Virtual reality departs from conventional Human-Computer Interaction (HCI) and naturally requires a different set of user input tools. This paper will examine the various types of input devices that have been developed for use with virtual reality.
When you move your hand, the glove picks up the movement and sends an electrical signal to the computer which then translates the movement from real space into virtual space. Often, you are able to see your virtual hand in the virtual world. This greatly aids in the hand-eye coordination, necessary for any kind of positioning in a three dimensional world.
Besides being used to perform tasks that we use our hands in the real world for, researchers soon realized that this same glove could be used for architectural walk-throughs, scientific visualization, or any number of other applications. [AUKS92] This is done by assigning meaning to hand gestures.
The second tool measures the absolute position (X, Y, and Z axis) andthe orientation (roll, pitch, and yaw) of the hand. This tool has two parts: a stationary transmitter, and a receiver that is placed on the glove. Both the transmitter and the receiver are made up of three coils of wire at right angles. The transmitter has an electrical current passing through and it creates a magnetic field. When the glove moves, the receiver on it produces three distinct electrical charges. By measuring these charges, we can calculate the position and orientation of the glove. This system is known as the Polhemus magnetic positioning system. [AUKS92]
One problem with the DataGlove is that it requires recalibration for each user as it is very sensitive to knuckle position. Also, it is about one hundred times more expensive than the PowerGlove, which will be described next.
For flex-measuring, the PowerGlove has a strip of mylar plastic coated with electrically conductive link. This strip is placed along each finger and when a finger is flexed, the electrical resistance changes. The change corresponds to the degree bent.
For absolute position and orientation, the PowerGlove uses the simpler ultrasonic positioning technique. Receivers pick up the signals from two ultrasonic transmitters on the glove and translate them into a position in space.
Like the DataGlove, the PowerGlove needs recalibration for different users. Also, it is less accurate than the DataGlove. However, the PowerGlove is more rugged and easier to use than the DataGlove.
Not only is a DHM more accurate than a PowerGlove or a DataGlove, it is also able to measure the radial-ulnar deviation (side to side motion) of each finger. In addition, it takes into account the fact that a human finger has three sections, rather than two, which the DataGloves and PowerGloves are capable of measuring. This precision makes it extremely useful for any application that requires a high level of control, such as controlling dexterous robotic hands.
DHMs are also less sensitive than either the dataglove or the powerglove with respect to different hand sizes and placement on the fingers. However, it is rather clunky to work with.
Mice and joysticks usually have two degrees of freedom, although there are mice designed with six degrees of freedom. Either ultrasonic, electromagnetic, or gyroscopic tracking is used for the 6D mice.
In the virtual world, a wand does not necessarily have to appear as a pointing device. It can be represented as a drill, paintbrush, spray gun, or even an ice-cream cone. One of the strengths of virtual environments is that the appearance of an object can be whatever the designer chooses -- it need bear no resemblance to the object's physical appearance. [PIME92]
A wand is very easy and intuitive to use. Regardless of its representation in the virtual world, most of the actions involve just 'point and click' with the wand.
A force ball is easy and intuitive to use; you simply push the ball in the direction that you want to move. Typically, a user becomes very comfortable with the device after fifteen or twenty minutes of use. Also, a force ball requires very little space as there is no movement. In addition, you do not have to hold it in midair, as you would using a 6D mouse. Most force balls have programmable buttons for a developer to configure to suit the needs of the application.
However, uses of a force ball are limited to navigation and selection. It is not suitable for interactions or issuing commands.
It is also possible that in the future we can detect hand movement by wearing a bracelet that can detect hand muscle activities, thereby replacing a more cumbersome glove.
Although we have gone a long way in bringing voice recognition technology from mainframes to personal computers, the systems nowadays are still far from perfect, especially when it comes to understanding continuous speech. Most system requires training, where the user has to repeat a word many times in various ways to let the computer recognize the different patterns of the sound. It should be noted that the computer does not actually understand the word, but merely stores the digitized pattern of the word for later comparisons to a voice command. In addition, most systems are limited to a vocabulary in the hundreds of words. [RHEI91]
Voice recognition as an input device is limited in two ways. First, there are times when it actually decreases efficiency. Suppose you want to draw a line. It's definitely faster if you just enter the coordinates of the line using a keyboard than to say "Draw a line starting from coordinates such and such to coordinates such and such". Second, the computer may have difficulty understandings words under different contexts, or words that sound alike. For example, "You have an e-mail" may be understood as "You have any male."
[PIME93] Ken Pimentel, Kevin Teixeira, "Virtual Reality: through the new looking glass", Intel/Windcrest/McGraw Hill,1993.
[RHEI91] Howard Rheingold, "Virtual Reality", Touchstone, 1991.