code: public static double getDistance(Localizable a, Localizable b)
      {
          Check.notNull(a);
          Check.notNull(b);
  
          final double x = b.getX() - a.getX();
          final double y = b.getY() - a.getY();
  
          return StrictMath.sqrt(x * x + y * y);
      }
docs: Get distance of two points.
  
  @param a The first localizable (must not be <code>null</code>).
  @param b The second localizable (must not be <code>null</code>).
  @return The distance between them.
  @throws LionEngineException If invalid argument.