExt <- tools::file_ext(filePath)

  if (tolower(fileExt) == "kmz") stop("kmz are not supported.")

  # Read kml
  kml <- sf::read_sf(filePath, as_tibble = FALSE)

  # Get types of features in the kml file.
  fTypes <- as.character(sf::st_geometry_type(kml))

  # Subset
  kml <- kml[fTypes %in% type]
  fTypes <- fTypes[fTypes %in% type]

  # Get names of features in the kml file.
  fNames <- kml$Name

  # Preallocate list object
  fList <- vector("list", length(fNames))
  names(fList) <- fNames

  # Write kml features to csv
  for (i in 1:length(fNames)) {
    coords_i <- sf::st_coordinates(kml$geometry[i])

    fList[[i]] <- data.frame(
      name = fNames[i],
      feature_type = fTypes[i],
      seq = 1:nrow(coords_i),
      longitude = coords_i[, "X"],
      latitude = coords_i[, "Y"],
      altitude = coords_i[, "Z"],
      stringsAsFactors = FALSE
    )
  } # end i

  fDF <- do.call(rbind, fList)

  # Write
  out_file <- gsub("kml$", "csv", filePath)

  write.csv(fDF, out_file, row.names = FALSE)

  return(out_file)
}