One of the simplest ways to select an object in the virtual world is with the virtual laser pointer, which was described in Section 10.2. Several variations may help to improve the selection process. For example, the user might instead hold a virtual flashlight that illuminates potential selections. The field of view of the flashlight could be adjustable . A virtual mirror could be placed so that a selection could be made around a corner. Chapter 5 of  offers many other suggestions.
With a pointer, the user simply illuminates the object of interest and presses a button. If the goal is to retrieve the object, then it can be immediately placed in the user's virtual hand or inventory. If the goal is to manipulate the object in a standard, repetitive way, then pressing the button could cause a virtual motor program to be executed. This could be used, for example, to turn a doorknob, thereby opening a door. In uses such as this, developers might want to set a limit on the depth of the laser pointer, so that the user must be standing close enough to enable the interaction. It might seem inappropriate, for example, to turn doorknobs from across the room!
If the object is hard to see, then the selection process may be complicated. It might be behind the user's head, which might require uncomfortable turning. The object could be so small or far away that it occupies only a few pixels on the screen, making it difficult to precisely select it. The problem gets significantly worse if there is substantial clutter around the object of interest, particularly if other selectable objects are nearby. Finally, the object may be partially or totally occluded from view.
Steven M LaValle 2016-12-31