Getting driving distance between two points (lat, lon) using R and Google Map API

Question

I am trying to get the driving distance between two points with lat/lon given. I can manually put them into google map and get the driving distance but I want to do all this pr

Answer 1

At time of writing, Renjin (a Java-based R interpreter) does not have a lot of packages to help solve this problem. Here is an implementation that does not depend on extra packages.

# Computes the distance between two locations in meters. This uses an online
# map API and therefore an Internet connection is required for an accurate
# result. If no connection is found, this will use the Haversine formula
# to provide a rough estimate for the distance.
#
# @param src The source latitude and longitude.
# @param dst The destination latitude and longitude.
# @param mode Driving, cycling, walking, etc.
distance <- function( lat1, lon1, lat2, lon2, mode = 'driving' ) {
  lat1 = as.numeric( lat1 )
  lon1 = as.numeric( lon1 )
  lat2 = as.numeric( lat2 )
  lon2 = as.numeric( lon2 )

  # Create the URL to use to get the distance data.
  url = paste0(
    'https://maps.googleapis.com/maps/api/distancematrix/xml?',
    'origins=', lat1,
    ',', lon1,
    '&destinations=', lat2,
    ',', lon2,
    '&mode=', mode,
    '&sensor=false'
  )

  tryCatch({
    # Download the XML document with distance information.
    xml = readLines( url )

    # The  element immediately follows the distance element.
    value = xml[ grep( "", xml ) + 1 ]

    # Obtain the distance in meters.
    meters = sub( ".*>(.*?)<.*", "\\1", value )

    # Return the distance.
    as.numeric( meters )
  },
  warning = function( w ) {
    haversine( lat1, lon1, lat2, lon2 )
  },
  error = function( e ) {
    haversine( lat1, lon1, lat2, lon2 )
  })
}

# Computes distance using Haversine formula.
#
# Returns the result in meters.
haversine <- function( lat1, lon1, lat2, lon2, radius = 6371 ) {
  # Convert decimal degrees to radians
  lon1 = lon1 * pi / 180
  lon2 = lon2 * pi / 180
  lat1 = lat1 * pi / 180
  lat2 = lat2 * pi / 180

  # Haversine formula
  dlon = lon2 - lon1
  dlat = lat2 - lat1
  a = sin(dlat/2)**2 + cos(lat1) * cos(lat2) * sin(dlon/2)**2
  c = 2 * atan2(sqrt(a), sqrt(1-a))

  return( radius * c * 1000 )
}

Output:

distance( '44.5646', '-123.2620', '41.2861', '-124.0902' )
[1] 495892
distance( 44.5646, -123.2620, 41.2861, -124.0902, mode='walking' )
[1] 487715

Conversion from meters to feet is an exercise for the reader.