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R: Create tibbles from Points and Polygons in a Google Maps KML file – not particularly efficient code, but should do the trick; answer to http://stackoverflow.com/q/19497652/635806
#' Read Points out of a KML file.
#'
#' @param x A KML file exported from Google Maps.
#' @param layer The name of the layer to extract from: defaults to \code{"d1"}.
#' @param verbose Whether to report invalid coordinates and/or altitudes below
#' sea level; defaults to \code{TRUE}. See \link{kml_coordinate}.
#' @return A \link[tibble:tibble]{tibble} containing the \code{name},
#' \code{description}, \code{styleUrl} and Point coordinates (\code{longitude},
#' \code{latitude} and \code{altitude}) of each Placemark element contained in
#' the KML file. Placemark elements with no Point coordinates, such as Polygon
#' elements, will be discarded.
#' @seealso \url{https://developers.google.com/kml/documentation/kmlreference}
kml_points <- function(x, layer = "d1", verbose = TRUE) {
require(dplyr)
require(stringr)
require(xml2)
#' Extract Placemark fields.
#'
#' @param x A nodeset of Placemarks.
#' @param field The name of the field to extract, e.g. \code{"name"}.
#' @param layer The name of the layer to extract from; defaults to \code{"d1"}.
#' @return A character vector. Missing values, i.e. empty fields, will be
#' returned as \code{NA} values.
get_field <- function(x, field, layer = "d1") {
# vectorization required to get missing values when field is xml_missing
lapply(x, xml_find_first, str_c(layer, ":", field)) %>%
sapply(xml_text)
}
x <- read_xml(x) %>%
xml_find_all(str_c("//", layer, ":Point/.."))
x <- data_frame(
name = get_field(x, "name", layer),
description = get_field(x, "description", layer),
styleUrl = get_field(x, "styleUrl", layer),
coordinates = get_field(x, str_c("Point/", layer, ":coordinates"), layer)
)
x$longitude <- kml_coordinate(x$coordinates, 1, verbose)
x$latitude <- kml_coordinate(x$coordinates, 2, verbose)
x$altitude <- kml_coordinate(x$coordinates, 3, verbose)
return(select(x, -coordinates))
}
#' Read Polygons out of a KML file.
#'
#' @param x A KML file exported from Google Maps.
#' @param layer The name of the layer to extract from: defaults to \code{"d1"}.
#' @param verbose Whether to report invalid coordinates and/or altitudes below
#' sea level; defaults to \code{TRUE}. See \link{kml_coordinate}.
#' @return A \link[tibble:tibble]{tibble} containing the \code{name},
#' \code{description}, \code{styleUrl} and Point coordinates (\code{longitude},
#' \code{latitude} and \code{altitude}) of each Placemark element contained in
#' the KML file. Placemark elements with no Point coordinates, such as Polygon
#' elements, will be discarded.
#' @seealso \url{https://developers.google.com/kml/documentation/kmlreference}
kml_polygons <- function(x, layer = "d1", verbose = TRUE) {
require(dplyr)
require(stringr)
require(xml2)
#' Extract Placemark fields.
#'
#' @param x A nodeset of Placemarks.
#' @param field The name of the field to extract, e.g. \code{"name"}.
#' @param layer The name of the layer to extract from; defaults to \code{"d1"}.
#' @return A character vector. Missing values, i.e. empty fields, will be
#' returned as \code{NA} values.
get_field <- function(x, field, layer = "d1") {
xml_find_first(x, str_c(layer, ":", field)) %>%
xml_text
}
x <- read_xml(x) %>%
xml_find_all(str_c("//", layer, ":Polygon/.."))
x <- lapply(x, function(x) {
data_frame(
name = get_field(x, "name"),
description = get_field(x, "description"),
styleUrl = get_field(x, "styleUrl"),
coordinates = get_field(x, str_c("Polygon//", layer, ":coordinates")) %>%
str_split(" ") %>%
unlist
)
}) %>%
bind_rows
x$longitude <- kml_coordinate(x$coordinates, 1)
x$latitude <- kml_coordinate(x$coordinates, 2)
x$altitude <- kml_coordinate(x$coordinates, 3)
return(select(x, -coordinates))
}
#' Extract KML coordinates
#'
#' @param x A character vector of KML coordinates, of the form
#' \code{"longitude,latitude,altitude"}.
#' @param coord Which coordinate to extract: either \code{1} (longitude),
#' \code{2} (latitude) or \code{3} (altitude).
#' @param verbose Whether to report invalid coordinates and/or altitudes below
#' sea level; defaults to \code{TRUE}.
#' @return A numeric vector.
#' @seealso \url{https://developers.google.com/kml/documentation/kmlreference}
kml_coordinate <- function(x, coord, verbose = TRUE) {
require(stringr) # includes `%>%`
x <- str_replace(x, "(.*),(.*),(.*)", str_c("\\", coord)) %>%
as.numeric
if (verbose && coord == 1 && any(abs(x) > 180))
message("Some longitudes are not contained within [-180, 180].")
if (verbose && coord == 2 && any(abs(x) > 90))
message("Some latitudes are not contained within [-90, 90].")
if (verbose && coord == 3 && any(x < 0))
message("Some altitudes are below sea level.")
return(x)
}
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