Google Map itinerary from geoJSON file

I'd like to draw an itinerary between 2 markers which are defined in this geoJSON file:

{
"type": "FeatureCollection",
"features":

 [

    { "type": "Feature",
        "geometry": {"type": "Point", "coordinates": [-73.563032, 45.495403]},
        "properties": {"prop0": "value0"}
    },

    { "type": "Feature",
        "geometry": {"type": "Point", "coordinates": [-73.549762, 45.559673]},
        "properties": {"prop0": "value0"}
    }
]

}

The two markers are displayed well on the map.

Now I want to create an itinerary (car), between those two points.

I have this javascript function, which allows me to draw an itinerary from a form filled by the user:

function calculate() {

origin      =   document.getElementById('origin').value;
destination =   document.getElementById('destination').value;


var request = {
origin: origin,
destination: destination,


travelMode: google.maps.TravelMode.DRIVING
 };
 directionsService.route(request, function(response, status) {
 if (status == google.maps.DirectionsStatus.OK) {
  directionsDisplay.setDirections(response);
     }
   });
  }

And now, I would like to replace the "origin" and "destination", by the 2 points defined in my geoJSON file, in order to create an itinerary between those two points.

Any idea ?

Thank you for your help !

One possible solution, use the Google Maps Data Layer to display your GeoJSON. The use it to retrieve the coordinates and get directions between them. The below code assumes 2 points (and uses your example with 2 points):

working fiddle

function calculate() {
    var request = {
        origin: origin,
        destination: destination,


        travelMode: google.maps.TravelMode.DRIVING
    };
    directionsService.route(request, function (response, status) {
        if (status == google.maps.DirectionsStatus.OK) {
            directionsDisplay.setDirections(response);
        }
    });
}

// global variables
var origin = null;
var destination = null;
var infowindow = new google.maps.InfoWindow();
var directionsDisplay = new google.maps.DirectionsRenderer();
var directionsService = new google.maps.DirectionsService();

function initialize() {
    // Create a simple map.
    features = [];
    map = new google.maps.Map(document.getElementById('map-canvas'), {
        zoom: 4,
        center: {
            lat: -28,
            lng: 137.883
        }
    });
    directionsDisplay.setMap(map);
    directionsDisplay.setPanel(document.getElementById('directions-panel'));
    google.maps.event.addListener(map, 'click', function () {
        infowidow.close();
    });
    // process the loaded GeoJSON data.
    google.maps.event.addListener(map.data, 'addfeature', function (e) {
        if (e.feature.getGeometry().getType() === 'Point') {
            map.setCenter(e.feature.getGeometry().get());
            // set the origin to the first point
            if (!origin) origin = e.feature.getGeometry().get();
            // set the destination to the second point
            else if (!destination) {
                destination = e.feature.getGeometry().get();
                // calculate the directions once both origin and destination are set 
                calculate();
            }
        }
    });
    map.data.addGeoJson(data);
}

google.maps.event.addDomListener(window, 'load', initialize);