Evaluation of Virtual Grabbing/Manipulation Techniques

One of the defining features of immersive virtual reality is the ability to interact with 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 metahpor is lacking. Users can only manipulate objects within the arm's reach. To grab other objects, some travel technique must be used. Positioning large objects is difficult with this metaphor, since the user must be so close to them.

Therefore, other techniques are needed. We are researching 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. There are two main categories of techniques.

Arm-Extension Techniques

• 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, it begins to grow, following a polynomial function.
• Fast Go-Go Technique: Same as above, except that no threshold exists for arm extension and the function used grows the arm more quickly.
• Stretch Go-Go Technique: The space around the user's body is divided into three regions at varying distances. In the middle region, the virtual arm is stationary. In the outermost region, the arm grows at a constant rate, and in the innermost region, the arm retracts at a constant rate. The user is given a gauge to aid in using the technique.
• Indirect Stretching Technique: The user presses joystick buttons to extend or retract the virtual arm.

Ray-Casting Techniques

The HOMER Techniques

After testing the above techniques, none proved completely satisfactory. 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.

Therefore, we have created new techniques which combine the best features of the others to produce an easy-to-use, efficient technique for both grabbing and manipulating remote objects. These are 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.

NEW! Taxonomy of Selection and Manipulation Techniques

Large JPEG image of the taxonomy

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