Google-maps – How to find location along a route with Google Maps

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I've been able to use the DirectionServices portion of the Google Maps API to find a route between two addresses. Given the starting address and a distance (e.g. 5 miles), I'd like to plot the resulting point (e.g. 5 miles along the route) on the map.

Does anybody know how to accomplish this?

Best Answer

Check out http://code.google.com/apis/maps/documentation/flash/reference.html#Route

Objects of this class are created by the Directions object to store information about a single route in a directions result.

This allows you to use the getStep method. Steps provide you with distance, duration, latlng etc.

http://code.google.com/apis/maps/documentation/flash/reference.html#Step

In order to get the point at (e.g.) 5 miles, you could get the two points closest to this distance. From what I understand these points should be line of sight (i.e. point-to-point with no turns) so you should be able to extrapolate the correct point between them using math.

There seems to be a related discussion here: http://groups.google.com/group/google-maps-js-api-v3/browse_thread/thread/a475d03a28865614/23ed9e966d10cdd8?pli=1

Here is an example of an animation which shows the mileage, so I'd be surprised if you couldn't get something working by looping through the points until you've found the value you want (the source on this page should get you started): http://econym.org.uk/gmap/example_cartrip.htm

Sorry I don't have a more concrete answer - I will try and write some code for this when I have some time.

EDIT: if you look at the car_trip example, you will find the following:

// === A method which returns the Vertex number at a given distance along the path ===
// === Returns null if the path is shorter than the specified distance ===
GPolygon.prototype.GetIndexAtDistance = function(metres) {
  // some awkward special cases
  if (metres == 0) return this.getVertex(0);
  if (metres < 0) return null;
  var dist=0;
  var olddist=0;
  for (var i=1; (i < this.getVertexCount() && dist < metres); i++) {
    olddist = dist;
    dist += this.getVertex(i).distanceFrom(this.getVertex(i-1));
  }
  if (dist < metres) {return null;}
  return i;
}

This should allow you to plot the point as desired.

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