anchor.diff:  
   *  JME3 offers a `CollisionShapeFactory` that precalculates a mesh-accurate collision shape for a Spatial. You choose to generate a `CompoundCollisionShape` (which has MeshCollisionShapes as its children) because this type of collision shape is optimal for immobile objects, such as terrain, houses, and whole shooter levels.
   *  You set the mass to zero since a scene is static and its mass is irrevelant.
  -*  Add the control to the Spatial to give it physical properties. 
  +*  Add the control to the Spatial to give it physical properties.
   *  As always, attach the sceneModel to the rootNode to make it visible.
   
   [TIP]
  
positive.code: You have learned how to load a “solid physical scene model and walk around in it with a first-person perspective.
  You learned to speed up the physics calculations by using the CollisionShapeFactory to create efficient CollisionShapes for complex Geometries. You know how to add PhysicsControls to your collidable geometries and you register them to the PhysicsSpace. You also learned to use `player.setWalkDirection(walkDirection)` to move collision-aware characters around, and not `setLocalTranslation()`.
  
  Terrains are another type of scene in which you will want to walk around. Let's proceed with learning <<jme3/beginner/hello_terrain#,how to generate terrains>> now. 
  
  '''
  
  
negative.code:   private CharacterControl player;
    private Vector3f walkDirection = new Vector3f();
    private boolean left = false, right = false, up = false, down = false;
  
    //Temporary vectors used on each frame.
    //They here to avoid instanciating new vectors on each frame
    private Vector3f camDir = new Vector3f();
  