google maps API v3 : computing distance between 2 points on a polyline - google-maps-api-3

Question

I am a bit confused with my code and I don't really know which way to go.
Let's consider I have a car marker that is running through a polyline.
I change its position each 500 ms by setting a timer :
function animate() {
var p = polyline.GetPointAtDistance(distanceFromBeginning);
carMarker.setPosition(p);
distanceFromBeginning += step;
timerHandle = setTimeout("animate("+(distanceFromBeginning)+")", tick);
}
I also added the fact that my car can be dragged on the route :
google.maps.event.addDomListener(carMarker, 'dragend', function(e) {
var p = find_closest_point_on_path(e.latLng,polyline.getPath());
console.log("position is : " + p);
carMarker.setPosition(p);
console.log("dragend")
});
Now that I have a new position after dragging the car on the polyline, how can I get its distance from the start location so I can update it correctly in my timer?

Answer 1

Once you have the coordinates for the end location (lets call the "destination"), and assuming that on your 'dragend' event you set the coordinates for the car (let call "origin") location you can call this function on your listener:
function calculateDistances() {
var service = new google.maps.DistanceMatrixService();
service.getDistanceMatrix(
{
origins: [origin],
destinations: [destination],
travelMode: google.maps.TravelMode.DRIVING,
unitSystem: google.maps.UnitSystem.METRIC,
avoidHighways: false,
avoidTolls: false
}, callback);
}
function callback(response, status) {
if (status != google.maps.DistanceMatrixStatus.OK) {
alert('Error was: ' + status);
} else {
var origins = response.originAddresses;
var destinations = response.destinationAddresses;
for (var i = 0; i < origins.length; i++) {
var results = response.rows[i].elements;
for (var j = 0; j < results.length; j++) {
console.log(results[j].distance.text);
console.log(results[j].duration.text);
}
}
}
}
Check this example on jsfiddle based on the Google documentation(look the result on your console)
Fell free to reply if you need more help with this code or if it's not what you want.