R/kml_read.R

In briatte/tidykml: Turn KML Files Into Tidy Data Frames

#' Read a KML file.
#' 
#' @param x A string, a connection, or a raw vector.
#' All inputs accepted by \link[xml2:read_xml]{read_xml} are also accepted, as 
#' long as they are valid KML. This means that URLs and local compressed files,
#' such as \code{.zip} files, are also supported. 
#' 
#' If the source is a local file with a name ending in \code{.kmz}, 
#' \code{kml_read} will treat it as a zipped KML file and will try to read its
#' first file, as listed by \link[utils:unzip]{unzip}.
#' 
#' If the source is a link to Google My Maps, \code{kml_read} will try to 
#' download the most recent version of the map and will then treat it as a 
#' \code{.kmz} file.
#' @param ... Arguments passed to \link[xml2:read_xml]{read_xml}, such as 
#' \code{encoding} or \code{base_url}.
#' See \link[xml2:read_xml]{read_xml} for details.
#' @return A nodeset.
#' @examples
#' # demo data: U.S. Civil War map
#' # see ?states for details
#' f <- system.file("extdata", "states.kml.zip", package = "tidykml")
#' kml_read(f)
#' @seealso Google Developers. KML Reference.
#' \url{https://developers.google.com/kml/documentation/kmlreference}
#' @importFrom stringr %>% str_detect str_extract
#' @importFrom utils unzip
#' @importFrom xml2 read_xml xml_ns
#' @export
kml_read <- function(x, ...) {
  
  if (is.character(x) &&
      str_detect(x, "^https?://(www\\.)?google\\.com/maps/d/(embed|viewer)")) {
    
    # case: live KML file from Google My Maps
    
    f <- tempfile(fileext = ".kmz")
    x <- str_c("https://google.com/maps/d/kml?",
               str_extract(x, "mid=(_|-|\\w)+"))
    
    message("KMZ: ", x)
    
    httr::GET(x) %>%
      httr::content("raw") %>%
      writeBin(f)

    x <- kml_read(f)
    unlink(f) # be clean
    
    return(x)
    
  } else if (is.character(x) && file.exists(x) && str_detect(x, "\\.kmz$")) {
    # case: local KMZ file
  
    y <- unzip(x, list = TRUE)[1, 1]
    message("KML: ", y)
    
    x <- read_xml(unz(x, y), ...)

  } else if (is.character(x)) {
    x <- read_xml(x, ...)
  }
  
  y <- xml_ns(x)
  if (!length(y) || !str_detect(y, "/kml/")) {
    stop("Source does not seem to be a valid KML document.")
  }
  
  return(x)
  
}