ggmap route finding - doesn't stay on roads

Question

I am trying to map a route using the route() function in ggmap. My problem is that the route doesn\'t stay on the roads. Is there something that my route_df <- route(or

Answer 1

It looks like you are not actually getting the required polylines from route() since the default output= parameter is set to simple. You probably need to change it to all as below and start decoding the polylines.

Below is one solution that is based on the decodeLine() function taken from here. Their solution is to define a custom function that decodes polylines and then plot everything it decoded.

library(ggmap)
library(leaflet)
way1txt <- "Tinsletown, Vancouver, BC"
way2txt <- "Science World, Vancouver, BC"

route_all <- route(way1txt, way2txt, structure = "route",
                   output = "all")

# Custom decode function
# Taken from http://s4rdd.blogspot.com/2012/12/google-maps-api-decoding-polylines-for.html

decodeLine <- function(encoded){
  require(bitops)

  vlen <- nchar(encoded)
  vindex <- 0
  varray <- NULL
  vlat <- 0
  vlng <- 0

  while(vindex < vlen){
    vb <- NULL
    vshift <- 0
    vresult <- 0
    repeat{
      if(vindex + 1 <= vlen){
        vindex <- vindex + 1
        vb <- as.integer(charToRaw(substr(encoded, vindex, vindex))) - 63  
      }

      vresult <- bitOr(vresult, bitShiftL(bitAnd(vb, 31), vshift))
      vshift <- vshift + 5
      if(vb < 32) break
    }

    dlat <- ifelse(
      bitAnd(vresult, 1)
      , -(bitShiftR(vresult, 1)+1)
      , bitShiftR(vresult, 1)
    )
    vlat <- vlat + dlat

    vshift <- 0
    vresult <- 0
    repeat{
      if(vindex + 1 <= vlen) {
        vindex <- vindex+1
        vb <- as.integer(charToRaw(substr(encoded, vindex, vindex))) - 63        
      }

      vresult <- bitOr(vresult, bitShiftL(bitAnd(vb, 31), vshift))
      vshift <- vshift + 5
      if(vb < 32) break
    }

    dlng <- ifelse(
      bitAnd(vresult, 1)
      , -(bitShiftR(vresult, 1)+1)
      , bitShiftR(vresult, 1)
    )
    vlng <- vlng + dlng

    varray <- rbind(varray, c(vlat * 1e-5, vlng * 1e-5))
  }
  coords <- data.frame(varray)
  names(coords) <- c("lat", "lon")
  coords
}


route_df <- decodeLine( route_all$routes[[1]]$overview_polyline$points )


# Map using Leaflet R
m = leaflet() %>% addTiles()
m = m %>% addPolylines(route_df$lon, route_df$lat, fill = FALSE)
m = m %>% addPopups(route_df$lon[1], route_df$lat[1], 'Origin')
m = m %>% addPopups(route_df$lon[length(route_df$lon)], 
                    route_df$lat[length(route_df$lon)], 'Destination')
m

And I get this:

For reference, there is another decodeLine function here written by @diegovalle.