Home Contact Us
Contact Us


Section 1 Introduction

Section 2 Computer-aided Design (CAD)

Section 3 Types of CAD 


Description:  The purpose of this unit is to enable you to reliably produce services layout, schematic and detail drawings to commercially acceptable standards for complex installations using industry standard computer aided drawing software.

Author:  Gates MacBain Associates

Section 1  Introduction

This unit is only able to provide you with an introduction to the subject of computer-aided design; it is not a course in itself as this requires the application of knowledge which can only be acquired by practice. In order to become proficient at this you are advised to undergo a specific course related to the practical aspects of the subject; although the Introduction to AutoCad book listed in the next chapter does provide an excellent step by step guide to producing drawings.

Section 2  Computer-aided Design (CAD)

Aims and Objectives

At the end of this section you should be able to:
  • Explain the purpose of CAD.

The letters CAD stand for computer-aided design or drafting. Architects, architectural technicians and engineers use CAD software to create plans and construction drawings. 

Before the age of computers, drawings and blueprints were drafted by hand, which was a time consuming task and it meant that any alterations would involve the redrawing and replacement of plans or drawings.  CAD is more efficient because the software records lines as vectors based on mathematical equations. Portions of a drawing can be twisted, stretched, or moved. The picture as a whole will automatically adjust which then just needs to be printed off.

CAD also has a number of other advantages in that the drafter can:
  • Switch between two-dimensional (2D) and three-dimensional (3D) views.
  • Zoom in and out for close-up and distant views.
  • Rotate images to view them from different perspectives.
  • Change the scale of images: When one value changes, related values are automatically adjusted.
  • Manipulate the shape of images: Changing one portion of an image automatically changes the entire picture.
  • create photo simulations.

An introduction to the technical aspects of CAD can be found at the link below while the CAD Software link provides an excellent introduction to the whole subject. It is also worth looking at the video below.

There are many CAD software applications (see Links to vendors).  One of the most popular programmes is AutoCAD and details of this can be found by clicking on the AutoCAD link below.

It is possible to find tutorials on the web (See Tutorials link) but CAD is a specialist subject area and if you are interested in it you should do a special course, your tutor may be able to advise you on this. 



  • Roberts, J, (2005)  Introduction to AutoCad 2005,Payne-Gallway; Harlow


Self-Assessment Task

  • Discuss the use and advantages of using CAD over a drawing board.

Section 3  Types of CAD

Aims and Objectives

At the end of this section you should be able to:
  • Describe the types of CAD systems

The type of design and drafting required will determine the kind of software package that is most suitable. CAD programs vary by the way the drawing is plotted and this will depend on the type of drawing--mechanical, architectural, etc, you will be using it for. The options available are:


This is the most basic type of computer-aided drafting. The design is created by plotting along the X- and Y-axes. Designs are made up of lines, circles, ovals, slots, curves, etc, they  have no depth to them, as they are displayed by their outlines only using the  basic geometric figures. Drawings are in two dimensions have a very flat appearance. These types of programs are useful for architects and other professionals who do not require any depth to provide a representation.

Two-and-a-half Dimensional

Two-and-a-half dimensional CAD allows the creation of psuedo-three-dimensional drawings. This is typically done through isometric projection which creates a sense of depth.


Three-dimensional computer-aided drawing programs are some of the more expensive CAD programs. They may use NURBS (Non-uniform rational basis spline  -  a mathematical model commonly used in computer graphics for generating and representing curves and surfaces), wire frames or solids to create three-dimensional drawing architecture. The design has true depth to it, allowing the designer to rotate the design 360 degrees around three different axes. This is one of the most accurate representations of how a design will look when actually produced.

Profession Specific

In addition to differences between computer-aided drafting and design programs according to how they represent drawings, companies make programs specifically for use by drafters working in certain trades. For example, Autodesk, the creator of AutoCAD, makes a special AutoCAD for both architecture and civil engineering. These programs allow for ease of drafting by incorporating and streamlining functions that would be irrelevant or cumbersome in a more general package. For example, architectural CAD programs include functions for laying out wall.

Tools in CAD

CAD incorporates a number of tools or functions which speed up the process of design. These tools will depend on the package and the manufacturer.  


Self-Assessment Task

  • Describe the types of CAD systems stating the type of work that each type would be most appropriate for.

Site Map