R/ox_read.R

In stragu/osmexport: Import, prepare and render 'OpenStreetMap' XML files

#' Read OSM data
#'
#' Read OSM XML files, sometimes obtained from the "Export" page on
#' openstreetmap.org. Internally, uses the \code{sf::st_read()} function, which
#' itself use GDAL's OSM driver: \url{https://gdal.org/drivers/vector/osm.html}
#'
#' @param path Path to .osm file (string)
#' @param expand_tags Should the "other_tags" column be expanded into
#'   single-tag columns? (logical; default is TRUE)
#'
#' @return An object of class "osm". There are \code{print} and \code{plot}
#'   methods for this class.
#'
#'   According to GDAL, the object is made of:
#'   \itemize{
#'   \item points: “node” features that have
#'   significant tags attached
#'   \item lines: “way” features that are not recognised
#'   as areas
#'   \item multilinestrings: “relation” features that form a
#'   multilinestring (type = ‘multilinestring’ or type = ‘route’)
#'   \item
#'   multipolygons: “relation” features that form a multipolygon (type =
#'   ‘multipolygon’ or type = ‘boundary’), and “way” features that are
#'   recognised as areas
#'   \item other_relations: “relation” features that do not
#'   belong to either multilinestrings or multipolygons
#'   }
#'
#' @importFrom sf st_read st_layers st_geometry_type
#' @importFrom magrittr %>%
#' @export
#'
#' @examples
#' # read example South Brisbane .osm file
#' sb <- ox_read(
#'   system.file("extdata/south_brisbane.osm",
#'               package = "osmxml"),
#'   expand_tags = FALSE)
ox_read <- function(path, expand_tags = TRUE) {
  if (!file.exists(path)) stop("'path' is not a valid path to a .osm file")
  # store names of all components of OSM file
  layer_names <- st_layers(path)$name
  # read all layers, keeping names
  osm_layers <- sapply(layer_names, function(x) st_read(path,
                                                        layer = x,
                                                        quiet = TRUE),
                       USE.NAMES = TRUE)
  # only expand other_tags if user chose to
  if (expand_tags) {
    osm_layers <- lapply(osm_layers, ox_separate_tags)
  }
  # assign S3 class
  class(osm_layers) <- "osm"
  # return a list of class "osm"
  osm_layers
}


#' Print method for OSM objects
#'
#' @param x Object of class "osm"
#' @param ... Other arguments passed on to \link{print}
#'
#' @return Description of object: what it is and what it contains.
#' @export
#'
#' @examples
#' ox_read(
#'   system.file("extdata/south_brisbane.osm",
#'               package = "osmxml"),
#'   expand_tags = FALSE) |>
#'   print()
print.osm <- function(x, ...) {
  cat("OSM data object made of", length(x), "simple feature collections: ")
  cat(paste(names(x), collapse = ", "))
  cat("\nThe corresponding sf geometry types are:\n")
  geom_types <- sapply(x, sf::st_geometry_type, by_geometry = FALSE) %>%
    as.character()
  names(geom_types) <- names(x)
  print(geom_types, quote = FALSE, ...)
}