page 125

•Every CAD system uses a graphical display for user interpretation of the final part.

•The display methods discussed in the computer graphics section are all used in CAD packages. (Please refer to that section for examples, and explanation of how each display method affects the user).

•There are many techniques possible with computer graphics that make on screen designs easier to understand.

-Dimensioning

-Placed manually, but updates when dimensions change.

-Annotation - the user may add comments to drawings

-text with a leader pointing to something

-text alone

-tolerances

-Drawing information

-Graphics effects

-Fill Styles - hatching and other patterns selected

-Line Styles - such as hidden, shadow, phantom, etc.

-Color - helps differentiate when there are many lines

DI:15.6 USER DIRECTED CHANGES TO THE GEOMETRIC MODEL

•This feature is of the greatest importance to a user

•Some onscreen input selection features are,

-Boxes - a good example of this method is the zoom boxes

-Types - all objects of a certain type are selected

-Last - last object created

-All - all visible objects

-Names - in some systems parts are named, and these can be used for reference.

-Markers - symbolic markers can be placed on the screen to allow easy differentiation between object (like in Ideas)

-Layers - drawings can be layered up, which allows easy separation of distinctive parts. One example is a factory layout, including separate layers for machines, plumbing, electrical, HVAC, etc.

•Objects often require manipulation on the screen, and certain parameters defined by a number of techniques,

-Translation

-select two points (they define a translation vector)

-angle and distance

-select a line (a direction vector)

page 126

-move a point to a point

-interpolate

-etc.

-Rotation

-about a pivot point by 1 angle (2 angles for 3D)

-about an axis by an angle

-Mirroring

-mirror over a line/plane

-Magnification

-a magnification about a point by a factor

-Copying

-a simple copy

-a copy with an offset for each copy

-a copy with a rotation for each copy

DI:15.6.1 Modern Hardware for CAD Systems

•The CRT is taken for granted now, but previously CAD systems underwent many metamorphosis.

•The array of current and previous hardware input devices are,

-keyboard

-mouse

-tablet

-button/dial boxes

-light pen

-touch screen

-track balls

-joy sticks

-punched cards

-CMMs

-scanners

-3D scanners

Device	Resolution	Speed	Cost	Fatigue
Mouse	Medium	High	Low	Medium
Keyboard	Exact	Low	Low	Medium
Tablet	High	High	High	Low
Position Joystick	Medium	High	Low	Low
Velocity Joystick	High	Medium	Low	Low
Light pen	Low	High	Low	High