Google Maps API - Midpoint along route [duplicate] - google-maps-api-3

Question

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Midpoint of route in google maps
(1 answer)
Closed 6 years ago.
I've been playing around with the Google Maps/Google directions API. Does anyone have an inkling on how I might be able to find the mid-point along a route, not the geographic midpoint.
Ideally I'd like to find the lat and long values of this midpoint.
Any thoughts? I'm a bit stumped and hoping I may be able to find a suggestion without going crazy trying to find the answer myself.

Answer 1

You can use the GetPointAtDistance prototype from Gisgraphy. The prototype returns a LatLng for a specified distance along a polyline. The following code:
Define a polyline
Determine the half length of this polyline
Use the prototype to return the midpoint LatLng
Extract Lat and Lng from the midpoint LatLng
var polyline = new google.maps.Polyline({
path: [ new google.maps.LatLng(..., ...),
new google.maps.LatLng(..., ...),
... ];
}), //1.
midDistanceLength = polyline.getPath().getLength() / 2, //2.
midDistanceLatLng = polyline.GetPointAtDistance(midDistanceLength),//3.
midDistanceLat = midDistanceLatLng.lat(), //4.
midDistanceLng = midDistanceLatLng.lng(); //4.
//The prototype from Gisgraphy:
google.maps.Polygon.prototype.GetPointAtDistance = function(metres) {
// some awkward special cases
if (metres == 0) return this.getPath().getAt(0);
if (metres < 0) return null;
if (this.getPath().getLength() < 2) return null;
var dist=0;
var olddist=0;
for (var i=1; (i < this.getPath().getLength() && dist < metres); i++) {
olddist = dist;
dist += google.maps.geometry.spherical.computeDistanceBetween (
this.getPath().getAt(i),
this.getPath().getAt(i-1)
);
}
if (dist < metres) return null;
var p1= this.getPath().getAt(i-2);
var p2= this.getPath().getAt(i-1);
var m = (metres-olddist)/(dist-olddist);
return new google.maps.LatLng( p1.lat() + (p2.lat()-p1.lat())*m, p1.lng() + (p2.lng()-p1.lng())*m);
}
google.maps.Polyline.prototype.GetPointAtDistance = google.maps.Polygon.prototype.GetPointAtDistance;

Answer 2

An easiest way is that you can first:
1) Calculate total distance of the path using GMSGeometryDistance, by calculating the distance between every two subsequent points by GMSGeometryDistance function, then summing all the distance.
2) Then you calculate again, and summing in each step. When the sum is about half of the total distance, then you are at the middle point.
Sample code is as following:
    func findTotalDistanceOfPath(path: GMSPath) -> Double {
        let numberOfCoords = path.count()
        var totalDistance = 0.0
        if numberOfCoords > 1 {
            var index = 0 as UInt
            while index  < numberOfCoords{
                //1.1 cal the next distance
                var currentCoord = path.coordinateAtIndex(index)
                var nextCoord = path.coordinateAtIndex(index + 1)
                var newDistance = GMSGeometryDistance(currentCoord, nextCoord)
                totalDistance = totalDistance + newDistance
                index = index + 1
             }
        }
return totalDistance
    }
func findMiddlePointInPath(path: GMSPath ,totalDistance distance:Double) -> CLLocationCoordinate2D? {
    let numberOfCoords = path.count()
    let halfDistance = distance/2
    let threadhold = 10 //10 meters
    var midDistance = 0.0
    if numberOfCoords > 1 {
        var index = 0 as UInt
        while index  < numberOfCoords{
            //1.1 cal the next distance
            var currentCoord = path.coordinateAtIndex(index)
            var nextCoord = path.coordinateAtIndex(index + 1)
            var newDistance = GMSGeometryDistance(currentCoord, nextCoord)
            midDistance = midDistance + newDistance
            if fabs(midDistance - halfDistance) < threadhold { //Found the middle point in route
                return nextCoord
            }
            index = index + 1
        }
    }
    return nil //Return nil if we cannot find middle point in path for some reason
}
There is more to optimize the function. I wrote a detail answer in Swift in here