How to advance X distance (meters) between two points of latitude and longitude?

Question

I'm simulating a polyline with different stops in Java, I have the distance in meters between these two points, the problem is, that I have to go from point A to point B at a speed of 1 to 3 meters per second, and I will need to take the current coordinates I am every 15 min more or less, how can I do that?

The way between the points are straight lines, and all of this is simulated, not happening in a map or something, I just need to print this info every X time, any help?

Example:

I have the coordinates:

LAT: 51.504870000000004 LNG: -0.21533000000000002

and I have to go at that speed to:

LAT: 51.50475 LNG: -0.21571

So, I have to simulate that I go from A to B at 3 meters second, and I need to know my position (lat/lng) while I'm moving between this two points

There's another question that is more or less the same, the difference is that I can't do this with android, is a Java application.

Answer 1

So you know latA, lngA, latB, lngB. From your question, I assume that you know the speed, it's constant, v = 3 m/s. You can get the start time LocalDateTime tA = LocalDateTime.now(); You want to know your coordinates at some moment of time tX.

In order to do this, I would introduce coefLat and coefLng coefficients for transforming coordinates into meters and back. They use mean radius of Earth and translate degrees into radians:

double coefLat = 180 / Math.PI / 6371000;
double coefLng = coefLat / Math.cos(Math.PI * (latA + latB) / 360);

Then calculate distances by Lat and Lng axis and full distance in meters:

double distLat = (latB - latA) / coefLat;
double distLng = (lngB - lngA) / coefLng;
double dist = Math.sqrt(distLat * distLat + distLng * distLng);

double fullTime = dist / v; // Full time needed to pass from A to B in seconds

After some time of moving, find duration and get current coordinates:

LocalDateTime tX = LocalDateTime.now(); // get current time
long dT = Duration.between(tA, tX).getSeconds(); // in seconds
double ratio = dT / fullTime;

double latX = latA + coefLat * ratio * distLat;
double lngX = lngA + coefLng * ratio * distLng;

Please also see this answer

The full code:

public class GetCurrentCoords {

    public static void main(String[] args) {

        LocalDateTime tA = LocalDateTime.now();
        double latA = 51.504870000000004;
        double lngA = -0.21533000000000002;
        double latB = 51.50475;
        double lngB = -0.21571;

        double coefLat = 180 / Math.PI / 6371000;
        double coefLng = coefLat / Math.cos(Math.PI * (latA + latB) / 360);

        double distLat = (latB - latA) / coefLat; // meters
        double distLng = (lngB - lngA) / coefLng; // meters

        double dist = Math.sqrt(distLat * distLat + distLng * distLng);
        System.out.println("distLat = " + distLat + "m; distLng = " + distLng + "m; full dist from A to B = " + dist + "m");
        double v = 3;

        double fullTime = dist / v; // seconds
        System.out.println("full time from A to B = " + fullTime + "s");

        // let's move for 4 seconds
        try {
            TimeUnit.SECONDS.sleep(4);
        } catch (InterruptedException ex) {
            Logger.getLogger(GetCurrentCoords.class.getName()).log(Level.SEVERE, null, ex);
        }

        LocalDateTime tX = LocalDateTime.now(); 
        long dT = Duration.between(tA, tX).getSeconds();
        double ratio = dT / fullTime;

        double latX = latA + coefLat * ratio * distLat;
        double lngX = lngA + coefLng * ratio * distLng;

        System.out.println("Moving " + dT + " seconds; latX = " + latX + "; lngX = " + lngX);
     }
}