Computer Aided Engineering Design

INTRODUCTION 7

It provides high interactivity, hierarchical data structuring, real time graphic data modification, and
support for geometric transformations. These standards provide the core of graphics including basic
graphic primitives such as line, circle, arc, poly-lines, poly-markers, line-type and line-width, text,
fill area for hatching and shading, locators for locating coordinates, valuators for real values for
dimensioning, choice options and strings. Around such standard primitives, almost all standard
software for CAD is written. They also include the device drivers for standard plotters and display devices.
Another comprehensive standard is IGES to enable the exchange of model databases among CAD/
CAM systems. IGES contains more geometric entities such as, curves, surfaces, solid primitives, and
Boolean (for Constructive Solid Geometry) operations. Wire-frame, surface modeling and solid
modeling software can all be developed around IGES. It can transmit the property data associated
with the drawings which helps in preparing, say, the bill of materials. Though these standards appear
veiled or at the back end, they play a crucial role in creation of the application software.

1.5 Designer-Computer Interaction

A CAD/CAM software is designed to be primarily interactive, instructive and user-friendly wherein
a designer can instruct a computer to perform a sequence of tasks ranging from designing to manufacture
of an engineering component. The front end of a software is a graphical user interface or GUI while
the back end comprises computation and database management routines. The front end is termed so
as a user can visually observe the design operations being performed. However, computation and data
storage routines are not very apparent to a designer, which is why they may be termed collectively
as the back end of the software. In most CAD software, the GUI is divided into two parts (or
windows) that appear on the display device or screen (Figure 1.1): (i) the visual manifestation or the

Figure 1.1 Generic appearance of the Front end of a CAD software

Graphics window Command window

Icons or push

buttons