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Graphics are essential for planning buildings, completing engineering designs, estimating quantities of materials and relative costs and, lastly, communicating to the builder all the information that the designer has formulated.
Computing, drafting, typing and printing technologies have changed dramatically since the early 1980s. Slide rules have been replaced by calculators and computers. Drawing tables, pencils, pens, T-squares and erasers have been replaced by computers. Various computer hardware systems been developed to process high-quality graphics at very high speeds and to keep project costs to a minimum. These technologies are known as computer-aided design and drafting (CADD).
Computer-aided design and drafting [CADD]
CADD is an electronic tool for preparing quick and accurate drawings with the aid of a computer instead of the traditional tools (pencils, ink, rulers and paper). Unlike the traditional methods of preparing drawings on a drawing board, CADD enables high-precision drawings to be created on a computer.
CADD software has generally replaced the traditional drawing board in drafting offices. In the 1990s, CADD was used only for specific high-precision engineering applications. This was a result of the high price of CADD software, which made it accessible to only a few professionals. However, as prices have fallen there has been a significant increase in the use of CADD software and it is now widely used by most professionals.
CADD software can be used to produce two-dimensional (2D) drawings directly or to build a three-dimensional (3D) model of projects, from which the software can extract 2D drawings that will be printed on paper. Some CADD software also includes modules for rendering realistic images.
Much more can be achieved using CADD than with the traditional drawing board. Some of the major capabilities are: presentations, flexibility in editing, units and accuracy levels, storage and access for drawings, sharing CADD drawings, project reporting, engineering analysis, computer-aided manufacturing (CAM), design and add-on programmes.
Using CADD to produce a building drawing has the following advantages:
* The drawings are clean, neat and highly presentable.
* The drawings can be subdivided into smaller parts that can be reused or worked on by several people.
* Updating drawings is much faster than with hand-drawn plans that would have to be redrawn.
* Drawings can be presented in different formats, thereby facilitating transfer from one system to another.
* Several integrated tools are used to check drawings for errors.
* It is possible to work with real world units ï¿½ the CADD system performs scaling automatically to fit any size of paper.
Figure 3.1 A modern drafting office
It should also be noted that current CADD systems are moving away from traditional drawing-oriented solutions towards fully featured architectural solutions (i.e. building information processing), which can be used not only to design a project, but also to manage the enormous quantities of information (such as materials, prices or utilization) that go into an architectural project.
CADD hardware refers to the physical components of a CADD system. The main hardware components of a CADD system include: system unit, central processing unit, memory, hard disk, floppy disk, CD-ROM, external storage devices, monitor, printers and plotters, keyboard, digitizer and mouse.
A CADD programme contains hundreds of functions to perform specific drawing tasks. A task may involve drawing an object, editing an existing drawing, displaying a view of the drawing, printing or saving it, or controlling any other computer operation. The functions contain a number of commands used to specify exactly what to do and how it should be done. The functions are organized into modules that provide easy access to all commands. The programme is divided into modules such as draw, edit, data output, function control, data storage and management. CADD software may also incorporate a number of specialized functions such as layers, databases and 3D.
CADD user interface
A CADD user interface provides the environment and the tools to allow the user and the computer to communicate. Each CADD programme establishes an environment that best suits its purpose. The goal is to make working with CADD efficient. Most programmes use a graphical user interface (GUI) to communicate with the user. The GUI provides visual aids for quick data entry. Tools are provided that enable users to select functions, enter textual or mathematical data, locate points in the drawing window, select objects in the drawing window, etc.
A user may communicate with the CADD system by:
* using the menu bar;
* entering commands in the command window;
* using the tool buttons;
* using the dialogue boxes;
* working in the drawing area.
Components of a CADD drawing
CADD drawings are created by drawing individual components of the drawing, such as lines, arcs, dimensions and symbols. CADDï¿½s drawing functions are used to create each component of a drawing, such as lines, arcs, circles, ellipses, symbols, text, dimensions, pointers, polylines, borders and patterns. Most drawings can be completed using these CADD components.
The coordinate system is a method of locating points in the drawing area. It is used to locate points by specifying distances from a fixed reference point. A point can be located by giving its distance in the horizontal plane, vertical plane, measuring along an angle, etc.
The coordinate system is used when a function requires data input in the form of point locations. The most common coordinate systems are:
* Cartesian coordinates;
* polar coordinates.
CADD allows users to define a coordinate system that can help simplify drawing. This measurement mode is very useful when working with a complex drawing that has many odd angles.
CADD filing system
Drawings created in CADD can be stored in the computer hard drive as memory blocks called files. The files can be named as desired by the user. This is important as it enables the files to be accessed when required in the future. For example if the work on a specific file is to be postponed to another time or modification are required on a file for another project or the files need to be transferred electronically.
The files dealt with in a given drawing office can run into hundreds. Thus it is important that proper file management be put in place. This made easy by the computer as it allow files to be stored in directories and subdirectories. Files organized in this manner are easier to trace.
Drawing tools in CADD
The basic drawing tools in CADD include the following:
* line types;
* flexible curves;
* drawing arcs and circles;
* drawing ellipses and elliptical arcs;
* adding text to drawings;
* text styles;
* setting dimension styles;
* adding hatch patterns to drawings;
* drawing symbols;
* drawing arrows.
There are a number of line types available in CADD that can be used to enhance drawings. They include continuous lines, dotted lines, centre lines and construction lines. With CADD it is possible to follow both geometrical and engineering drawing standards.
CADD has the ability to draw parallel lines simultaneously once the user indicates a start-point and an end-point. These lines can be used to draw heavy lines or double lines e.g. they can be used to draw the walls of a building plan, roads on a site map, or any other presentation that requires parallel lines.
CADD can draw flexible curves that can be used to project almost any shape. Such curves can be used to project the smooth curves of a sculpture, the contours of a landscape plan, or roads and boundaries. To draw a flexible curve, indicate the points through which the curve will pass. Draw a uniform curve passing through the marked points. The sharpness of the curves, the roughness of the lines and their thickness can be controlled using the relevant commands.
CADD provides many advanced techniques for drawing arcs and circles, which can simplify many geometrical drawing problems. An arc can be drawn by specifying the circumference and radius, the radius and rotation angle, or the chord length and radius. Arcs are drawn so accurately that a number of engineering problems can be solved graphically rather than mathematically. Assuming that you need to measure the circumference of an arc, you can do so by selecting the specific arc and the exact value is then displayed.
Ellipses are much easier to draw with CADD than on a drawing board. On a drawing board, the template of the correct size must be identified or a series of arcs must be drawn individually to create an ellipse, while with CADD all that is required is to specify the size of the ellipse.
Fine lettering can also be added to drawings with CADD, using text to write notes and specifications and to describe the components of a drawing. Text created using CADD is neat and stylish and easy to edit. Writing text with CADD is as simple as typing it on the keyboard and then positioning it anywhere on the drawing. It is also possible to choose from a number of available fonts and to use different letter sizes. The text appearance is controlled by factors such as the text height, height-to-width ratio and inclination of letters, special effects, text alignment and text font.
CADD dimensioning functions provide a fast and accurate means of drawing dimensions. To draw a dimension, all you need to do is indicate the points that need to be dimensioned. CADD automatically calculates the dimension value and inserts all the necessary annotations. The annotations that form a dimension are the dimension line, dimension text, dimension terminators and extension lines.
The appearance of each of these elements can be controlled by changing the dimensioning defaults. The following are the most commonly used methods for drawing dimensions: drawing horizontal and vertical dimensions; dimensioning from a base line; dimensioning arcs and circles; drawing dimensions parallel to an object and dimensioning angles.
The appearance of drawings can be enhanced using the hatch patterns available in a CADD system. The patterns can be used to emphasize portions of the drawing and to represent various materials, finishes and spaces. Several ready-made patterns, which are quite easy to draw, are available in CADD and can be instantly added to drawings.
Moreover, there is no need to draw the individual elements of a pattern one by one. Simply specify an area where the pattern is to be drawn by selecting all the drawing objects that surround the area. The selected objects must enclose the area completely (for instance a closed polygon). When the area is enclosed, a list of available patterns is displayed and the pattern selected then fills the specified area.
Symbols provide a convenient way of drawing geometrical shapes. This CADD function is an electronic form of the multipurpose templates commonly used on a drawing board (e.g. to draw a geometrical shape, such as a pentagon or hexagon, select an appropriate symbol from the menu, specify the size of the symbol, and it is drawn at the indicated point). There are also special symbol templates that are used to represent the usual architectural symbols.
Arrows in a drawing are commonly used to indicate which note or specification relates to which portion of the drawing, or to specify a direction for any reason. There are several arrow styles available in CADD programmes, ranging from simple two-point arrows to arrows passing through a number of points, and from simple to fancy arrow styles. To draw an arrow, simply indicate the points through which the arrow must pass.
The edit module provides great flexibility in changing CADD drawings. If only the drawing functions of CADD were available, then it would probably take the same time to complete a drawing as it would on a drawing board. But CADDï¿½s editing functions make CADD a dynamic tool that results in significant savings in terms of time.
Changes that may look extremely difficult on a drawing board can be easily accomplished with CADD. For example, even for major changes redrawing is not necessary because diagrams can be manipulated in a number of ways to rearrange existing pieces of the drawing to fit the new shape. The basic capabilities include erasing, moving, copying and changing the appearance of drawing objects.
Introduction to three dimensions (3D)
Three-dimensional or 3D capabilities make it possible to draw pictorial views such as isometrics, oblique views and perspectives. Views drawn using CADD have a number of advantages compared with views drawn on a drawing board. The views drawn with CADD are very accurate and provide a great deal of flexibility in terms of editing and display.
Models can be rotated on the screen, displaying views from different angles. Designers often use 3D to visualize designs and to make presentations. It helps them understand how an object will appear from different angles. Drawings can be further enhanced using additional rendering programmes.
There are two distinct ways to draw 3D views with CADD. Views can be drawn using simple 2D functions or using CADDï¿½s special 3D functions. 2D functions can be used to draw views just as on a drawing board. A view can be drawn using lines, arcs, or other 2D objects. This is the quickest method to draw simple isometric and oblique views. However, a view created in this way is static, just like a view created on a drawing board.
If the object has to be viewed from a different angle, the plan has to be drawn again from the beginning. CADD provides special 3D functions for the creation of 3D drawings that are true representations of an actual model. These drawings can be viewed from any angle, just like a physical model, and that is why 3D CADD drawings are called 3D models.