Various devices are available for data input on graphics workstations. Most systems have a keyword and one or more additional devices specially designed for interactive input. These include a mouse, trackball, joystick, digitizers, dials, and buttons boxes. Some other input devices used in particular applications are data gloves, touch panels, image scanners, and voice systems.
An alphanumeric keyboard on a graphics system is used primarily as a device for entering text strings. The keyboard is an efficient device for inputting such non-graphic data as picture labels associated with a graphics display. Keyboards can also be provided with features to facilitate entry of screen coordinates, menu selections, or graphics functions.
Cursor-control keys and function keys are common features on general-purpose keyboards. Function keys allow users to enter frequently used operations in a single keystroke, and cursor-control keys can be used to select displayed objects or coordinate positions by positioning the screen cursor. Other types of cursor-positioning devices, such as trackball or joystick, are included on some keyboards. Additionally, a numeric keypad is often included on the keyboard for fast entry of numeric data.
For specialized applications, input to a graphics application may come from a set of buttons, dials, or switches that select data values or customized graphics operations. Buttons and switches are often used to input predefined functions, and dials are common devices for entering scalar values. Real numbers within some defined range are selected for input with dial rotations. Potentiometers are used to measure dial rotations, which are then converted to deflection voltage for cursor movement.
A mouse is a small hand-held box used to position the screen cursor. Wheels or rollers on the bottom of the mouse can be used to record the amount and direction of movement. Another for detecting mouse motion is with an optical sensor. For these systems, the mouse is moved over a special mouse pad that has a grid of horizontal and vertical lines. The optical sensor detects movement across the lines in the grid.
Since a mouse can be picked up and put down at another position without a change in cursor movement, it is used for making relative changes in the position of the screen cursor. One, two or three buttons are usually included in the top of the mouse for signaling the execution of some operation, such as recording cursor position or invoking a function. Most general-purpose graphics systems now include a mouse and a keyboard as the major input devices. Additional devices can be included in the basic mouse design to increase the number of allowable input parameters.
Trackball and Spaceball
As the name implies, a trackball is a ball that can be rotated with the fingers or palm of the hand, to produce a screen-cursor movement. Potentiometers, attached to the ball, measure the amount and direction of rotation. Trackballs are often mounted on a keyboard or other devices such as the z mouse. While a trackball is a two-dimensional positioning device, a space ball provides six degrees of freedom. Unlike the trackball, a space ball does not actually move. Strain gauges measure the amount of pressure applied to the spacebar to provide input for spatial positioning and orientation as the ball is pushed or pulled in various directions. Spaceball is used for three-dimensional positioning and selection operations in virtual- reality systems, modeling, animation, CAD, and other application.
A joystick consists of a small, vertical lever mounted on a base that is used to steer the screen cursor around. Most joysticks select screen positions with actual stick movement others respond to pressure on the stick. Some joysticks mounted on a keyboard others function as stand-alone units.
The distance that the stick is moved in any direction from its center position corresponds to screen-cursor movement in that direction potentiometers mounted at the base of the joystick measure the amount of movement, and springs return the stick to the center position when it is released. One or more buttons can be programmed to act as input switches to signal certain actions once a screen position has been selected.
A data glove that can be used to grasp a “virtual” object. The glove is constructed with a series of sensors that detect hand and finger motions. Electromagnetic coupling between transmitting antennas and receiving antennas is used to provide information about the position and orientation of the hand. The transmitting and receiving antennas can each be structured as a set of three mutually perpendicular coils, forming a three-dimensional Cartesian coordinate system. Input from the glove can be used to position or manipulate objects in a virtual scene. A two-dimensional projection of the scene can be viewed on a video monitor, or a three-dimensional projection can be viewed with a headset.