public static double DistanceBetweenPoints(double x1, double y1, double a1, double x2, double y2, double a2)
{
    double r = R + Math.Min(a1, a2);
    double scfY = Math.Sin(y1 * Deg2Rad);
    double sctY = Math.Sin(y2 * Deg2Rad);
    double ccfY = Math.Cos(y1 * Deg2Rad);
    double cctY = Math.Cos(y2 * Deg2Rad);
    double cX = Math.Cos((x1 - x2) * Deg2Rad);
    double sizeX1 = Math.Abs(r * Math.Acos(scfY * scfY + ccfY * ccfY * cX));
    double sizeX2 = Math.Abs(r * Math.Acos(sctY * sctY + cctY * cctY * cX));
    double dx = (sizeX1 + sizeX2) / 2.0;
    double dy = r * Math.Acos(scfY * sctY + ccfY * cctY);
    if (double.IsNaN(dx)) dx = 0;
    if (double.IsNaN(dy)) dy = 0;
    double d = Math.Sqrt(dx * dx + dy * dy);
    double hd = Math.Abs(a1 - a2);
    return Math.Sqrt(d * d + hd * hd);
}

 //GpsCoordinates is lat, lng, and altitude in meters
        GpsCoordinates A = new GpsCoordinates(48.332300, -70.992836, 0);
        GpsCoordinates B = new GpsCoordinates(48.332200, -70.992836, 0.2); //small difference in latitude, 200 meters difference in altitude

        double dx, dy;
        OnlineMapsUtils.DistanceBetweenPoints(A.Longitude, A.Latitude, B.Longitude, B.Latitude, out dx, out dy);

        Debug.Log("distance between A and B (no altitude taken into account) : " + Math.Sqrt(dx * dx + dy * dy) * 1000 + " m");

        OnlineMapsUtils.DistanceBetweenPoints(A.Longitude, A.Latitude,(float)A.Altitude, B.Longitude, B.Latitude,(float)B.Altitude, out dx, out dy);

        Debug.Log("distance between A and B (altitude should matter in the result): " + Math.Sqrt(dx * dx + dy * dy) * 1000 + " m");
        
        //representation of the two points on the map :

        string label = "PointA";
        OnlineMapsMarker3D marker = OnlineMapsMarker3DManager.instance.Create(A.Longitude, A.Latitude, prefab);
        marker.prefab.name = label;
        marker.tags.Add(label);
        marker.altitudeType = OnlineMapsAltitudeType.relative;
        marker.altitude = (float)A.Altitude*1000;

        label = "PointB";
        OnlineMapsMarker3D marker2 = OnlineMapsMarker3DManager.instance.Create(B.Longitude,B.Latitude, prefab);
        marker2.prefab.name = label;
        marker2.tags.Add(label);
        marker2.altitudeType = OnlineMapsAltitudeType.relative;
        marker2.altitude = (float)B.Altitude*1000;