R: Connecting Dots on a Map

Question

I am working with the R programming language.

Using the "leaflet" library, I made the following map for these 5 cities:

library(dplyr)
library(leaflet)

map_data <- data.frame("Lat" = c(43.6426, 43.6424, 43.6544, 43.6452, 43.6629), "Long" = c(-79.3871, -79.3860, -79.3807, -79.3806,-79.3957 ), type = c(1,2,3,4,5))

map_data$type = as.factor(map_data$type)



leaflet(map_data) %>%
    addTiles() %>% addCircleMarkers(stroke = FALSE, label = ~type,fillOpacity = 0.8, labelOptions = labelOptions(direction = "center",style = list('color' = "white"),noHide = TRUE, offset=c(0,0), fill = TRUE, opacity = 1, weight = 10, textOnly = TRUE))

On this above map that I have created, I would now like to "connect" all these "points" (i.e. cities) on the map (in a route) based on their "number" (e.g. connect 1 with 2, 2 with 3, 3 with 4, 4 with 5, 5 with 1), and output the "total distance" of the route. I found a previous post that shows how to do this: How to show path and distance on map with leaflet, shiny apps?

I tried to adapt the code from this post to suit my question:

library(osrm)

route = osrmRoute(c(-79.3871, -79.3860, -79.3807, -79.3806,-79.3957 ), c(43.6426, 43.6424, 43.6544, 43.6452, 43.6629),  overview = 'full')


route_summary = osrmRoute(c(-79.3871, -79.3860, -79.3807, -79.3806,-79.3957 ), c(43.6426, 43.6424, 43.6544, 43.6452, 43.6629), overview = FALSE)

leaflet() %>% addTiles() %>% 
    addCircleMarkers(c(-79.3871, -79.3860, -79.3807, -79.3806,-79.3957 ), c(43.6426, 43.6424, 43.6544, 43.6452, 43.6629), stroke = FALSE, label = ~type,fillOpacity = 0.8, 
                     labelOptions = labelOptions(direction = "center",style = list('color' = "white"),noHide = TRUE, offset=c(0,0), fill = TRUE, opacity = 1, weight = 10, textOnly = TRUE)) %>% 
    addPolylines(route$lon,route$lat, 
                 label = paste(round(route_summary[1]/60), 'hr - ', round(route_summary[2]), 'km'), 
                 labelOptions = labelOptions(noHide = TRUE))

But this returns the following error:

Error in UseMethod("metaData") : 
  no applicable method for 'metaData' applied to an object of class "NULL"

Can someone please show me how to fix this problem?

I would like to do this using "leaflet" and not using "rshiny". In the end, I would like the final map to look something like this (this is supposed to represent a "single path" from a Travelling Salesman Problem) :

[![enter image description here][2]][2]

Note: I am starting to think that problem might be that the "osrmRoute()" function might not be able to work for more than 2 points?

• https://github.com/riatelab/osrm/issues/41
• https://rdrr.io/cran/osrm/man/osrmTrip.html

Answer 1

One way is for you to make API call:

https://github.com/Project-OSRM/osrm-backend/blob/master/docs/http.md

I'll just outline how can you do it:

data

df <- data.frame(
  lon = c(-79.3871, -79.3860, -79.3807, -79.3806,-79.3957), 
  lat = c(43.6426, 43.6424, 43.6544, 43.6452, 43.6629)
)

url call

root <- "http://router.project-osrm.org/route/v1/driving/"

options <- c(
  continue_straight = "true",
  overview = "full",
  annotations = "true",
  steps = "true"
) 
  
coords <- df %>% 
  slice(c(seq_len(n()), 1)) %>%
  pmap_chr(str_c, sep = ",") %>% str_c(collapse = ";")
options <- options %>%
  imap_chr(~str_c(.y, "=", .x)) %>%
  str_c(collapse = "&") %>%
  str_c("?", .)

res <- rjson::fromJSON(file = str_c(root, coords, options))

Note that I've added first point as 6th row to make circle route.

map

res$routes[[1]]$geometry %>%
  googlePolylines::decode() %>%
  .[[1]] %>%
  leaflet() %>%
  addTiles() %>%
  addPolylines(lng = ~lon, lat = ~lat) %>%
  addCircleMarkers(
    data = df,
    stroke = FALSE, 
    label = seq_len(nrow(df)),
    fillOpacity = 0.8, 
    labelOptions = labelOptions(
      direction = "center",
      style = list('color' = "white"),
      noHide = TRUE, 
      offset=c(0,0), 
      fill = TRUE, 
      opacity = 1, 
      weight = 10, 
      textOnly = TRUE
    )
  )   

distance

res$routes[[1]]$distance

This is in meters (documentation)

EDIT

There probably is better way of labeling polyline but I don't have time now:

library(sf)

segment_df <- df %>% rbind(df[1,])

d <- segment_df %>%
  st_as_sf(coords = c("lon", "lat"), crs = 4326) %>%
  {st_distance(.[-6,], .[-1,], by_element = TRUE)} %>%
  as.vector() %>%
  round()

m <- leaflet() %>% addTiles()
for(i in seq_len(nrow(segment_df) - 1))
  m <- m %>% addPolylines(
    data = segment_df[i:(i+1),], 
    lng = ~lon, lat = ~lat, color = "red", label = paste(d[[i]], "m"),
    labelOptions(noHide = TRUE, direction = 'top')
  )

m <- m %>% addCircleMarkers(
    data = df,
    stroke = FALSE, 
    label = seq_len(nrow(df)),
    fillOpacity = 0.8, 
    labelOptions = labelOptions(
      direction = "center",
      style = list('color' = "white"),
      noHide = TRUE, 
      offset=c(0,0), 
      fill = TRUE, 
      opacity = 1, 
      weight = 10, 
      textOnly = TRUE
    )
  ) 

If you want only to show total distance then that is easier and does not require loop, just replace loop with:

segment_df %>%
  leaflet() %>%
  addTiles() %>%
  addPolylines(
    lng = ~lon, lat = ~lat, color = "red", 
    label = paste(sum(d), "m"),
    labelOptions = labelOptions(noHide = TRUE, direction = 'top')
  )

I hope you understand (and see from map) that this is not drivable.

Answer 2

Here is an answer I tried based on @det's answer:

library(sf)
library(geosphere)
library(dplyr)
library(leaflet)
library(data.table)
library(VPF)



#add a 6th row that is equal to the 1st row -  so that the path loops back

   map_data <- data.frame("Lat" = c(43.6426, 43.6424, 43.6544, 43.6452, 43.6629, 43.6426), "Long" = c(-79.3871, -79.3860, -79.3807, -79.3806,-79.3957, -79.3871 ), type = c(1,2,3,4,5,1))

map_data$type = as.factor(map_data$type)


m1 = leaflet(map_data) %>% addTiles() %>% addCircleMarkers(stroke = FALSE, label = ~type,fillOpacity = 0.8, 
color = ~ifelse(type==1,"red","blue"), labelOptions = labelOptions(direction = "center",style = list('color' = "white"),
noHide = TRUE, offset=c(0,0), fill = TRUE, opacity = 1, weight = 10, textOnly = TRUE))


   m1 %>% addTiles() %>%
    addPolylines(data = map_data, lng = ~Long, lat = ~Lat, group = ~type)

Now, I want to calculate the total distance of the trip and have it displayed on the map:

#distances  (https://stackoverflow.com/questions/42119438/calculate-distance-between-two-long-lat-coordinates-in-a-dataframe)

result = rbind(
  cbind(map_data[1:nrow(map_data)-1,c(1,2)], map_data[-1,c(1,2)]),
  cbind(map_data[nrow(map_data), c(1,2)], map_data[1,c(1,2)])
)
colnames(result) <- c("start_lat", "start_long", "end_lat", "end_long")

result$id = as.factor(c(1,2,3,4,5,1))

result = data.frame(result)
 
for (i in 1:nrow(result)) {
    
    a<-result$start_long[i]
    b<-result$start_lat[i]
    c<-result$end_long[i]
    d<-result$end_lat[i]
    
    result$distance[i]<-distm(c(a,b),c(c,d), fun = distHaversine)
}

#total distance of trip in meters
d = result$distance

total_d = signif(sum(d),3)

m1 %>% addPolylines(
    data = map_data, 
    lng = ~Long, lat = ~Lat, color = "blue", label = paste0(total_d, " meters"),
    labelOptions(noHide = TRUE, direction = 'top')
  )

I think I finally got it - thanks so much @ Det!