CREATE 2D BASIC DRAWING

BDA 10102 COMPUTER AIDED DESIGN

Lecturer’s name:1. Ashari bin Kasmin2. Abd Khalil bin Abd Rahim3. Muhammad Aimullah bin Abdullah4. Helmy bin Mustafa El Bakri5. Muhammad bin Zulkipli

After completing this chapter, you will be able to:

• Identify the default coordinate system and use dynamic input, direct distance, and shortcut menus.

• Use the Line, Circle, Arc, Erase, Rectangle, and Polygon commands to create and erase geometry in the drawing.

• Use object snaps to accurately place and create objects in the drawing.

• Activate and use the Polar Tracking and PolarSnap modes to more accurately create geometry at different angles in the drawing.

• Explain, enable, and use object snap tracking to position geometry in the drawing.

Objectives

Inputting Data

The following image illustrates how to use the Dynamic Input interface to draw a 10mm line at 30 degrees.

Every drawing action requires some form of data input. Regardless of the types of geometry you create, you are constantly inputting data in one form or another.

•Command options appear on the command line. The capitalized letter(s) represents the letter(s) you enter to use that option. You are not required to enter the letter(s) as a capital letter.

•Options for the command appear within [...] brackets. If there is a default option for the command, it appears within <...> brackets. To use the default option, press ENTER.

Command Line Options

The Dynamic Input interface is a way of entering data dynamically. Rather than entering data on the command line, which is generally positioned at the bottom of the screen, you can use the Dynamic Input interface for heads-up design, entering command information on screen at the cursor location.

Dynamic Input

1. Tooltip2. Coordinate, Length,

or Angle input fields3. Down Arrow.4. Dynamic Input

Menu

Every object you draw is placed in either the world

coordinate system (WCS) or a user coordinate

system (UCS). When you create 2D geometry, data

input is ultimately passed to the software in the

form of Cartesian (x,y) or polar coordinates

(distance, angle). You can either manually enter

these coordinates or infer them by picking a point

in the drawing window.

Coordinate System

The following image illustrates a line drawn from the origin of the coordinate system 0,0 with its endpoint at the coordinate 4,6.

Cartesian Coordinate Systems

To specify a Cartesian coordinate, type the X and Y coordinates and press ENTER. Example: 4,6 where X is equal to the distance from the origin along the X axis and Y is equal to the distance from the origin along the Y axis.

A polar coordinate is a point in the coordinate system that is determined by a distance and an angle.

The following illustration shows a line drawn from the origin of the coordinate system with a length of 7 units and an angle of 45 degrees.

Polar Coordinate Systems

To specify a polar coordinate, type the distance < angle, example 5<45, where Distance equals the distance travelled from the specified origin point and Angle equals the angle from the X axis.

Polar AngleThe default polar angle is measured counter clockwise from the zero angle position. The default zero angle is in the East compass direction.

An absolute coordinate represents a specific point in the current coordinate system relative to the origin point (0,0). To enter an absolute coordinate, type the values as a Cartesian coordinate (x,y) or Polar coordinate (distance angle).

Absolute and Relative Coordinate Examples:

Absolute and Relative Coordinate System

The following lines could have been drawn using Cartesian or Polar coordinates. Assuming the start point at the red arrow, the command line input for relative Cartesian or Polar coordinates would be as follows:

Point 2: @4,0 or @4<0

Point 3: @0,2 or @2<90

Point 4: @-1,0 or @1<180

Example of Cartesian or Polar Coordinate Input

All drawings consist of basic objects that you

create using basic commands. In this lesson,

you learn how to create objects such as lines,

circles, arcs, rectangles, and polygons. You also

learn how to use the Erase command to erase

objects.

Creating Basic Objects

The following illustration shows a line segment being drawn using the dynamic input interface to specify the length (1) and angle (2) of the segment.

Line Command

Line options can be selected from the shortcut menu or typed at the Command line (L).

In the following image, the circle centre point is selected and you are prompted to specify a radius.

Circle Command

Circle options can be selected from the shortcut menu or typed at the Command line (C).

The following illustration represents an arc being created through three points.

Arc Command

Arc options can be selected from the shortcut menu or typed at the Command line (Arc).

This illustration shows a rectangle with the point used to create it specified.

Rectangle Command

Use the Polygon command to create regular polygon geometry by specifying the center point and radius of an imaginary circle, or the start point and endpoint of one of the polygon edges.

Polygon Command

Object SnapEvery object you create has various selectable points that you can use to position other objects. Every time you create an object you are required to specify a point or location. It is critical that these points be defined accurately if you expect your drawing to be accurate. The following are the object snap modes available in AutoCAD.

• ENDpoint• MIDpoint• INTersection• APParent

Intersection• CENter• QUAdrant• TANgent

• EXTension• PERpendicular• PARallel• INSert• NODe• NEAest• From

The ENDpoint Object Snap mode snaps to the closest endpoint of a line or an arc. To use this Object Snap mode, select the Endpoint button, and move the cursor (crosshairs) anywhere close to the endpoint of the object. The marker will be displayed at the endpoint; click to specify that point. For figure, invoke the LINE command from the Draw toolbar. The following is the prompt sequence:

ENDpoint Object Snap mode

Specify first point: Select the Endpoint button from the Object Snap toolbar.

_endp of Move the crosshair and select the arc.

Specify next point or [Undo]: Select the endpoint of the line.

• Endpoint

The MIDpoint Object Snap mode snaps to the midpoint of a line or an arc. To use this Object Snap mode, select Midpoint osnap and select the object anywhere. AutoCAD will grab the midpoint of the object. For figure, invoke the LINE command from the Draw toolbar. The following is the prompt sequence.

MIDpoint Object Snap mode

Specify first point: Select the starting point of the line.

Specify next point or [Undo]: Choose the Snap to Midpoint button from the Object Snap toolbar.

_mid of Move the cursor and select the original line.

• Midpoint

The CENter Object Snap mode allows you to snap to the center point of an ellipse, circle, or arc. For figure, invoke the LINE command from the Draw toolbar. The following is the prompt sequence:

Specify first point: Choose the Snap to Center button from the Object Snap toolbar.

_cen of Move the cursor and select the circle.

Specify next point or [Undo]: Select the endpoint of the line.

CENter Object Snap mode

For figure, invoke the LINE command from the Draw toolbar. The following is the prompt sequence:

Specify first point: Select the starting point of the line.

Specify next point or [Undo]: Choose the Snap to Tangent button from the Object Snap toolbar.

_tan to Move the cursor and select the circle.

Specify next point or [Undo]: Select the endpoint of the line (tangent of the circle).

TANgent Object Snap mode

• Center

• Tangent

The QUAdrant Object Snap mode is used when you need to snap to a quadrant point of an ellipse, arc, or circle. A circle has four quadrants, and each quadrant subtends an angle of 90-degree. If the circle is inserted as a block, that is rotated, the quadrant points are also rotated by the same amount, see figures.

To use this object snap, position the cursor on the circle or arc closest to the desired quadrant, see figure.

Quadrants in a rotated circle

Location of circle quadrants

QUAdrant object snap mode

• Quadrant

The INTersection Object Snap mode is used to snap to a point where two or more lines, circles, ellipses, or arcs intersect. For figure, invoke the LINE command. The prompt sequence is given next.

INTersection Object Snap mode

Specify first point: Choose the Snap to Intersection button from the Object Snap toolbar.

_ int of Position the cursor near the intersection and select it.

Specify next point or [Undo]: Select the endpoint of the line.

After selecting the Intersection object snap, if your cursor is close to an object and not close to an actual intersection, the intersection marker displays ellipses [...] with it. This indicates an extended intersection. This mode selects extended or visual intersections of lines, arcs, circles, or ellipses (figure). Extended Intersection

Object Snap mode

• Intersection

The PERpendicular Object Snap mode is used to draw a line perpendicular to or from another line, or normal to or from an arc or circle, or to an ellipse. The prompt sequence to draw a line perpendicular to a given line (figure) is given next.

Specify first point: Select the starting point of the line.

Specify next point or [Undo]: Choose the Snap to Perpendicular button from the Object Snap toolbar.

_per to Select the line on which you want to draw perpendicular.

The prompt sequence for drawing a line perpendicular from a given line (figure) is given next.

Specify first point: Choose the Snap to Perpendicular button from the Object Snap toolbar.

_per to Select the line on which you want to draw perpendicular.

Specify next point or [Undo]: Select the endpoint of the line.

PERpendicular Object Snap mode

Selecting the perpendicular snap first

• Perpendicular

The NEArest Object Snap mode selects a point on an object (line, arc, circle, or ellipse) that is visually closest to the graphics cursor (crosshairs). To use this mode, enter the command, and then choose the Nearest object snap. Move the crosshairs near the intended point on the object so as to display the marker at the desired point and then select the object. For figure, invoke the LINE command from the Draw toolbar. The following is the prompt sequence: NEArest Object Snap mode

Specify first point: Choose the Snap to Nearest button from the Object Snap toolbar.

_nea to Select a point near an existing object.

Specify next point or [Undo]: Select endpoint of the line.

• Nearest

The INSert Object Snap mode is used to snap to the insertion point of a text, shape, block, attribute, or attribute definition. In figure, the text WELCOME is left-justified and the text AutoCAD is center-justified. The point with respect to which the text is justified is the insertion point of that text string. If you want to snap to these insertion points or the insertion point of a block, you must use the INSert Object Snap mode. Invoke the LINE command and following is the prompt sequence:

Specify first point: Choose the Snap to Insert button from the Object Snap toolbar.

_ins of Select WELCOME text.

Specify next point or [Undo]: Choose the Snap to Insert button from the Object Snap toolbar.

_ins of Select the block.

Specify next point or [Undo]: Choose the Snap to Insert button from the Object Snap toolbar.

_ins of Select AutoCAD text.

INSert Object Snap mode

• Insert

Units represent the baseline of all the geometry that you create in your drawing. It is up to you to determine what unit of measurement will be used in your drawing.

About Units & Setting

END OF

LESSON 2