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Figures 7-2 and 7-3 show a window box and a crossing box in action.
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Pick point 2
A window selection box, drawn left to right, selects only objects completely within the box.
Pick point 1
You can mix and match selecting individual objects, specifying a window box, and specifying a crossing box. Each selection adds to the current selection set, allowing you to build up an enormously complicated selection of objects and then operate on them with one or more editing commands.
You can press the Shift key in combination with any of the three standard selection modes — single object, window box, and crossing box — to remove already selected objects from the selection set. This feature is especially useful when you’re building a selection set in a crowded drawing; you can select a big batch of objects by using Window or Crossing, and then hold down the Shift key while selecting to remove the objects that you want to exclude from the editing operation.
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A crossing selection box, drawn right to left, selects objects that are completely or partially within the box.
When you edit in command-first mode, you have all the selection options described in the previous section — single object, window box, and crossing box — plus a slew of others. If you type ? and press Enter at any Select objects prompt, AutoCAD lists all the selection options at the command line.
Group/ Add/Remove/Multiple/Previous/Undo/AUto/ SIngle/SUbobject/Object
Subobject and Object are new selection objects in AutoCAD 2007 (but not AutoCAD LT), but they apply specifically to 3D solids. For more information on working in 3D, see Chapter 9.
Pick point 2
Pick point 1
166 Part II: Let There Be Lines
Pressing ? at a Select objects prompt has no impact on the dynamic input crosshairs display. You can see the options if you press the F2 key, but that takes a lot more screen space than the command line window. If your command line area is not visible, type COMMANDLINE and press Enter, or use the Ctrl+9 key combination to turn it on.
Table 7-1 summarizes the most useful command-first selection options.
Table 7-1 Some Useful Command-First Selection Options
Window All objects within a rectangle that you specify by picking two points
Last The last object you drew that's still visible in the drawing area
Crossing All objects within or crossing a rectangle that you specify by picking two points
ALL All objects on layers that aren't frozen or locked, and that are in the current space (model space or paper space)
Fence All objects touching an imaginary polyline whose vertices you specify by picking points
WPolygon All objects within a polygonal area whose corners you specify by picking points
CPolygon All objects within or crossing a polygonal area whose corners you specify by picking points
Previous The previous selection set that you specified
To use any of the command-first selection options at the Select objects prompt, type the uppercase letters corresponding to the option and press Enter. After you’re finished selecting objects, you must press Enter again to tell AutoCAD that you’ve finished selecting objects and want to start the editing operation.
AutoCAD’s Selection preview features (new in AutoCAD 2006) remove any doubt about which objects you’re selecting. Rollover highlighting displays individual objects with a thick dashed lineweight as the crosshairs are moved over them. Area selection displays a transparent, colored highlight over multiple selections using window and crossing options. You can enable and disable both features on the Selection tab of the Options dialog box (see Figure 7-1).
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The following example demonstrates how to use the ERASE (E) command in command-first mode with several different selection options. The selection techniques used in this example apply to most AutoCAD editing commands.
1. Press Esc to make sure that no command is active and no objects are selected.
If any objects are selected when you start an editing command, the command, in most cases, will operate on those objects (selection-first editing) instead of prompting you to select objects (command-first editing). For the reasons that we describe earlier in this chapter, you should use the command-first editing style until you’re thoroughly familiar with it. Later, you can experiment with selection-first editing if you like. (Just reverse the sequence of commanding and selecting that we describe in this chapter.)
2. Click the Erase button on the Modify toolbar.
AutoCAD displays the Select objects prompt at the command line and the dynamic input tooltip.
3. Select two or three individual objects by clicking each one.
AutoCAD adds each object to the selection set. All the objects you select remain ghosted. AutoCAD displays the Select objects prompt.