Decode polylines obtained from Google Maps

CreateRoutes.R

library(maptools)
library(maps)
library(mapdata)
library(rjson)
library(stringr)
library(RCurl)
library(ggplot2)


GetDirections <- function(from, to) {
  Sys.sleep(1) #let's be nice internet citizens and wait 1s
  baseurl <- "http://maps.google.com/maps/nav?output=js&q=from:"
  url <- str_c(baseurl, curlEscape(str_c(
                                         str_c(" ", from),
                                         str_c(" to: ", to, collapse = " ")
                                         )))
  fromJSON(paste(readLines(url), collapse=""))
}

#Google polyline decoder borrowed from:
#http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/decode.js
DecodeLineR <- function(encoded) {
  len = str_length(encoded)
  encoded <- strsplit(encoded, NULL)[[1]]
  index = 1
  N <- 100000
  df.index <- 1
  array = matrix(nrow = N, ncol = 2)
  lat = 0
  dlat = 0
  lng = 0
  dlng = 0
  b = 0
  shift = 0
  result = 0

  while(index <= len) {
    shift = 0
    result = 0
    
    repeat {
      b = as.integer(charToRaw(encoded[index])) - 63
      index <- index + 1
      result = bitOr(result, bitShiftL(bitAnd(b, 0x1f), shift))
      shift = shift + 5
      if(b < 0x20) break
    }
    dlat = ifelse(bitAnd(result, 1),
                 -(result - (bitShiftR(result, 1))),
                 bitShiftR(result, 1))
    lat = lat + dlat;
    
    shift = 0
    result = 0
    b = 0
    repeat {
      b = as.integer(charToRaw(encoded[index])) - 63
      index <- index + 1
      result = bitOr(result, bitShiftL(bitAnd(b, 0x1f), shift))
      shift = shift + 5
      if(b < 0x20) break
    }
    dlng = ifelse(bitAnd(result, 1),
                  -(result - (bitShiftR(result, 1))),
                  bitShiftR(result, 1))
    lng = lng + dlng

    array[df.index,] <- c(lat = lat * 1e-05, lng = lng * 1e-5)
    df.index <- df.index + 1
  }
  
  ret <- data.frame(array[1:df.index - 1,])
  names(ret) <- c("lat", "lng")
  return(ret)
}

src <- '
  std::string encoded = as<std::string>(a);

  int index = 0;
  int len = encoded.size();
  int df_index = 0;
  long double lat = 0;
  long double lng = 0;
  std::vector<long double> longitude(0);
  std::vector<long double> latitude(0);

  if(encoded.size() == 0)
    return R_NilValue;

  longitude.reserve(30000);
  latitude.reserve(30000);

  while(index < len) {
   int b;
   int shift = 0;
   int result = 0;
   
   do {
     b = encoded[index++] - 63;
     result |= (b & 0x1f) << shift;
     shift += 5;
   } while(b >= 0x20);
   long double dlat = ((result & 1) ? ~(result >> 1) : (result >> 1));
   lat += dlat;
   latitude.push_back(lat * 1e-5);

   shift = 0;
   result = 0;
   do {
     b = encoded[index++] - 63;
     result |= (b & 0x1f) << shift;
     shift += 5;
   } while(b >= 0x20);
   long double dlng = ((result & 1) ? ~(result >> 1) : (result >> 1));
   lng += dlng;
   longitude.push_back(lng * 1e-5);
   df_index++;
 }

 return DataFrame::create( _["lat"] = latitude,  _["lng"] = longitude );
'
  

if (require("Rcpp") & require("inline")){
  DecodeLine <- cxxfunction(signature(a = "character"),
                   src, plugin = "Rcpp")
} else {
  DecodeLine <- DecodeLineR
}

#http://code.google.com/apis/maps/documentation/utilities/polylinealgorithm.html
poly.official <- data.frame(lat = c(38.5, 40.7, 43.252),
                   lng = c(-120.2, -120.95, -126.453))
	
all.equal(DecodeLine("_p~iF~ps|U_ulLnnqC_mqNvxq`@"),
          poly.official)
all.equal(DecodeLineR("_p~iF~ps|U_ulLnnqC_mqNvxq`@"),
          poly.official)

identical(DecodeLine("_p~iF~ps|U_ulLnnqC_mqNvxq`@"),
          DecodeLineR("_p~iF~ps|U_ulLnnqC_mqNvxq`@"))



library(compiler)
DecodeLineRC <- cmpfun(DecodeLineR)

library(rbenchmark)

benchmark(DecodeLine("_p~iF~ps|U_ulLnnqC_mqNvxq`@"),
          DecodeLineR("_p~iF~ps|U_ulLnnqC_mqNvxq`@"),
          DecodeLineRC("_p~iF~ps|U_ulLnnqC_mqNvxq`@"),
          columns=c("test", "replications", "elapsed", "relative"),
          order="relative", replications=1000)


#from Acapulco to Reynosa
dir <- GetDirections(from = "Acapulco, Mexico",
                     to = c("Mexico city, Mexico",
                            "Juarez, Chihuahua, Mexico"))
dir$Directions$Duration$html
dir$Directions$Distance$meters

#Converting the encoded polyline to a data.frame takes a really long time
system.time(dir$Decodedline <- DecodeLine(dir$Directions$Polyline$points))
#The R version is slow
system.time(dir$Decodedline <- DecodeLineR(dir$Directions$Polyline$points))

#Draw a map with the optimal highway
mexico <- data.frame(map("worldHires", "mexico", plot=FALSE)[c("x","y")])
mexico.map <- qplot(x, y, data=mexico, geom="path") + coord_map()
mexico.map + geom_path(data = dir$Decodedline, aes(lng, lat))

Hi. This doesn't seem to work. I get the message:

Error in rename(x, .base_to_ggplot, warn_missing = FALSE) :
could not find function "revalue"