Chapter 11: Edit for Credit 219

Figure 11-1: Choosing command options from the Dynamic Input menu.

As we describe in Chapter 7, maintaining precision when you draw and edit is crucial to good CAD work. If you’ve used a drawing program and are accustomed to moving, stretching, and otherwise editing objects by eye, you’ll need to suppress that habit when you edit in AutoCAD. Nothing ruins a drawing faster than eyeball editing, in which you shove objects around until they look okay, without worrying about precise distances and points.

Users of Windows Paint and other bitmap drawing programs will be familiar with the concept of “nudging” — selecting some objects and using the arrow keys to move them a certain number of pixels horizontally or vertically. For better or worse, AutoCAD has joined the nudging party. You can move objects a pixel’s-worth this way or that by holding down Ctrl and pressing an arrow key. When working with AutoCAD, you should always use tried-and-true precision drafting techniques, and moving objects by the pixel instead of by realworld units is the opposite of precise. It might be okay to move a piece of text by nudging it, but you should never move actual drawing geometry that way.

The Big Three: Move, Copy, and Stretch

Moving, copying, and stretching are, for many drafters, the three most common editing operations. AutoCAD obliges this need with the MOVE, COPY, and STRETCH commands.

Base points and displacements

The MOVE, COPY, and STRETCH commands all require that you specify how far and in what direction you want the objects to be moved, copied, or stretched. After you’ve started the command and selected the objects to be edited, AutoCAD prompts you for two pieces of information:

Specify base point or [Displacement] <Displacement>:

Specify second point or <use first point as displacement>:

www.it-ebooks.info

220 Part II: Let There Be Lines

In a subtle way, these prompts say that two possible methods exist for you to specify how far and in what direction you want the objects copied, moved, or stretched:

The most common way is to pick or type the coordinates of two points that define a displacement vector. AutoCAD calls these points the base point and the second point. Imagine an arrow pointing from the base point to the second point — that arrow defines how far, and in what direction, the objects are copied, moved, or stretched.

The other way is to type an X,Y pair of numbers that represents a distance rather than a point. This distance is the absolute displacement that you want to copy, move, or stretch the objects.

How does AutoCAD know whether your response to the first prompt is a base point or a displacement? It depends on how you respond to the second prompt. It might seem a little confusing at first, but it’s actually quite simple. First, you pick a point onscreen or enter coordinates at the Base point prompt. Next, there are a couple of possibilities:

If you then pick or type the coordinates of a point at the second point prompt, AutoCAD says to itself, “Aha — displacement vector!,” and moves the objects according to the imaginary arrow pointing from the base point to the second point.

If you press Enter at the second prompt (without having typed anything), AutoCAD says, “Aha — displacement distance,” and uses the X,Y pair of numbers that you typed at the first prompt as an absolute displacement distance.

What makes this displacement business interesting is that AutoCAD lets you pick a point at the first prompt and then press Enter at the second prompt. AutoCAD still says, “Aha — displacement distance,” but now it treats the coordinates of the point you picked as an absolute distance relative to the drawing’s origin. If the point you picked has relatively large coordinates, the objects can be moved to somewhere northeast of Greenland. You probably won’t see where they’ve gone because you’re zoomed into part of your normal drawing area, and so it just seems like the objects have vanished!

In short, be careful when you press Enter during the MOVE, COPY, and STRETCH commands. Press Enter in response to the second prompt only if you want AutoCAD to use your response to the first prompt as an absolute displacement. If you make a mistake, click Undo or press Ctrl+Z to back up and try again. You can use Zoom Extents (described in Chapter 12) to look for objects that have flown off into space.

Move

The following steps demonstrate command-first editing with the MOVE command, using the base point method of indicating how far and in what

www.it-ebooks.info

Chapter 11: Edit for Credit 221

direction to move the selected objects. This procedure also gives detailed recommendations on how to use precision techniques when you edit.

1.Press Esc to make sure that no command is active and no objects are selected.

2.Click the Move button on the Modify panel of the Home tab.

The command line displays the Select objects prompt.

3.Select one or more objects.

You can use any of the object selection techniques described in the “Perfecting Selecting” section in Chapter 10.

4.Press Enter when you’re finished selecting objects.

AutoCAD displays the following prompt:

Specify base point or [Displacement] <Displacement>:

5.Specify a base point by clicking a point or typing coordinates.

This point serves as the tail end of your imaginary arrow that indicates how far and in what direction you want the objects moved. After you pick a base point, it’s fairly easy to see what’s going on because

AutoCAD displays a temporary image of the object that moves around as you move the crosshairs. Figure 11-2 shows what the screen looks like.

Figure 11-2: Dragging objects in the middle of the MOVE command.

Specify a base point somewhere on or near the object(s) that you’re moving. You can use an object snap mode to choose a point exactly on one of the objects.

AutoCAD displays the following prompt:

Specify second point or <use first point as displacement>:

6. Specify the second point by clicking a point or typing coordinates.

www.it-ebooks.info

222 Part II: Let There Be Lines

The second point serves as the arrow end of your imaginary displacement arrow. After you specify the second point, AutoCAD moves the objects.

Don’t press Enter alone at this prompt! If you do, AutoCAD treats the X,Y coordinates of the first point you picked as an absolute displacement, and the objects fly off unpredictably. I repeat: Don’t press Enter alone at this prompt! As indicated in the previous warning, pressing Enter without picking a point or typing coordinates at this prompt is one of the most common errors new AutoCAD users make, and it can really pollute your drawing with unwanted objects.

These are the common precision techniques for specifying the second point:

Use an object snap mode to pick a second point exactly on another object in the drawing.

Type a relative or polar coordinate, as described in Chapter 7. For example, if you type @6,2, AutoCAD moves the objects 6 units to the right and 2 units up. If you type @3<45, AutoCAD moves the objects 3 units at an angle of 45 degrees.

Use direct distance entry to move objects in an orthogonal or polar-tracking direction. See Chapter 7 for instructions.

Copy

The COPY command works almost identically to the MOVE command, except that AutoCAD leaves the selected objects in place and makes new copies of them in the new location.

The COPY command creates multiple copies by default. If you want only one copy, press Enter after placing it in the drawing. Choosing mOde at the command prompt or the Dynamic Input options list lets you switch between making a single copy and multiple copies. If you mostly make multiple copies or mostly make single copies, you’ll appreciate being able to change the default setting.

The COPY command includes an Array option. In addition to plunking copied objects down just anywhere, typing A to choose the Array option lets you specify spacing for an evenly laid-out linear array. That’s good if you just want a single row of copies, but the ARRAY command (which we describe later in this chapter and in Chapter 18) is required to create rows and columns or circular patterns of copied objects.

The COPY command includes an Undo option with which you can roll back multiple copies within a single COPY operation.

www.it-ebooks.info