Recovering from Unintentional Edits

Often when you’re using AutoCAD, you will need to go back to an earlier state of the drawing either by disposing of unneeded objects or restoring removed objects. The following sections discuss methods of recovering edits made to the current drawing.

Recovering Erased Objects

You can use the ERASE command to remove selected objects from a drawing. The ERASE command is found on both the Modify toolbar and the Modify menu. After selecting the desired objects, press the Enter key or the spacebar or right-click to end the general selection process. Because the ERASE command does not require any further information, the objects are then erased.

If you erase any objects by accident, you can undo the ERASE command. A specific command also can be used to retrieve the most recent selection of erased objects. Use the OOPS command whenever you want to unerase objects removed with the last ERASE command without affecting any other edits you’ve performed since the last ERASE command.

Undoing Changes

In previous sections, you learned to use the Undo tool on the Standard toolbar to issue the U command that will undo the effects of the last command. A more powerful version of the U command also exists: the UNDO command, issued by typing UNDO at the Command: prompt. The following list outlines the undo options and their functions:

• Number. With Undo, you can specify the number of commands to be undone by typing the number of commands you want to undo at the prompt. The REDO command undoes the effects of the UNDO command regardless of the number of options you specify within a single undo.

• Auto. Auto enables you to undo a complete menu selection as a single command sequence (this is also reversible with a single U command keystroke). Undo Auto inserts an Undo Begin at the start of each menu section—if a menu section is not already active—and inserts an Undo End upon exiting from the menu section.

• Control. Using Control, you can limit AutoCAD’s ability to undo commands to just one command. Typically, the only time you must deal with the options available through Control is when you are critically short of drive space (because keeping track of commands takes up hard drive space). In such situations, it is better to allocate more free drive space than to limit AutoCAD’s ability to undo commands.

• Begin/End. The Begin option begins the process of grouping a series of commands. All commands following that option become part of the group until you use the End option to close the group. UNDO and U both treat grouped commands as a single operation.

• Mark/Back. Use the Mark option of the UNDO command to mark (much like a bookmark) a place in the Undo information file maintained by AutoCAD. Later, during the same drawing session, you can use the Back option to undo all commands issued since the last Mark option was specified.

  In addition to undoing the commands, the Back option also removes the last mark. You can issue the Mark option as many times as you want during a drawing session to place multiple “bookmarks” throughout your drawing process.

Understanding the functionality of the UNDO command can be difficult. The following exercise demonstrates the power of the UNDO command.

Exercise 10.2 Using UNDO to Recover Unintentional Edits

1.	Open CHAP10-1.dwg from the CD if it’s not open from the previous exercise. Choose Named Views from the View pull-down menu. Then select the view named OFFICE-D, click the Set Current button in the View Control dialog box, and click OK.
2.	Use the LINE command to draw four lines from through as shown in Figure 10.9. Press Enter to exit the LINE command. Figure 10.9. The office area with chairs and desks.
3.	Execute the UNDO command by typing UNDO at the command line. Then type M for Mark and press Enter. This puts a marker in the AutoCAD system for use later.
4.	Using the LINE command again, put an X in by picking points to . Press Enter twice, then pick and . Then press Enter to exit the command.
5.	Reissue the UNDO command, type B for the Back option, then press Enter. This removes the X series of lines. Notice the following command prompt: LINE LINE Mark encountered This indicates that two LINE commands were undone and were followed by an UNDO Mark hit. At this point, the Undo sequence stops.
6.	Now type REDO and press Enter to restore the X objects. The two lines reappear.
7.	Using the UNDO command again, type 1 and press Enter. The last line drawn disappears. This numbering option of the UNDO command allows you to go back a specified number of steps.
8.	Use the UNDO command once more. This time type 2 and press Enter. Only the last line disappears and the note Mark encountered appears. Even though you specified two steps back, AutoCAD halted when it reached an undo marker.
9.	Use the UNDO command again, type 1 , and press Enter. The four lines around the chairs disappear, and your drawing is restored to its original state. Leave this drawing open for the following exercise.

If the objects you have created are not correct, it’s often a better solution to change the appearance of these objects than to erase and re-create them. The following section covers various methods of resizing drawing objects.