Convert longitude and latitude to distance

   private Double  get_distanse(locate a,locate b){
    
        Double result=0.00;
        Double ra=6378140.0;
        Double rb=6356755.0;
        Double lat_a=Math.toRadians(a.getLatitude());
        Double lat_b=Math.toRadians(b.getLatitude());
        Double lon_a=Math.toRadians(a.getLongitude());
        Double lon_b=Math.toRadians(b.getLongitude());
        double pa = Math.atan(rb / ra * Math.tan(lat_a));
        double pb = Math.atan(rb / ra * Math.tan(lat_b));
        double x = Math.acos(Math.sin(pa) * Math.sin(pb) + Math.cos(pa) * Math.cos(pb) * Math.cos(lon_a - lon_b));
        double c1 = (Math.sin(x) - x) * Math.pow((Math.sin(pa) + Math.cos(pb)), 2) / Math.pow(Math.cos(x / 2), 2);
        double c2 = (Math.sin(x) - x) * Math.pow((Math.sin(pa) - Math.cos(pb)), 2) / Math.pow(Math.cos(x / 2), 2);
        double flatten = (ra - rb) / ra;
        double dr = flatten / 8 * (c1 - c2);
        result=ra*(x+dr);
        result=result/1000;
        return result;
    }