/
mp_get_segments.R
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mp_get_segments.R
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#' Extract *route segments* from a Google Maps Directions API response
#' @param doc XML document with Google Maps Directions API response
#' @return Line layer (class \code{sf}) representing route segments
#' @export
#' @examples
#'
#' library(xml2)
#'
#' doc = as_xml_document(response_directions_driving)
#' seg = mp_get_segments(doc)
#' plot(seg)
#'
#' doc = as_xml_document(response_directions_transit)
#' seg = mp_get_segments(doc)
#' plot(seg)
#'
#' \dontrun{
#'
#' # Text file with API key
#' key = readLines("~/key")
#'
#' # Transit example
#' doc = mp_directions(
#' origin = c(34.81127, 31.89277),
#' destination = c(34.781107, 32.085003),
#' mode = "transit",
#' alternatives = TRUE,
#' key = key
#' )
#' seg = mp_get_segments(doc)
#' plot(seg)
#'
#' # Using waypoints
#' doc = mp_directions(
#' origin = c(34.81127, 31.89277),
#' waypoints = rbind(c(35.01582, 31.90020), c(34.84246, 31.85356)),
#' destination = c(34.781107, 32.085003),
#' alternatives = TRUE,
#' key = key
#' )
#' seg = mp_get_segments(doc)
#' plot(seg)
#'
#' }
mp_get_segments = function(doc) {
# Check status
status = doc |>
xml2::xml_find_all("/DirectionsResponse/status") |>
xml2::xml_text()
if(status != "OK") stop(sprintf("Google Maps API status is %s", status)) else {
# Count alternative routes
alternatives =
doc |>
xml2::xml_find_all("/DirectionsResponse/route") |>
length()
routes = list()
for(i in 1:alternatives) {
summary =
doc |>
xml2::xml_find_all(sprintf("/DirectionsResponse/route[%s]/summary", i)) |>
xml2::xml_text()
# Count legs
legs =
doc |>
xml2::xml_find_all(sprintf("/DirectionsResponse/route[%s]/leg", i)) |>
length()
for(l in 1:legs) {
# Count steps per alternative per leg
steps =
doc |>
xml2::xml_find_all(sprintf("/DirectionsResponse/route[%s]/leg[%s]/step", i, l)) |>
length()
for(j in 1:steps) {
travel_mode =
doc |>
xml2::xml_find_all(sprintf(
"/DirectionsResponse/route[%s]/leg[%s]/step[%s]/travel_mode"
, i, l, j)) |>
xml2::xml_text() |>
tolower()
step =
doc |>
xml2::xml_find_all(sprintf(
"/DirectionsResponse/route[%s]/leg[%s]/step[%s]/polyline/points",
i, l, j)) |>
xml2::xml_text()
instructions =
doc |>
xml2::xml_find_all(sprintf(
"/DirectionsResponse/route[%s]/leg[%s]/step[%s]/html_instructions"
, i, l, j)) |>
xml2::xml_text()
# Duration
distance_m =
doc |>
xml2::xml_find_all(sprintf(
"/DirectionsResponse/route[%s]/leg[%s]/step[%s]/distance/value"
, i, l, j)) |>
xml2::xml_text() |>
as.numeric()
distance_text =
doc |>
xml2::xml_find_all(sprintf(
"/DirectionsResponse/route[%s]/leg[%s]/step[%s]/distance/text"
, i, l, j)) |>
xml2::xml_text()
duration_s =
doc |>
xml2::xml_find_all(sprintf(
"/DirectionsResponse/route[%s]/leg[%s]/step[%s]/duration/value"
, i, l, j)) |>
xml2::xml_text() |>
as.numeric()
duration_text =
doc |>
xml2::xml_find_all(sprintf(
"/DirectionsResponse/route[%s]/leg[%s]/step[%s]/duration/text"
, i, l, j)) |>
xml2::xml_text()
# Departure & arrival time
departure_time =
doc |>
xml2::xml_find_all(sprintf(
"/DirectionsResponse/route[%s]/leg[%s]/step[%s]/transit_details/departure_time/value",
i, l, j)) |>
xml2::xml_text()
if(length(departure_time) == 0) {
departure_time = as.POSIXct(NA)} else {
departure_time = as.numeric(departure_time)
departure_time = as.POSIXct(departure_time, tz = "UTC", origin = as.POSIXct("1970-01-01 00:00:00", tz = "UTC"))
time_zone =
doc |>
xml2::xml_find_all(sprintf(
"/DirectionsResponse/route[%s]/leg[%s]/step[%s]/transit_details/departure_time/time_zone",
i, l, j)) |>
xml2::xml_text()
departure_time = format(departure_time, tz = time_zone)
departure_time = as.POSIXct(departure_time, tz = time_zone)
}
arrival_time =
doc |>
xml2::xml_find_all(sprintf(
"/DirectionsResponse/route[%s]/leg[%s]/step[%s]/transit_details/arrival_time/value",
i, l, j)) |>
xml2::xml_text()
if(length(arrival_time) == 0) {
arrival_time = as.POSIXct(NA)} else {
arrival_time = as.numeric(arrival_time)
arrival_time = as.POSIXct(arrival_time, tz = "UTC", origin = as.POSIXct("1970-01-01 00:00:00", tz = "UTC"))
time_zone =
doc |>
xml2::xml_find_all(sprintf(
"/DirectionsResponse/route[%s]/leg[%s]/step[%s]/transit_details/arrival_time/time_zone",
i, l, j)) |>
xml2::xml_text()
arrival_time = format(arrival_time, tz = time_zone)
arrival_time = as.POSIXct(arrival_time, tz = time_zone)
}
rt = decode_line(step)
rt = sf::st_linestring(rt)
rt = sf::st_sfc(rt, crs = 4326)
routes[[paste(i, l, j, sep = "-")]] = sf::st_sf(
alternative_id = i,
leg_id = l,
segment_id = j,
summary = summary,
travel_mode = travel_mode,
instructions = instructions,
distance_m = distance_m,
distance_text = distance_text,
duration_s = duration_s,
duration_text = duration_text,
departure_time = departure_time,
arrival_time = arrival_time,
geometry = rt,
stringsAsFactors = FALSE
)
}
}
}
routes = do.call(rbind, routes)
return(routes)
}
}