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Object snap tracking: This feature extends running object snaps so that you can locate points based on more than one object snap point. For example, you can pick a point at the center of a square by tracking to the midpoints of two perpendicular sides.
Polar tracking: When you turn on polar tracking, the crosshairs jump to increments of the angle you selected. When the crosshairs jump, a tooltip label starting with Polar: appears. Right-click the POLAR button on the status bar and choose the Settings option to display the Polar Tracking tab on the Drafting Settings dialog box. Select an angle from the Increment Angle drop-down list and then click OK. Click the POLAR button on the status bar or press F10 to toggle polar tracking mode off and on.
Polar snap: You can force polar tracking to jump to specific incremental distances along the tracking angles by changing the snap type from grid snap to polar snap. For example, if you turn on polar tracking and set it to 45 degrees and turn on polar snap and set it to 2 units, polar tracking
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jumps to points that are at angle increments of 45 degrees and distance increments of 2 units from the previous point. Polar snap has a similar effect on object snap tracking.
To activate polar snap, follow these steps:
1. Right-click the SNAP button on the status bar.
2. Choose the Settings option.
The Snap and Grid tab on the Drafting Settings dialog box appears.
3. Click the Polar Snap radio button, type a distance in the Polar Distance text box, and then click OK.
When you want to return to ordinary rectangular snap, as described at the beginning of this list, select the Grid Snap radio button in the Drafting Settings dialog box.
^ Temporary overrides: Settings such as SNAP, ORTHO, and POLAR remain on until you turn them off. You can also use temporary overrides, which last only as long as you hold down their key or key combination. For example, with ortho turned off, holding down the Shift key puts AutoCAD into a temporary ortho mode for as long as you press Shift. For additional information, look up “temporary override keys” in the online help system.
If you’re new to AutoCAD, its wide range of precision tools probably seems overwhelming at this point. Rest assured that there’s more than one way to skin a cat precisely (with cats, accuracy is unimportant), and not everyone needs to understand all the ways. You can make perfectly precise drawings with a subset of AutoCAD’s precision tools. We recommend these steps:
1. Get comfortable with typing coordinates, ortho mode, direct distance entry, and object snap overrides.
2. Become familiar with running object snaps and try Snap mode.
3. After you have all these precision features under your belt, feel free to experiment with polar tracking, polar snap, and object snap tracking.
It’s easy to confuse the names of the snap and object snap (osnap) features. Remember that snap limits the crosshairs to locations whose coordinates are multiples of the current snap spacing. Object snap (osnap) enables you to grab points on existing objects, whether those points happen to correspond with the snap spacing or not.
Where to Draw the Line
In This Chapter
^ Drawing with the AutoCAD drawing commands ^ Lining up for lines and polylines ^ Closing up with rectangles and polygons ^ Rounding the curves with circles, arcs, splines, and clouds ^ Dabbling in ellipses and donuts ^ Making your points
Лs you probably remember from your crayon and coloring book days, drawing stuff is fun. CAD imposes a little more discipline, but drawing AutoCAD objects is still fun. In computer-aided drafting, you usually start by drawing geometry — shapes such as lines, circles, rectangles, and so on — that represent the real-world object that you’re documenting. This chapter shows you how to draw geometry.
After you’ve created some geometry, you’ll probably need to add some dimensions, text, and hatching, but those elements come later (in Part III of this book). Your first task is to get the geometry right; then you can worry about labeling things.
Drawing geometry properly in AutoCAD depends on paying attention to object properties and the precision of the points that you specify to create the objects. We cover these matters in Chapter 5, so if you eagerly jumped to this chapter to get right to the fun stuff, take a moment to review that chapter first.
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Introducing the AutoCAD Drawing Commands
For descriptive purposes, this chapter divides the drawing commands into three groups:
Straight lines and objects composed of straight lines
Table 6-1 offers an overview of most of the drawing commands in AutoCAD, without the 3D-related commands. It describes the commands’ major options and shows you how to access them from the command line, the Draw menu, and the Draw toolbar. (Don’t worry if not all the terms in the table are familiar to you; they become clear as you read through the chapter and use the commands.)