Find point on the route using GraphHopper

Question

I am using GraphHopper for finding a route between points. I want to predict the location of the vehicle at the given time t if it is moving at an average speed of x. GraphHopper has a module for finding isochrone but I can't figure out how I can run it on a single route. Below is the code which I am currently using

    List<GHPoint> points = new ArrayList<>();

    points.add(origin);

    for (GHPoint pnt : waypoints) {
        points.add(pnt);
    }

    points.add(destination);

    GHRequest req = new GHRequest(points).
            setWeighting("shortest").
            setVehicle("car").              
            setLocale(Locale.US);

    GHResponse rsp = graphHopper.route(req);

    // first check for errors
    if(rsp.hasErrors()) {
        // handle them!
        // rsp.getErrors()
        List<Throwable> errors = rsp.getErrors();
        return null;
    }

    PathWrapper bestPath = rsp.getBest();

Answer 1

Thanks to @Jamie i got the interpolated point by lopping the coordinate list in LineString. You can get the LineString by using getPoints().toLineString method i.e. bestPath.getPoints().toLineString(false).

The distance was calculated like this by

   distance = (avgSpeedKMPerHr/ 3.6 ) * timeSec;

Below is the function which is used

  //distacne in meters which was calucletd 
public Point interpolatePointAlogLine(LineString line,double distance) throws 
   NoSuchAuthorityCodeException, FactoryException
{       
    GeodeticCalculator calculator = new GeodeticCalculator(CRS.decode("EPSG:4326")); 
    GeometryFactory geometryFactory = new GeometryFactory(new PrecisionModel(PrecisionModel.FLOATING), 4326);

    List<Coordinate> coordinates = new ArrayList<Coordinate>();
    Collections.addAll(coordinates, line.getCoordinates());
    double accumulatedLength = 0;

    if(distance >= line.getLength())
        return geometryFactory.createPoint(line.getEndPoint());

    for (int i = 0; i < coordinates.size(); i++)
    {

        Coordinate c1 = coordinates.get(i);
        Coordinate c2 = coordinates.get(i + 1);

        calculator.setStartingGeographicPoint(c1.x, c1.y);
        calculator.setDestinationGeographicPoint(c2.x, c2.y);

        double length = calculator.getOrthodromicDistance();

        if (length + accumulatedLength >= distance) 
        {
            double offsetLength = distance - accumulatedLength;
            double ratio = offsetLength / length;
            double dx = c2.x - c1.x;
            double dy = c2.y - c1.y;

            Coordinate iPoint = new Coordinate(c1.x + (dx * ratio), 
                    c1.y + (dy * ratio));

            return geometryFactory.createPoint(iPoint));
        }
        else {
            accumulatedLength += length;
        }
    }
    return null;
}