public static double angle(Coordinate p){
  return Math.atan2(p.y,p.x);
}

public static double angle ( Coordinate p ) { return Math . atan2 ( p . y , p . x ) ; }
returns the angle that the vector from ( 0 , 0 ) to p , relative to the positive x - axis . the angle is normalized to be in the range ( - pi , pi ] .
