Interactive Techniques In Computer Aided Design

In a society in which the use of information technology is becoming commonplace it is natural that pictures and images produced by elec tronic means should be increasing in importance as a means of com munication. Computer graphics have only recently come to the atten tion of the general public, mainly through animated drawings, advertise ments and video games. The quality of the pictures is often such that, unless informed of the fact, people are unaware that they are created with the help of computers. Some simulations, those developed in con nection with the space shuttle for example, represent a great and rapid progress. In industry, computer graphic techniques are used not only for the presentation of business data, but also in design and manufacture processes. Such computer-assisted systems are collectively represented by the acronym CAX. In CAD/CAM (computer-assisted design/manufacture), interactive graphic techniques have attained considerable importance. In CAD/CAM systems a dialogue can be established between the user and the machine using a variety of easy to operate communication devices. Due to the recent developments in hardware and software (for modelling, visual display, etc), a designer is now able to make decisions based on the information presented (plans, perspective drawings, graphics, etc) with the help of interactive, graphic techniques. These constitute the most visible and perhaps most spectacular aspect of CAD/CAM systems.

4 lation and optimization. These are essential constituents of the iterative process, leading to a feasible and, one hopes, optimal design. 1.3 Content of the Book In Chapter 2 we present briefly the history of CAD. The main components of CAD systems are identified, and their principal functions described. Economi cal and interdisciplinary aspects are discussed. Chapter 3 starts with a systems analysis of the design process. The notion of a process is introduced as a fundamental tool to describe activities like design as a whole, computer-aided design, program executions, terminal sessions etc. The environment and the resources which the environment must supply for the successful execution of any process are discussed. The problem of modelling the design objects in an abstract schema and the interrelation between the schema and the planning of the individual step in the design are analysed. Chapter 4 concentrates on the interfaces among the components of a CAD system, including the human operator. The problem of mapping an abstract schema onto the capabilities of various programming, command, or data de scription languages is described in detail. Emphasis is laid upon the resource aspect and its influence on the design of CAD systems. The concept of a CAD software machine is introduced, and rules for designing such machines are given.