AutoCAD & AutoCAD LT All-In-One Desk Reference For Dummies (2006)

112 Working with Object Snap Tracking Mode

The prompt changes to

.X of (need yz):

7.Move the crosshairs over a vertical side of the rectangle and click when you see the Midpoint object-snap marker.

AutoCAD locates the center point of the circle at a new point generated from the x coordinate of the first picked point, and the y coordinate of the second.

Working with Object Snap Tracking Mode

No, OTRACK is not the name of the Irish railway system. Sure and begorrah, OTRACK is much more useful than that. OTRACK is short for object-snap tracking, an AutoCAD feature that lets you locate new points based on objectsnap points on existing objects.

Object snap tracking automates the point-filter process we described earlier. For example, here’s how you’d use object-snap tracking to place a circle in the exact center of a rectangle:

1.Open a drawing containing a rectangular area in which you want to draw a circle, or draw a rectangle in a blank area of the screen.

2.Right-click the OTRACK button on the status bar to display the Drafting Settings dialog box, and make sure that Midpoint object snap is selected.

You can also right-click the OSNAP button to display the Object Snap tab of the Drafting Settings dialog box.

3.In the Drafting Settings dialog box, select the Object Snap On and Object Snap Tracking On checkboxes, and then click OK.

4.Start the CIRCLE command.

AutoCAD prompts:

_circle Specify center point for circle or [3P/2P/Ttr (tan tan radius)]:

5.Move the crosshairs to the middle of a horizontal side of the rectangle.

The Midpoint object-snap marker appears.

6.Rest the crosshairs over the object-snap marker for a moment, but don’t click yet.

Working with Object Snap Tracking Mode 113

When you move the mouse, you should see a tracking vector passing through the object-snap marker.

7.Without clicking, move the crosshairs to the middle of a vertical side of the rectangle.

8.When the object-snap marker appears, rest the crosshairs over it for a moment.

Now when you move the mouse, you should see two tracking vectors, one running through each of the midpoints.

9.Move the mouse until the two tracking vectors are aligned vertically and horizontally (see Figure 6-7), and then click to set the center point of the circle.

If DYNamic mode is enabled, you also get confirmation that you’re on the money in the dynamic input tooltip.

Figure 6-7:

Finding the “center” of a square using object-snap tracking.

Although object-snap tracking has been part of the full version of AutoCAD for several releases now, it’s just been introduced to AutoCAD LT 2007. It’s not included in AutoCAD LT 2006 and earlier versions.

Book I

Chapter 6

Tools Precision

114 Book I: AutoCAD Basics

Book II

2D Drafting

Contents at a Glance
Chapter 1: Drawing Objects ..............................................................................................	117
Chapter 2: Modifying Objects ............................................................................................	143
Chapter 3: Managing Views................................................................................................	171

Chapter 1: Drawing Objects

In This Chapter

Input methods

Using drawing tools

Creating primitive objects

Understanding construction objects

Drawing complex objects

Welcome to Book II. It’s time to get primitive! No, we’re not asking you to move into a tree in the backyard and howl at the moon. In this

chapter, we introduce AutoCAD’s primitive objects and the drawing commands for creating them. Primitive objects include geometric entities like lines, arcs, circles, and points.

After we explore the primitive heart of AutoCAD, we look at some of its more complex object-creation tools. These include polylines, multilines (double lines if you’re using AutoCAD LT), and some obscure entities like traces and 2D solids.

As we explain in Book I, you can interact with AutoCAD in several ways. You can start most drawing commands from the Draw toolbar or the Draw menu, or by typing the command name (or its short-form alias) at the keyboard. In nearly all cases, using any of these methods to start a command initiates a dialog with AutoCAD.

Locating and Using the Drawing Tools

Table 1-1 tells you where to find all the drawing commands AutoCAD provides, as well as what you can do with these commands. We don’t cover the commands in this order; just think of this table as a handy reference chart. In the interests of fairness and democracy, Table 1-1 lists commands in alphabetical order by command name, not by popularity or frequency of use. LINE, ARC, and CIRCLE are the most frequently used commands.

118 Locating and Using the Drawing Tools

	Table 1-1			AutoCAD’s 2D Drawing Tools
	Icon		Draw	Draw	Command	Alias	Function
			Toolbar	Menu	Name
			Arc	Arc	ARC	A	Draws circular arc
							objects.
			—	Block, Define	ATTDEF	ATT	Defines attributes to
				Attributes			be included in block
							definition. Attributes
							are covered in Book VI.
			Make	Block,	BLOCK	B	Defines a block from
			Block	Make			drawing objects. Blocks
							are covered in Book VI.
			—	Boundary	BOUNDARY	BO	Creates polyline or
							region from edges of a
							closed area. For more
							on Boundary, see
							Book III.
			Circle	Circle	CIRCLE	C	Draws circle objects.
			—	Double Line	DLINE	DL	Draws double parallel
							lines (AutoCAD LT only).
			—	Donut	DONUT	DO	Draws circular polyline
							object specifying inside
							and outside diameter.
			Ellipse	Ellipse	ELLIPSE	EL	Draws ellipse objects.
			Gradient	Gradient	GRADIENT	GD	Applies gradient fill
							pattern to closed
							areas. Gradients are
							covered in Book III.
			Hatch	Hatch	HATCH	H	Applies solid or regular
							pattern to closed
							areas. Hatches are
							covered in Book III.
			Line	Line	LINE	L	Draws straight line
							objects between two
							points.
			—	Multiline	MLINE	ML	Draws multiple parallel
							lines (AutoCAD only).
			Multiline	Text, Multiline	MTEXT	MT	Draws multi-line anno-
			Text	Text			tation text objects. Text
							is covered in Book III.

(continued)

Locating and Using the Drawing Tools 119

	Icon	Draw	Draw	Command	Alias	Function
		Toolbar	Menu	Name
		Polyline	Polyline	PLINE	PL	Draws connected
						linear or arc segment
						objects.
		Point	Point	POINT	PO	Draws point objects.
		Polygon	Polygon	POLYGON	POL	Draws regular closed
						polygonal polylines.
		Ray	Ray	RAY	—	Draws infinite-length
						construction line start-
						ing from single point.
		Rectangle	Rectangle	RECTANG	REC	Draws closed rectan-
						gular polyline objects.
		Region	Region	REGION	REG	Creates a single closed
						object from nested
						objects.
		Revision	Revision	REVCLOUD	—	Draws revision clouds.
		Cloud	Cloud
		—	—	SKETCH	—	Draws freehand
						sketches as polylines
						or multiple line objects.
		—	—	SOLID	SO	Draws 3- or 4-sided
						solid-filled shapes. Not
						related to 3D solids.
		Spline	Spline	SPLINE	SPL	Draws freeform spline
						curve objects.
		Table	Table	TABLE	TB	Draws table objects
						specifying rows and
						columns. Tables are
						covered in Book III.
		—	—	TRACE	—	Draws single-segment
						lines with width.
		Construc-	Construc-	XLINE	XL	Draws infinite-length
		tion Line	tion Line			construction line
						through specified
						points.

Book II

Chapter 1

Objects Drawing

If a command can be executed only by typing its name (that is, it has no tool button or menu item), it’s not going to be used that frequently; SKETCH, SOLID, and TRACE all fall into this category.

120 Let’s Get Primitive

In this chapter, we’re not going to cover every single drawing command in extensive detail — that’s what the online Help system is for. The Command Reference has an alphabetical listing of every command and details about each command’s options. To access the Command Reference, choose Help Help or press the F1 key. Click the Contents tab, and then click the plus sign beside Command Reference.

Sometimes you have to dig pretty deep in the Help system for the last word on a command or feature. On many Help pages, there’s an almost invisible little blue hyperlink that says, “Display all hidden text on this page.” Remember it’s there and look for it!

Let’s Get Primitive

AutoCAD’s primitive object types are lines, circles, arcs, and points. Each of these object types takes very little geometric data to define it in the drawing database. A line is defined geometrically by its two endpoints, arcs and circles by their center points and radii, and points by a single set of coordinates.

In this section, we look at the four commands that create these four primitive object types. The commands are (surprise!) LINE, CIRCLE, ARC, and POINT.

Keeping to the straight and narrow

The LINE command creates a line object. In AutoCAD, a line object is a single entity drawn between two endpoints. You use the LINE command to draw straight lines from point to point to point. The LINE command continues prompting for points until you explicitly end the sequence by pressing Enter or Esc. Whichever method you choose to start the command, AutoCAD prompts as follows:

Command: LINE

Specify first point:

Pick a point on-screen, or use an object snap (see Book I for more information on using object snaps) to find a precise point on an existing object, or type a pair of x,y coordinates to locate the starting point of your line sequence. After you pick the first point, AutoCAD prompts:

Specify next point or [Undo]:

Specify the second and third points using the methods just described. If you make a mistake, or change your mind after you pick the second point, press U (for Undo) and press Enter to undraw the previous line segment. As you continue to add line segments, you can press U at any time to undo the last segment you added.

Let’s Get Primitive 121

Command options appear inside square brackets. To select a command option, type the uppercase letter in the option and press Enter.

Specify subsequent points in the same manner as the first points. After you pick the third point (that is, after you have two line segments), the command prompt changes once more:

Specify next point or [Close/Undo]:

There are now two options, Undo and Close. After you’ve drawn two line segments, you can create a closed shape by pressing C and pressing Enter. If you’re using dynamic input, you can select Close from the dynamic display (see Figure 1-1). This will end the line sequence at the original starting point. To end the sequence, press Enter or Esc or the spacebar, or right-click and choose Enter from the shortcut menu.

Figure 1-1:

Drawing lines dynamically.

In Book I, we talk about relative coordinates and how AutoCAD interprets the @ symbol as relative to the last point you picked. You can use the @ symbol by itself to tell AutoCAD you want to use the last point you picked on-screen or entered using coordinates. For example, if you enter @ at the Specify first point prompt, AutoCAD starts the line at the last point entered.

Going around in circles

Circles are pretty basic geometric elements, although you may not create them quite as often as you create arcs. We’re going to talk about circles before we talk about arcs because circles are simpler to draw. Even so, there are five ways to create circles — six, if you use the pull-down menu. Figure 1-2 shows the pull-down menu with all six options.

Book II

Chapter 1

Objects Drawing