Manipulation

If the user carries an object over a long distance, then it is not necessary for her to squeeze or clutch the controller; this would yield unnecessary fatigue. In some cases, the user might be expected to carefully inspect the object while having it in possession. For example, he might want to move it around in his hand to determine its 3D structure. The object orientation could be set to follow exactly the 3D orientation of a controller that the user holds. The user could even hold a real object in hand that is tracked by external cameras, but has a different appearance in the virtual world. This enables familiar force feedback to the user, a concept that is revisited in Section 13.1. Note that an object could even be manipulated directly in its original place in the virtual world, without bringing it close to the user's virtual body [30]. In this case, the virtual hand is brought to the object, while the physical hand remains in place. Having a longer arm than normal can also be simulated [258], to retrieve and place objects over greater distances.