code: public static double atan2(double y, double x) {
          if (y + x == y) {
              return y >= 0 ? HALF_PI : -HALF_PI;
          }
          y = atan(y / x);
          if (x < 0) {
              if (y <= 0) {
                  return y + PI;
              } else {
                  return y - PI;
              }
          }
          return y;
      }
docs: Computes the phase theta by computing an arc tangent of y/x<br> Gets the yaw rotation component in radians when looking into the direction specified
  
  @param y direction
  @param x direction
  @return tangent arc in radians