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CADD PRIMER
Chapter 2: CADD Basics

Contents

About this Chapter
Key Terms in this Chapter
Components of a CADD Drawing
Beginning to Draw
The Point-Selection Menu
The Coordinate System
  • Cartesian Coordinates
  • Polar Coordinates
  • The Formats to Enter Coordinates
  • User-Defined Coordinate System
A Prototype CADD Drawing
What if You Made a Mistake
When to Save the Drawing or Quit
Automatic Data Saving Features
CADD Filing System
A Word about Data Security
Getting Help
AutoCAD, MicroStation & Cadkey Terms
About this Chapter This chapter provides an overview of CADD functions. It describes what various functions will accomplish, how they are organized into CADD menus and how to use them.

You will learn to use basic functions to draw lines or circles, enter text, etc. A brief exercise walks you through the use of these functions. You will also learn how to measure distances and how to locate exact points. This chapter illustrates how to use coordinate methods, such as absolute coordinates, relative coordinates and polar coordinates to measure distances.

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In addition, this chapter highlights important principles in setting up CADD drafting standards. It demonstrates how to set up a prototype CADD drawing for a quick start.
Finally, this chapter shows you how to save drawings and where to store them. In this section, you will learn about data saving functions and safety measures to prevent data loss.

Key Terms in this Chapter
 
Term
Description
Aperture Effective diameter of the cursor on the screen.
Cartesian coordinates A rectangular system of measurement to locate points in the drawing area.
Isometric A view in 3D geometry when viewing an object from the top at a 45° angle.
Object snaps A method for indicating point locations using existing drawing objects as a reference.
Origin point The 0,0 location of the coordinate system.
Polar coordinates A system to locate the points using an angle and distance.
Prototype drawing A template drawing that has a number of preset defaults.
User-defined coordinate system A mode of measurement that allows the user to set up a customized coordinate system.

Components of a CADD Drawing AutoCAD Forum

CADD drawings are created by drawing individual components (also called drawing objects or entities) of the drawing such as lines, arcs, dimensions and symbols. On a drawing board, you may not notice how many lines and arcs you need to complete a diagram, but with CADD you need to be specific. You need to specify exactly what you want to draw and how you want to draw it. Consider this scenario: drawing a square with rounded edges. Using a drawing board, you would quickly draw four lines and round off the edges with a template. Using CADD to draw the similar square, you will have to draw four lines and four arcs separately. You must specify where each line and arc starts, where it ends, the center point of the arc, the radius, etc.

CADD’s drawing functions are used to create each component of a drawing. Fig. 2.1 illustrates the basic drawing components of CADD. As shown, there are many different kinds of lines, arcs, circles, ellipses, symbols, text, dimensions pointers, polylines, borders and patterns. You can complete most of the drawings by using these components of CADD.

To draw any component of the drawing, you need to access a particular function from the Draw menu. There are separate functions to draw text, dimensions, patterns, symbols, and other elements of a drawing. To draw a symbol, such as an octagon, you don't need to draw each side one by one. The Symbol function allows you to instantly insert a symbol into the drawing. Similarly, when you need to draw hatch patterns, borders, or arrows, separate CADD functions enable you to do that.

Drawing a component is quite straightforward. When you enter a command, the corresponding menu displays a prompt that guides you through steps to take. To complete a task, you will need to enter data using the keyboard, make selections from sub-menus, and enter points with the help of a pointing device to indicate where you want to position a drawing component.

The Coordinate System The coordinate system is a method of locating points in the drawing area. It enables you to locate points by specifying distances from a fixed reference point. You can locate a point by giving its distance in the horizontal direction, vertical direction, measuring along an angle, etc.

The coordinate system is available when a function requires data input in the form of point locations. You may use it while drawing, editing or any time you need to locate a point. The most common coordinate systems are as follows:
 

  • Cartesian coordinates
  • Polar coordinates

  • Note:

    The method of entering coordinates varies from one program to another. For example, in AutoCAD, the coordinates can be entered directly in the command window with the keyboard. In MicroStation and Cadkey, special dialog boxes let you enter the coordinates.
     

    Cartesian Coordinates  
    Cartesian coordinates is a rectangular system of measurement that enables you to locate points with the help of horizontal and vertical coordinates. The horizontal values, called X-coordinates, are measured along the X-axis. The vertical values, called Y-coordinates, are measured along the Y-axis. The intersection of the X- and Y-axes is called the origin point, which represents the 0,0 location of the coordinate system.

    The positive X values are measured to the right and the positive Y values are measured above the origin point. The negative X and Y values are measured to the left and below. To enter a coordinate, you need to enter both the X and Y values separated by a comma (X, Y).

    Example: To locate a point two units to the right and one unit above the origin point, enter X = 2, Y = 1 or (2,1). Similarly, to locate a point two units to the left and one unit below, you need to enter X = -2, Y = -1 or (-2, -1). You can use fractions as needed to enter the exact coordinate values.
     

    Polar Coordinates  
    Polar coordinates allow you to define a point by specifying the distance and the direction from a given point. This mode of measurement is quite helpful in working with angles. To draw a line at an angle, you need to specify how long a line you want to draw and specify the angle.

    The Format to Enter Coordinates

    Cartesian or polar coordinate values can be entered in two formats:
     

  • Absolute
  • Relative

  • Absolute format is a way of measuring distances from a fixed reference location (origin point), which is the 0,0 location of the coordinate system. Consider this point to be stationary at all times. In some CADD programs this point remains visible at the left bottom corner of the drawing area, while in others it is invisible. You can use this point as a reference to measure any distance in the drawing. Absolute coordinates are primarily used to adjust the alignment of diagrams in a drawing, to align one drawing with another or to make plotting adjustments.

    Relative format is a way of measuring distances from the last point entered. All measurements are taken the same way as the absolute coordinates, with the only difference being that the relative coordinates are measured from the last point entered instead of the origin point. When a point is entered, it becomes the reference for entering the next point and so on. This mode of measurement is frequently used for drawing because it is always convenient to place the drawing components relative to each other rather than a fixed reference point.

    Note:

    Each CADD program uses its own annotations to enter absolute or relative coordinates. The task table located at the end of the chapter shows some examples from leading CADD programs.

    A Prototype CADD Drawing A CADD program is designed to meet the needs of a vast number of individuals. It comes with a number of options that can be customized. For example, architects, engineers and surveyors use different annotations to measure units and to draw dimensions. You may have a number of preferences regarding a specific style of text, standard sheet sizes, names of layers, symbol styles, borders, or line types to be used in a project.

    When you install a CADD program, it does not have any of the defaults set as per your requirements. You can create a prototype drawing and specify all the defaults that you would like to use. This prototype drawing acts as a template that can be used for all future projects.

    When you start a new drawing, you can specify the name of the prototype drawing and all the defaults are taken from this file. This gives you a drawing of a specified size, with border type and all the other defaults set in the prototype drawing. When you start working with CADD, it is better to follow a prototype drawing. It saves a significant amount of time in starting a drawing, because CADD sets everything for you. You are ready to draw instantly.

    Most programs allow you to create more than one prototype drawing and save them under different filenames. This is particularly helpful when you are working on several projects that require different drawing standards. Whenever you need to use a specific standard, you can specify the name of that prototype drawing and those defaults are activated.

    Refer to CADD PRIMER for further details.



    Note: CADD PRIMER is illustrated with more than 100 diagrams. The above diagram is an example from CADD PRIMER showing the basic components of a CAD drawing.

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