Knowledge Base /I /Interaction in VR

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Interaction in VR

Knowledge Base → I

Interaction in virtual reality is often described as the ability of the user to move within the virtual world and to interact with the objects of the virtual world. If the user can explore the virtual world and move objects within, the environment is interactive. Since this definition is ineffective in describing multi-user environments and virtual characters created by AI, it is replaced by action-reaction approaches. Virtual objects and characters within the virtual world

must react to users actions and interactively communicate with them.

Interaction of user with the virtual world can be categorized into the following types:

• Orientation
• Navigation
• Manipulation

Orientation means being able to «look around» in a virtual environment, which develops a sense of presence. Orientation is achieved using full immersive and partial immersive displays. With full immersive displays orientation is naturally achieved. Partial immersive displays have limited orientation that can be enhanced by rotating the virtual world while the user remains still. This can be achieved using a number of devices and techniques, such as using a joystick/trackball and headtracking. By moving a joystick or a trackball from side to side, the user rotates in the virtual world. This method is easy to learn and use, the only disadvantage is the need to use a dedicated device.

When using hypersensitive headtracking, the user’s rotation is enhanced, making full 360º vision possible with a rotation of 160º (e.g. in Panorama). The advantages of this technique are obvious: there’s no extra device to hold, it’s easy to use and even fast movements are tracked. And yet, such headtracking makes it hard to gain a feeling a presence and easy to loose one’s orientation in the virtual world.

When using headtracking with zoning, the user looks towards the edge of the screen and the virtual world rotates in that direction. With this technique, the user preserves his/her feeling of orientation, however freedom of movement is limited thus creating a conflict between orientation in the physical and the virtual world.

Navigation in VR means being able to move/find one’s way through a virtual world. In relation to virtual worlds, speed and absense of constraints is critical as they translate to larger freedom and sense of presence in the virtual world. In relation to virtual objects, precision and special viewpoints are critical. Navigation is achieved using various devices and techniques such as joystick/trackball with 6DOF and the use of navigation zones.

When using a joystick with 6DOF tracking, the user «flyes» in the direction he moves the joystick, providing lots of freedom of movement. However, the joystick is not suited for both fast and precise movements, but rather continuous movements.

When using a trackball with 6DOF tracking, the user «flyes» in the direction he moves the trackball, providing the user with greater feeling of control due to small movements. The trackball is not suited for «flying» long distances, but rather absolute movements.

In the case of headtracking with navigation zones, the user is surrounded by a number of virtual zones. By pointing with his hand the user activates different navigation modes. Examples of navigation modes include: flying up and down, around an object, flying in the pointed directin, etc. The advantages of this technique is that it frees up the user’s hands and it’s easy to combine with manipulation. However, this technique limits freedom of movement and can be hard to comprehend.

Manipulation in VR means being able to manipulate (move, rotate, position, etc) virtual objects.

One of the defining features of immersive virtual reality is the ability to interact manipulate objects in the virtual world in a natural manner. Usually this is achieved by using a real-world metaphor: the user simply reaches out his/her hand, grabs the object, and moves it around using body, arm, and hand motions.

However, this metaphor is lacking. Users can only manipulate objects within the arm's reach. Positioning large objects is difficult with this metaphor, since the user must be so close to them. It is thus crucial to find techniques which allow grabbing/manipulation of local and remote objects, which provide complete control over object position and orientation, and which are efficient and easy-to-use. Virtual object manipulation techniques include «simple» virtual hand, virtual laserbeam ( «ray-casting») or arm-extension techniques.

When using the virtual hand approach, the user’s hand is represented in VR using positiontracking. This approach makes manipulation very natural and easy to rotate and position objects. However the area of manipulation is limited.

In ray-casting, the arm remains at a constant length, and a virtual light ray extending from the hand is used to pick up and manipulate objects. When reeling is added, the object's distance from the user can be controlled by pressing joystick buttons, as in the indirect stretching technique. This approach also makes manipulation very natural and easy to learn, plus the objects at a distance can be selected/picked. However, it is ineffective for selecting small objects at a long distance or for rotation and positioning objects.

Go-Go Technique: The Go-Go technique was introduced by researchers at the University of Washington's Human Interface Technology Laboratory. When the user's physical hand goes beyond a certain distance from the body, the user’s virtual arm begins to grow, following a polynomial function in order to grab or position virtual objects.

Ray-Casting techniques made it easy to grab virtual objects, but manipulation was difficult. Arm-Extension techniques provided natural and efficient manipulation, but getting the hand in the correct position to grab objects was hard.

Thus a new technique which combines the best features of the others to produce an easy-to-use, efficient technique for both grabbing and manipulating remote objects was developed by D. Bowman. This technique is called the HOMER (Hand-Centered Object Manipulation Extending Ray-Casting) Techniques.

Here, the user can grab an object using ray-casting, and manipulate it using natural hand motions. When an object is grabbed, the virtual hand immediately moves to the object and the object becomes attached to the hand. To move the object closer or farther away, either joystick buttons (Indirect HOMER) or a linear mapping of arm motion (Direct HOMER) may be used. These techniques are easy-to-use, extremely efficient, and provide complete control over objects' position and orientation.

In conclusion, it can be said that a good interaction technique in virtual reality depends on the relationship between the interaction technique and

• Interaction device

• Display type (partial or fully immersive)

Developers thus have to optimize combinations of devices and displays in specific contexts.

© 2006—2012, Tradition Group