Drawing journey path using leaflet in R

Question

I am creating a Shiny dashboard with a dataframe of start longitude/latitude and end longitude/latitude cooridnated that I have plotted in R using the leaflet package:

`m=leaflet()%>%
      addTiles() %>%
      addMarkers(lng=(data$Start_long[i:j]), lat=(data$Start_lat[i:j]),popup="Start") %>%
      addCircleMarkers(lng=(data$End_long[i:j]), lat=(data$End_lat[i:j]),popup="End",clusterOptions=markerClusterOptions())`

I was wondering if there was a way to join the start and end coordinated by public transport routes (maybe through google maps API or in-library functions or failing that, join the coordinates by a straight line?

Answer 1

You can use my googleway package to both get the directions/routes, and plot it on a Google map

To use Google's API you need a valid key for each API you want to use. In this case you'll want a directions key, and for plotting the map you'll want a maps javascript key

(You can generate one key and enable it for both APIs if you wish)

To call the Directions API and plot it in R, you can do

library(googleway)

api_key <- "your_directions_api_key"
map_key <- "your_maps_api_key"

## set up a data.frame of locations
## can also use 'lat/lon' coordinates as the origin/destination
df_locations <- data.frame(
  origin = c("Melbourne, Australia", "Sydney, Australia")
  , destination = c("Sydney, Australia", "Brisbane, Australia")
  , stringsAsFactors = F
)

## loop over each pair of locations, and extract the polyline from the result
lst_directions <- apply(df_locations, 1, function(x){
  res <- google_directions(
    key = api_key
    , origin = x[['origin']]
    , destination = x[['destination']]
  )

  df_result <- data.frame(
    origin = x[['origin']]
    , destination = x[['destination']]
    , route = res$routes$overview_polyline$points
  )
  return(df_result)
})

## convert the results to a data.frame
df_directions <- do.call(rbind, lst_directions)

## plot the map
google_map(key = map_key ) %>%
  add_polylines(data = df_directions, polyline = "route")

---

And similarly in a Shiny app

library(shiny)
library(shinydashboard)
library(googleway)

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(),
  dashboardBody(
    textInput(inputId = "origin", label = "Origin"),
    textInput(inputId = "destination", label = "Destination"),
    actionButton(inputId = "getRoute", label = "Get Rotue"),
    google_mapOutput("myMap")
  )
)

server <- function(input, output){

  api_key <- "your_directions_api_key"
  map_key <- "your_maps_api_key"

  df_route <- eventReactive(input$getRoute,{

    print("getting route")

    o <- input$origin
    d <- input$destination

    return(data.frame(origin = o, destination = d, stringsAsFactors = F))
  })


  output$myMap <- renderGoogle_map({

    df <- df_route()
    print(df)
    if(df$origin == "" | df$destination == "")
      return()

    res <- google_directions(
      key = api_key
      , origin = df$origin
      , destination = df$destination
    )

    df_route <- data.frame(route = res$routes$overview_polyline$points)

    google_map(key = map_key ) %>%
      add_polylines(data = df_route, polyline = "route")
  })
}

shinyApp(ui, server)

Answer 2

You can addPolylines() to the map.

It takes two vectors as arguments, one for the lat and one for the lng, where each row is a 'waypoint'.
It's difficult to help you without knowing the structure of your data. MRE:

library(leaflet)
cities <- read.csv(textConnection("
City,Lat,Long,Pop
Boston,42.3601,-71.0589,645966
Hartford,41.7627,-72.6743,125017
New York City,40.7127,-74.0059,8406000
Philadelphia,39.9500,-75.1667,1553000
Pittsburgh,40.4397,-79.9764,305841
Providence,41.8236,-71.4222,177994
"))

leaflet() %>% 
    addTiles() %>% 
    addPolylines(lat = cities$Lat, lng = cities$Long)