private bool IsNavigable(Vector3 pos)
 {
     foreach (Entity entity in XNAGame.Instance.Children)
     {
         if (entity is Obstacle)
         {
             Obstacle obstacle = (Obstacle)entity;
             if (obstacle.isInside(pos, 2.0f))
             {
                 return(false);
             }
         }
     }
     return(true);
 }