How to return from atan2 angle back to coordinate?

Question

satellite navigation

With the help of atan2 and some trigonometric functions, I'm looking for the distance between two gps coordinates, but now the goal is to go back to the coordinates. Please help me find "x" and "y" which are in atan2.

final double RADIUS = 6372795;
    double a1 = 51.509069,a2 = 31.325302,b1 = 51.508628,b2 = 31.325986;
    double lat1,lat2,long1,long2;
    ////////////////////////////////////////////
    lat1 = a1*Math.PI/180;
    lat2 = b1*Math.PI/180;
    long1 = a2*Math.PI/180;
    long2 = b2*Math.PI/180;
    System.out.println ("x1-"+lat1+" y1-"+long1);
    System.out.println ("x2-"+lat2+" y2-"+long2);
    
    ///////////////////////////////////////////////
    System.out.println("косинусы и синусы широт и разницы долгот");
    
    double cl1 = Math.cos(lat1);
    double cl2 = Math.cos(lat2);
    double sl1 = Math.sin(lat1);
    double sl2 = Math.sin(lat2);
    
    System.out.println("косинусы "+ cl1+" "+cl2);
    System.out.println("синусы "+ sl1+" "+sl2);
    
    double delta = long2-long1;
    double cdelta = Math.cos(delta);
    double sdelta = Math.sin(delta);
    
    System.out.println("delta "+ delta+" "+cdelta +" "+sdelta);
    
    /////////////////////////////////////////////////////
    double y = Math.sqrt(Math.pow(cl2*sdelta, 2)+ Math.pow(cl1*sl2-sl1*cl2*cdelta, 2));
    double x = sl1*sl2+cl1*cl2*cdelta;
    
    double ad = Math.atan2(y, x);
    double dist = ad*RADIUS;
    System.out.println ("distanse - "+dist);

Answer 1

googleпрямая геодезическая задача

Answer 2

There are many such points on the sphere. For example, the set of points on the sphere equidistant from the chosen one on dist ( = ad*RADIUS)will be a circle.