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Inside AutoCAD 14

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Basic Object Editing

by Francis Soen

Part of the normal drawing process involves modifying, or editing, what has already been drawn. Two broad classes of editing commands are available to you: editing commands that can be used on a variety of objects and editing commands that are designed for a specific type of object. This chapter concentrates on the general editing commands and processes, while Chapter 11, "Advanced Geometry Editing," concentrates on object-specific types of editing commands. This chapter discusses the following skills:

Editing Named Objects

AutoCAD objects fall into two expansive categories: named and unnamed objects. Named objects are items that you name when you create them--named objects are referred to by their assigned names. Examples of named objects include layers, block definitions, and text styles. Unnamed objects are objects such as lines, circles, and arcs that cannot be assigned names.

Named objects can be physical objects, such as blocks, that can be edited with multiple commands covered in this chapter. Named objects also can be non-physical objects, such as named views or User Coordinate Systems (UCSs), that can be edited only with the specific commands covered in this section. In this portion of the chapter, you will be introduced to the editing operations used to manipulate named objects.

Renaming Named Objects

Sometimes you need to rename a layer or a block because of changing conditions or simple typographic errors committed when you initially created the objects.

To rename a named object, you can use the Rename dialog box (see fig. 10.1), which is invoked by choosing Rename from the Format pull-down menu.

Figure 10.1 The Rename dialog box of DDRENAME can be used to rename a named object.

After you choose the type of named object to be renamed, a list of the existing objects of that type are displayed. You select the specific object to be renamed, type the new name in the text-edit box next to the Rename To button, and press the Rename To button to implement the name change.

NOTE: Layer 0 is the only layer that cannot be renamed, which accounts for why this layer is never displayed as part of the list of layers that can be renamed.

Deleting Named Objects

Sometimes you end up with unneeded layers or linetypes and want to delete the objects from the drawing.

The act of deleting a named object is referred to as purging the object. This action is performed with the PURGE command, which is invoked by choosing Purge from the Drawing Utilities submenu of the File menu. You can choose to purge all named objects or limit the command to a specific type of named object, such as text styles. Named objects that are not used, such as a layer with no objects drawn on it, are referred to as unreferenced objects. Only unreferenced objects can be purged from a drawing. Whenever PURGE finds a NAMED object suitable for deletion, you are asked to confirm the deletion prior to the object being deleted.

NOTE: Layer 0 can never be deleted, even if it is unreferenced.

Although saved Users Coordinate Systems, UCSs, views, and viewport configurations are named objects and can be renamed with the Rename dialog box, PURGE does not give you the option of deleting these types of objects. Instead, if you want to delete the objects, you must employ the command used to manage them. For example, you cannot use the PURGE command to delete a named view. Instead, you must use the Delete button of the View Control dialog box to delete a named view. Use DDUCS to delete UCSs and use VPORTS to delete named viewport configurations.

TIP: If you have many unreferenced objects to be purged, the PURGE command could prove to be annoying because the system asks you to confirm the deletion of each object before the deletion is actually processed. A quicker way to purge a drawing of all unreferenced objects (except saved UCSs, views, and viewport configurations) is to use the EXPORT command (see Chapter 27, "Publishing on the Web"). The EXPORT command enables you to create a new drawing file and specify the "*" wild-card character as the block name to be exported. The "*" option specifies both that the entire drawing should be exported to the new drawing file and that all unreferenced named objects should be purged from the new drawing. The name of the new drawing created can be the same as the current drawing. In this case, you essentially replace the current version of the drawing with a new purged version.

In the following exercise, you will purge an unreferenced layer and rename another.

PURGING AND RENAMING LAYERS

1. Open the drawing MODIFY.DWG. From the File menu, choose Drawing Utilities, Purge, and Layers. When prompted for layer names to purge, enter an *. When prompted for Verify each name to be purged?, enter Y. Purge the BORDER and 1FL_FURNITURE layers, but do not purge the CPU-PENTIUM layer.

2. Choose Rename from the Format menu, and choose Layer from the Named Objects list (see fig. 10.2). Then choose CHAIRS from the items list. Enter EXEC-CHAIRS in the Rename To text-edit box, and then click on the Rename To button. Click on the OK button to exit the Rename dialog box.

3. Save the drawing.

Figure 10.2 Renaming layer CHAIRS to EXEC-CHAIRS.

Modifying Named Objects

Some named objects, specifically text styles, dimension styles, and multiline styles, are also known as named styles. A style is really nothing more than a collection of settings that affects a particular type of object. In addition to being renamed and purged, named styles can be modified in other ways. Specific information on modifying each type of named style is discussed in detail in the various sections of this book that discuss defining and using the different objects. For example, Chapter 16, "Text Annotation," details the creation and subsequent modification of text styles.

The remainder of this chapter concentrates on commands that you use to edit the objects in your drawing such as lines, circles, and block insertions. Before you can learn to use specific editing commands, you must first lean how to select the objects you want to change, which is the subject of the next section.

Selecting Objects to Edit

When you edit objects, a variety of options exist when it comes to selecting objects for specific commands. Some commands, such as the DDEDIT command, prompt you to select a specific type of object or, as with the FILLET command, a specific number of objects. Other commands, such as the ERASE command, enable you to perform a general selection process that invites you to select as many different objects as you want using a variety of techniques. Any command, such as ERASE, that starts with the Select Objects: prompt enables you to use the general selection process, which is the topic of the next section.

Assembling a Selection Set

Many of the editing commands start by displaying the Select Objects: prompt. The Select Objects: prompt signals the beginning of the open process used to assemble a selection set. This process enables you to select the desired objects with a variety of methods, all of which are defined in the following list. Most of the selection options covered in the following list are invoked by typing a key letter or two at the Select Objects: prompt--the necessary key letters are capitalized in the option word itself. The general selection process is open-ended, which means that you can invoke any of the options listed as many times as you want and in any order that you want. All selected objects are highlighted on the screen as a visual confirmation. The highlighting of objects is enabled (default setting) with the Highlight option in the Drawing Aids dialog box (DDRMODES command). To signal that the selection set is complete, and to move on with the rest of the editing command you are using, press the Enter key or the spacebar at the Select Objects: prompt.

The general selection process provides you with a variety of options with which to select the desired objects:

All of the preceding options are discussed in detail in the following sections.

Picking the Object

As you are prompted to directly select objects, the normal pointer is replaced with a box cursor, which is referred to as the pickbox. To select an object directly, position the pickbox over the object and select it. The size of the pickbox is controlled through the Object Selection Settings dialog box (see fig. 10.3).

Figure 10.3 The Object Selection Settings dialog box of DDSELECT enables you to control various aspects of the selection process.


Using Implied Windowing

When you position the pickbox over an empty portion of the drawing and pick a point, the system assumes that you want to anchor a rectangular window at that point. You determine its size by dragging its outline and then picking a second point (the opposing diagonal corner point relative to the anchor point). When the window is defined from left to right, then all objects completely enclosed in the window are selected. As shown in figure 10.4, using a window would result in just the circle being selected. When the window is defined right to left, it is referred to as a crossing window. In a crossing window, all objects that are completely enclosed in the window or that merely cross the boundaries of the window are selected. A crossing window is drawn with a dashed linetype, whereas a window is drawn with a continuous linetype. As shown in figure 10.4, using a crossing window would result in the circle and the three lines being selected. If you disable the Implied Windowing setting in the Object Selection Settings dialog box, then this facility is disabled.

Figure 10.4 Using a window versus a crossing window to select objects.


Using a Window

With the Window option, you are explicitly defining a window with which to select objects. With a window, you pick two points to define the size and location of a rectangular window. All objects completely enclosed in the window are selected. Unlike an implied window, the first point selected need not be located in an empty portion of the drawing. Furthermore, it does not matter whether the window is defined left to right or right to left. The Window option is superior over an implied window when you deal with a crowded drawing and encounter difficulties finding an empty area of the drawing in which to anchor the implied window.

Using a Crossing Window

The Crossing option is similar to the Window option, except that, in this case, all objects that are completely enclosed in the window or that cross the window's boundaries are selected.

Selecting the Last Object

The Last option automatically selects the last object drawn.

Selecting ALL Objects

The ALL option selects all objects not residing on a locked or frozen layer. This option will select objects even if they are not visible in the current view. Be careful in using this option with the ERASE command.

Using a Fence

This option enables you to define a series of temporary line segments, which is referred to as a fence. All objects that the fence intersects are selected. The fence segments themselves are drawn as dashed lines as shown in figure 10.5. In figure 10.5, only the lines and not the circle would be selected.

Figure 10.5 Using the Fence option to select the lines.

Using a Window Polygon

The Wpolygon (Window Polygon) option is similar to the Window option, except that, in this case, you define an irregular polygon-shaped window rather than a rectangular window. Figure 10.6 illustrates using the polygon option to select just the circle and bottom line. You may define the window polygon with as many points as necessary. The Wpolygon option automatically draws the closing segment back to the beginning point.

Figure 10.6 Using the Wpolygon option.

Using a Crossing Polygon

The Cpolygon option is similar to the Crossing option, except that, in this case, you define an irregular polygon-shaped window rather than a rectangular window. Figure 10.7 illustrates using the Cpolygon option to select the circle and two of the three lines.

Figure 10.7 Using the Cpolygon option.

Previous

This option enables you to select the selection set assembled in the previous command.

Picking Multiple Objects Directly

Generally, as you select each object directly, the point is processed and any object that is found in the area covered by the pickbox is highlighted and selected. Then another Select objects prompt is displayed. With the Multiple option invoked, however, the pick points are not processed and the selected objects are not highlighted until you press the Enter key or the spacebar.

Selecting Groups

The Group option enables you to specify the name of a defined group. Groups are discussed later in this chapter, in the section entitled "Creating and Editing Groups."

Undo Option

The Undo option undoes the last option performed. Rather than typing the letter U, you can invoke this option with the Undo tool, located on the Standard toolbar.

Removing Objects from the Selection Set

By default, you work in the Add mode, so that any objects selected automatically are added to the selection set. The Remove option switches you to the Remove mode. In this mode, all objects selected are removed from the selection set. Undo is often used to remove the objects just selected from the selection set, but the Remove option enables you to select only the specific objects you want to remove from the selection set. You remain in the Remove mode until you either end the selection process (by pressing the Enter key or the spacebar) or by invoking the Add option.

Adding Objects to the Selection Set

This option switches you from the Remove mode back to the Add mode. By default, the general selection process starts off in the Add mode.

Holding Down the Shift Key

Instead of using the Remove option switch into the Remove mode, you can hold down the Shift key as you select objects already in the selection set (already highlighted). This action also causes the objects to be removed from the selection set. You can hold down the Shift key in combination with any of the aforementioned methods of selecting objects. Once you let go of the Shift key, you immediately are placed back into the Add mode, and all subsequently selected objects are added to the selection set.

Using Object Cycling

In a crowded drawing, it is sometimes difficult to select an object directly without inadvertently picking another nearby object. In such situations, you can magnify the view of the area, making it easier to select the required object. You also can use object cycling to ease this process.

To use object cycling, position the pickbox over the desired object once you are at the Select Objects: prompt. While holding down the Ctrl key, pick that point. Holding down the Ctrl key initiates object cycling, so an object occupying the area of the pickbox is highlighted. The next time you left-click (without holding down the Ctrl key), another object occupying the area of the pickbox is highlighted. If the highlighted object is not the required object, however, simply left-click again and the next object residing in the area of the original pick location is highlighted. Every time you left-click, the next object found in the area of the original pick location is highlighted until you cycle back to the first highlighted object. When the desired object is highlighted, you can end the cycling by pressing the Enter key or the spacebar, or by right-clicking.

As you continue to left-click and highlight the various objects, the actual physical location of the pickbox is immaterial. The location of the pickbox at the time you initiate object cycling is what defines the area that is searched.

So far, this chapter has discussed how to select objects for editing. The next section discusses how to search for objects that have certain like attributes. This process is called object filtering.

In addition to the options listed earlier, you can use several other options, including BOX, AUto, and Single. These options are commonly used by programmers defining new AutoLISP and ARX-based commands or new menu macros.

The selection options previously discussed are only usable if you choose the command first and respond to the command's prompt to select objects.

TIP: Highlighting selected objects is enabled by the Highlight setting in the Drawing Aids dialog box, accessed via the Tools menu. Generally, highlighting is enabled, but it can be disabled inadvertently when you interrupt a macro or a program that manipulates the setting. If you see that objects are not being highlighted as you select them, check this setting.

The Object Selection Settings dialog box (refer to fig. 10.3) is displayed by choosing Selection from the Tools menu. In this dialog box, you can find the settings to control various aspects of the selection process. The following sections discuss these settings in more detail.

Dealing with Noun/Verb Selecting

The first option in the Object Selection Settings dialog box is Noun/Verb Selection, which is enabled by default. With this setting enabled, you have the option to select the objects to be manipulated prior to invoking the command you want to use. When the Noun/Verb option is disabled, you must invoke the command first and then select the objects to be modified. This option affects only commands that start with the Select Objects: prompt (such as the ERASE or LIST commands), which, as discussed in the previous section, signals the beginning of the general selection process.

TIP: Working with the enabled Noun/Verb option can be confusing. You might consider turning the option off until you are comfortable with the process of selecting objects and using the various editing commands themselves. If you leave Noun/Verb enabled and accidentally select objects before choosing a command, simply press the Esc key to deselect the objects. Press the Esc key once more to get rid of the blue grip boxes. (These boxes are discussed in more detail later in the chapter.)

If you choose to select objects and then select the command, you are limited to picking objects directly, or using an implied window, both of which are discussed in detail in the next section.

Replacing and Adding Additional Selected Objects with the Use Shift to Add Option

The Use Shift to Add setting in the Object Selection Settings dialog box is disabled by default. As such, when you select additional objects in the Add mode of the general selection process, the objects automatically are added to previously selected objects. If you enable the Use Shift to Add option, any selection of objects after the initial selection process replaces the previously selected objects rather than adding to them. To add more objects to those previously selected, you must hold down the Shift key as you select the additional objects.

TIP: This option is provided for compatibility with the way other Windows 95 applications deal with selecting objects. With AutoCAD, having to press the Shift key to select additional objects is just another unneeded step. As such, leave this option disabled.

The Press and Drag option is the next setting in the Object Selection Settings dialog box and is discussed in the next section.

Using Press and Drag

Generally, the Press and Drag option in the Object Selection Settings dialog box is disabled. Consequently, when you define a rectangular window--(whether it be an implied window, window, or crossing window)--you do so by picking an initial point to anchor one corner of the window. You then pick another point as the location of the opposing corner point. With Press and Drag enabled, you first pick the initial corner point and then must continue to depress the pick button as you drag the shape of the rectangular window on your screen. You define the location of the second corner point by releasing the pick button. Enabling this option makes the process of selecting objects with a rectangular window in AutoCAD compatible with the process of using a window to select objects in Windows NT or Windows 95 itself. Whether you enable this option or not is a matter of user preference.

Using Implied Windowing

By default, the Implied Windowing option in the Object Selection settings dialog box is enabled. If you disable this setting, the only way you can define a window or a crossing window in the general selection process is to choose to use the Window or Crossing window options. Implied Windowing is very useful and the option to disable it is provided simply for backward-compatibility with previous versions of AutoCAD. The Implied Windowing setting only affects the general object selection process. Even with this setting disabled, you will still be able to select objects with an implied window at the Command: prompt for use with the grip commands or with the Noun/Verb setting. Grips are discussed in detail in the section titled "Using Grip Editing Commands." This ends the discussion of the Object Selection Settings dialog box. In the next section, the usage of object filters is discussed.

Using Object Selection Filters

Object filtering enables you to search for objects based on certain attributes. For example, you could use object filtering to select all circles in a drawing with a specific radius. To invoke object filtering, type the command FILTER at the Select Objects: prompt. This displays the Object Selection Filters dialog box (see fig. 10.8).

Figure 10.8 The Object Selection Filters dialog box of FILTER initiates object filtering.

You can then assemble a list of the properties, also known as filters, with which you want to conduct the search. Then, by clicking on the Apply button, you can select a group of objects within which you want to find those objects that meet your list of characteristics. The following sections discuss how to define your list of filters.

Defining a Simple Selection Criteria for Filters

A filter can be a type of object or a characteristic of that type of object. For example, you can search for arcs in general or arcs that have a specific radius. The list of available filters is extensive and is displayed by choosing the Filters drop-down list. If you choose a characteristic of an object, you also must supply the specific value of that characteristic that you seek with the text-edit box, located below the filter list. For some properties, you can use the Select button to choose the specific value from a list of valid values. For other properties, you must type that value in the text-edit box.

After you select the property and its associated value (if any), click on the Add to List button to add the property to the list of filters. You then should select the objects you want to search by clicking on the Apply button.

To remove a filter from the list, choose the filter and press the Delete button. To edit the specific value of a filter on the list, select the filter and click on the Edit Item button. After changing the value of the property, click on the Substitute button to replace the old property with the revised property.

Defining a Complex Selection Criteria for Filters

The search criteria employed can be a complex set consisting of multiple filters. By default, when you assemble a list of filters, only objects that meet all the individual filters are selected. For example, you could choose to select only arcs that reside on the layer CURVES by choosing the Arc and Layer filters. In doing so, you assemble a list of properties that must be met; this is referred to as an AND conditional. When you assemble a list of properties, the system assumes that you are assembling an AND conditional. Other options do exist, however.

The most common option is to create an OR conditional. In an OR conditional, the objects must meet only one of the conditions, not all of them. For example, you could assemble a list of properties such that any object that is an arc or that resides on the CURVES layer is selected. You begin an OR conditional by choosing the **Begin OR filter. Then you assemble the various properties in which you are interested. You end the list of properties with the **End OR filter.

The list of filters can consist of AND and OR conditionals nested within each other, but for most users a simple search criteria consisting of a single filter is enough.

TIP: To gain an idea of the properties that are available for a particular object, click on the Add Selected Object button and choose a single object. All the relevant filters and their specific values for the selected object automatically are assembled into a list. You then can delete the filters you do not need, leaving only the properties for which you want to search.

Saving and Restoring the Criteria for Filters

To save a list of properties you have assembled so that the list can be reused at a later date or in another drawing, type a name in the Save As text-edit box and click on the Save As button. The next time you want to use that filter, simply select its name from the Current drop-down list. To delete a named filter list, select the name from the Current drop-down list and click on the Delete Current Filter List button. Named filter lists are saved in the file FILTER.NFL, which is created in the working directory when you initially click on the Save As button.

In addition to searching for objects that share certain properties, you can link disparate objects together in order to select them as a group. This process is discussed in the following section.

Creating and Editing Groups

You can link disparate objects on different layers into what is referred to as a group. Once a group is created, all the member objects of the group can be selected by selecting one member of the group or by naming the group. Assembling the objects into a group, however, does not prevent you from editing the member objects individually. To create and edit a group, you can use the GROUP command, which you initiate by choosing Object Group from the Tools menu (see fig. 10.9).

The following sections discuss how to use the GROUP command for specific tasks.

Figure 10.9 The Object Grouping dialog box of GROUP enables you to create and edit a group.

Creating a Group

Every group must have a name. To create a group, you first type a name in the Group Name text-edit box. Then, click on the New button and select the objects you want to include in the group. To complete the creation of the group within the drawing you must click on the OK button in the Object Grouping dialog box. If you do not want to name the group, enable the Unnamed option, and AutoCAD will give the group an arbitrary name that begins with an asterisk. Unnamed groups also are created when you duplicate a group using commands such as COPY or ARRAY. To include unnamed groups in the list of groups displayed in the dialog box, enable the Include Unnamed option.

By default, any group you create is selectable. This means that the group of objects can be selected by name or by selecting a member. If you turn off the Selectable option before you create a group, the group will not be selectable. The individual group members still will be listed as members of the group, but they will be selectable only as individual objects. One reason you might want to create a non-selectable group is that you want to associate various objects together for use with custom programs (created by you or a third-party developer) that interact with the drawing database but are not for use with AutoCAD editing commands. The use of non-selectable groups is generally not done by typical users; so as a rule, always make your groups selectable.

A group can have as many members as you desire, and an individual object can be a member of more than one group. The group description is an optional piece of information that you use to better describe the contents of the group or the relationship between the member objects.

Selecting a Group to Edit

After you create a selectable group, you can select all members of the group simply by selecting any one group member or by naming the group. Whether all members of a selectable group also are selected when one member is selected is controlled by the Object Grouping setting in the Object Selection Settings dialog box. The Object Grouping setting can be enabled or disabled with the Ctrl+A key sequence. Even with the Object Grouping setting disabled, the members of a selectable group always can be selected simply by naming the group at the Select Objects: prompt.

To select a group by name, specify the Group option at the Select Objects: prompt (type G at the prompt).

Inquiring About a Group's Membership

If you ever forget whether an object is a member of a group or which objects are members of a particular group, you can use several buttons to find this information. Use the Find Name button to determine the group, if any, to which a selected object belongs. Select a group name from the list of group names, and choose the Highlight button to show all the members of the selected group highlighted on-screen. You also can use the LIST command to see the groups, if any, to which selected objects belong.

Modifying an Existing Group

To modify the makeup of a particular group, first select the group name from the list of groups. The following list shows the buttons you use to modify the group you select (refer to fig. 10.9):

Deleting a Group

To remove or undefine a group, use the Explode button (not the EXPLODE command) of the Object Grouping dialog box (refer to fig. 10.9). Exploding a group dissolves the associations between the member objects but does not erase the member objects.

The previous sections have discussed the various ways to select an object or objects for editing. After you have selected the object, you can change its properties, as discussed in the following section.

Changing an Object's Properties

The properties of an object are defined as its layer, color, and linetype and, for most objects, also include its object linetype scale and/or thickness. You can use the Object Properties toolbar, the Properties tool off the Object Properties toolbar, or the Match Properties tool off the Standard toolbar to change an object's properties (see fig. 10.10).

Figure 10.10 The Standard and Object Properties toolbar.

Editing with the Object Properties Toolbar

The Object Properties toolbar is used to change the layer, color, and linetype of selected objects. At the Command: prompt, select the object or objects you want to change. The layer, color, and linetype drop-down lists display the current settings of the selected objects. If you have selected multiple objects for editing, and a particular property varies for the selected objects, the corresponding drop-down list displays a blank value. To change a specific property of the selected objects, choose the appropriate drop-down list and choose a new setting.

NOTE: To use the Object Properties toolbar to change the properties of selected objects, you must have the Noun/Verb setting in the Object Selection Settings dialog box enabled.

Using the Properties Tool

You can use the Properties tool from the Object Properties toolbar or the Modify menu to change the properties of selected objects. If you select a single object, the Modify dialog box is displayed (see fig. 10.11).

Figure 10.11 The Modify Line dialog box of DDMODIFY is displayed if a single line is selected.

If you select more than one object, the Change Properties dialog box is displayed (see fig. 10.12).

Figure 10.12 The Change Properties dialog box of DDCHROP is displayed if multiple objects are selected.

The appearance of the Modify dialog box is adjusted for the type of object displayed. The top portion of the dialog box contains the general properties of the object, while the bottom portion contains the properties specific to that type of object. The lower portion changes depending on the type of object selected.

The Change Properties dialog box is, in effect, just the top portion of the Modify dialog box.

Using the Match Properties Tool

The Match Properties command can be chosen from the Standard toolbar or the Modify menu. The Match Properties command enables you to change specific properties of selected objects to match the corresponding properties of a source object. The following steps are necessary to use this command:

1. Choose the source property, the object you want to emulate.

2. Using the Settings option, choose the properties of the destination objects to be changed. The default changes all properties.

3. Select the destination objects, the properties of which are changed to match the properties of the source object.

In the next exercise, you will create a group and change the layer property of one of the computers in the drawing.

CREATING GROUPS AND MODIFYING THE PROPERTIES OF OBJECTS

1. Continue to use the drawing MODIFY.DWG. Choose Named Views from the View pull-down menu, select the view named OFFICE-A. Click on the Restore button on the View Control dialog and then click on the OK button to restore the view OFFICE-A.

2. Select the computer on the desk by picking 1 (see fig. 10.13) at the Command: prompt. The computer is drawn with a block, which is discussed in Chapter 12, "Creating and Using Blocks."

3. Note that the layer displayed in the Layer drop-down list is the CPU-486 layer on which the computer is inserted. Choose the Layer drop-down list and select the layer CPU-PENTIUM. You have just moved the computer to a different layer.

4. Press the Esc key twice. This de-selects the computer and shuts off the display of the grip points.

Figure 10.13 Modifying the layer of the computer in Office-A.

5. Restore the view OFFICE-D. Choose Named Views from the View pull-down menu, select the view named OFFICE-D. Click on the Restore button on the View Control dialog box and then the OK button to restore the view. Choose Object Group from the Tools menu. Enter PENTIUM COMPUTERS into the Group Name text-edit box and click on the New button. Pick 1 and 2 (see fig. 10.14) to select those two computers to include in the new group. Press the Enter key to exit object selection--the Object Grouping dialog box is re-displayed. Click on the OK button.

Figure 10.14 Creating a group consisting of two computers.

6. Choose Selection from the Tools pull-down menu. Make sure that the Object Grouping setting is enabled in the Object Selection Settings dialog box. Click on the OK button.

7. Pick 1 again. Notice that both computers were selected. Choose the Layer drop-down list and select the CPU-PENTIUM layer. Press Esc twice.

8. Save the drawing.

Sometimes you might want to modify existing objects, as discussed in the previous sections. At other times, you might want to remove selected objects from a drawing entirely. The following section explains how to do so.

Erasing 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. The command starts with the Select Objects: prompt, signaling the start of the general selection process. 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 then are erased. If Noun/Verb is enabled, you can select the objects first and then choose the ERASE command.

If you erase any objects by accident, you can undo the ERASE command. A specific command also can be used to retrieve erased objects. Type the OOPS command whenever you want to retrieve the objects removed with the last ERASE command without affecting any other editing performed since the last ERASE command.

In addition to erasing objects, we have a group of editing commands referred to as grip editing commands. These grip commands are the topic of the next section.

Using Grip Editing Commands

Grip editing is a facility that integrates object snap points with the most commonly used editing commands and then places the combined capabilities literally at your fingertips. With grips, it is possible to edit objects and select specific object snap points without ever having to pick a tool, use a menu command, or type a command. In the following sections, you will learn how to enable grip modes, activate grips, and make use of the various options available with grips.

Enabling Grip Modes

Grip modes are an optional facility that you can choose to use. By default, grips are enabled, but if you want, you can disable grips by disabling the Enable Grips setting in the Grips dialog box (see fig. 10.15), which is displayed by choosing Grips from the Tools menu.

Figure 10.15 The Grips dialog box of DDGRIPS controls how grips behave.

With grips enabled, you start the process of using grip modes by selecting the objects you want to edit at the Command: prompt. In other words, you do not initiate any commands. Instead, you simply select the objects by picking them or by using implied windowing. After you have selected the objects, the objects' grip points are displayed as blue squares. The color and size of these "unselected grip points" are set with the Unselected button in the Grips dialog box. The displayed grip points correspond to the control points of the objects, and for the most part, these points are the same as the object snap points for the various types of objects. The major exceptions to this rule are discussed in table 10.1.

Table 10.1 Specific Grip and Object Snap Discrepancies

Object Description
Arc Only three grip points exist for an arc: its endpoints and its midpoint. In contrast, object snap points include the center point and visible quadrant points.
Block Insertion By default, only one grip point is displayed at the insertion point of each block insertion. However, if you enable the Enable Grips Within Blocks setting of the Grips dialog box, then the grip points of all the component objects are also displayed.
Elliptical arc Grip points correspond to the arc's endpoints, midpoint, and center points but not to its visible quadrant points.
Mline Grip points exist at the points used to locate the mline object. In contrast, endpoint and midpoint object snap points exist on each visible segment.
Mtext Four grip points exist per mtext object, one at each corner of the imaginary box that surrounds each mtext object. In contrast, only one insertion object snap point exists per mtext object.
Spline A grip point exists at every point used to define the spline, known as the spline's control points. Object snap points include only the endpoints.

As with object snap, grip points enable you to easily choose a very specific point on an object. After the grip points are displayed, you must choose one point to activate grip modes.

Activating Grip Modes

After you have selected the objects to be edited, and after the grip points are displayed, you initiate the grip mode commands by picking one of the grip points. The grip points affect the cursor much like object snap points do--the grip points act as magnets and pull the cursor into the box.

After a grip point is selected, it is displayed as a red box and is referred to as a selected grip point. The color used to fill in the grip box is set with the Selected button in the Grips dialog box. The selected grip point subsequently is used as the base point for the various grip mode commands: stretch, move, rotate, scale, and mirror. Initially, the Stretch grip command is activated, but you can press the spacebar to cycle through the other grip commands. Alternatively, right-click and pick the desired grip command from the menu that appears. The various mode options are discussed in the following sections.

Deactivating Grip Points and Commands

When you select objects at the Command: prompt, the grip points of the objects are displayed and the objects are highlighted. The highlighting indicates the objects have been selected. If you press the Esc key once, the objects will be de-selected (no longer highlighted) but the grip points will still be displayed. To erase the display of the grip points, you need to press the Esc key one more time. In previous versions of AutoCAD, a common procedure that was employed was to select objects and press the Esc key once so that the objects' grip points could be selected (much like snap points) during a grip command but not affect the objects themselves. You could also selectively de-select highlighted objects by pressing the Shift key and selecting the highlighted objects thereby leaving the grip points displayed. These two procedures still work in R14, but the new Autosnap feature makes them irrelevant because Autosnap automatically displays the snap points on nearby objects.

Another common problem that users run into using grips is that they accidentally select objects and activate the grip command mode by selecting one of the grip points. To exit grip command mode, just press the Esc key. Remember, in AutoCAD, pressing the Esc key always cancels the current operation. To de-select the objects and erase the display of the grip points, press the Esc key two more times.

Using the Stretch Mode

The default grip command is Stretch, which enables you to relocate the selected grip point. This in turn affects only the object or objects that are defined by the selected grip point. For example, if the selected grip point is the endpoint of a line (as shown in figure 10.16), then that endpoint of the line is moved to the new position.

Figure 10.16 Using Grips to stretch two lines.

If the selected grip point is the endpoint at which two lines meet, then both lines are stretched to the new endpoint location. As you decide on the new location of the selected grip point, notice that the rubber band is anchored at the selected grip point. Thus, the selected grip point is referred to as the base point of the stretch.

Stretching Multiple Points at the Same Time

If you want to stretch more than one point at a time, you must initiate a modified procedure to activate grips. First, you must select all the grip points that you want to move during the stretching procedure while holding down the Shift key. Then, after releasing Shift, pick the grip point that you want to use as the base point of the stretching. This last pick activates the grip commands.

Using Relative Coordinates

If you know the exact delta-X, delta-Y, delta-Z, or distance and angle you want to apply to the selected grip point, you can use relative coordinates rather than picking the new location. You also can define the distance and direction of the stretch with direct distance entry.

The next grip command to be discussed is the Move mode.

Using the Move Mode

Use the Move grip command simply to move the selected objects to the new location. Unlike the Stretch grip command--in which only the selected objects that are controlled by the selected grip point are affected--all selected objects are moved with the Move command (see fig. 10.17).

Figure 10.17 The Move grip command moves all selected objects.

As with the Stretch grip command, the selected grip point is used as the base point for the move. If you know the exact delta-X, delta-Y, delta-Z, or distance and angle you want to apply to the selected grip point, you can use relative coordinates rather than picking the new location. You also can define the distance and direction of the move with direct distance entry.

Using the Rotate Mode

The Rotate grip command enables you to rotate the selected objects about the selected grip point (see fig. 10.18).

Figure 10.18 Grips can be used to rotate selected objects.

You can specify the amount of rotation to apply to the selected objects graphically by using the rubber band or by typing the specific value. Alternatively, you can specify the Reference option.

To use the Reference option, you first must define a reference angle--either a real or imaginary line--by picking its two endpoints or typing an angular value. Then, you must specify the angle to which you want the reference line to be rotated by dragging or typing the angle.

TIP: The Reference option is useful when you know the angle to which you want to rotate a known reference line but do not know the exact amount of rotation needed.

Using the Scale Mode

The Scale grip command enables you to scale the selected objects about the selected grip point. You can either type the scale factor or pick a point. Picking a point defines the length of the rubber band, which is subsequently used as the scale factor. The grip point is the static point about which the objects expand or contract. Just as with the Rotate grip command, the Scale grip command has a Reference option.

To use the Reference option, you first must define a reference length--either a real or imaginary line--by picking its endpoints or typing a known length value. Then, you must specify the length to which you want the reference line to be scaled. The second length can be defined by typing the new length or picking a point, in which case the length is the length of the rubber band.

Using the Mirror Mode

The Mirror grip command enables you to mirror the selected objects about the mirror line that is anchored at the selected grip point (see fig. 10.19).

Figure 10.19 The Mirror grip command enables you to mirror objects.

The mirror line is the line about which all the selected objects are flipped. Text and mtext objects also are flipped so that they appear backward. If you want the text and mtext objects to remain readable, type MIRRTEXT at the Command: prompt, and set the system variable to 0.

Invoking the Base Point Option

The Base point option enables you to relocate the anchor point of the rubber band. For the Stretch grip command, relocating the base point does not affect the grip point that is stretched. A Base point option exists in each grip mode command prompt.

Invoking the Copy Option

A Copy option also exists in each grip mode command prompt. When this option is invoked, the original objects are left untouched and the changes are made to copies of the originals. Invoking the Copy option also enables you to make multiple copies for each of the grip commands.

An alternative to specifying the Copy option is to hold down the Shift key as you pick the point to complete the command. Be aware, however, that if you continue to press the Shift key, the system uses the distance and direction from the original object to the first copy point to overlay a set of invisible snap points. (This process works in a manner similar to the SNAP command.) For the Stretch, Move, and Scale commands, the snap points are arranged into a grid, with one of the grid axes running from the base point to the first selected point (see fig. 10.20).

Figure 10.20 The Shift key can be used to place copies with temporary invisible snap points that are arranged into a grid.

For the Rotate and Mirror grip commands, the snap points are arranged into a circular arrangement such that the angular displacement between adjacent snap points is equal (see fig. 10.21).

Figure 10.21 The Shift key also can be used to place copies with temporary snap points that are arranged into a polar configuration.

In the next exercise, you will use grips to make changes and additions to the office layout in the drawing MODIFY. These changes include rotating and duplicating a chair in the office layout and stretching the cabinet.

USING GRIPS TO MAKE CHANGES AND ADDITIONS

1. Continue to use the drawing MODIFY.DWG. Choose Named Views from the View pull-down menu, select the view named OFFICE-A. Click on the Restore button on the View Control dialog box and then the OK button to restore the view OFFICE-A. At the Command: prompt, pick the chair located below the desk and the other chair (see fig. 10.22). This chair is a block insertion, which explains why only one grip point is displayed.

Figure 10.22 Grips can be used to stretch the cabinet and rotate and duplicate a chair in this drawing.

2. Select the grip point. You have just activated the grip commands and the default command, Stretch. Right-click and a menu should appear on the screen. Choose Rotate from the menu, and type 180. You have just rotated the chair 180 degrees.

3. Select the same grip point, and press the spacebar once. You have just cycled to the Move grip command. Now type C to specify the Copy option. Now type @3'<270. You have just made a duplicate, which is located 3' below the original chair. Press the Enter key to exit the Move grip command, and press Esc twice.

4. At the Command: prompt, use Implied Windowing to pick 1 and 2 to select the cabinet. Because the cabinet was drawn with four lines, it has grip points at the endpoints and midpoints.

5. While holding down the Shift key, pick 3 and 4. Holding down the Shift key enables you to select multiple points to stretch. Release Shift, and pick 1 to activate the grip commands and the default grip command, Stretch. Type @2'<0 to stretch the rectangle 2' to the right, and press Esc twice.

6. Refer to step 1 and restore the view OFFICE-B. At the Command: prompt, select the chair (see fig. 10.23), and pick the grip point to enable the grip commands. Right-click and choose Rotate, and then right-click and choose Basepoint. Holding the Shift key, right-click the mouse and select CENter from the Object Snap pop-up menu, pick 1. Right-click and choose Copy. Then type 90, 180, and 270 to make three copies. Press the Enter key once to exit the Rotate grip command. Press the Esc key twice.

Figure 10.23 The Rotate and Copy commands enable you to make duplicates in a polar (or circular) arrangement.

7. Refer to step 1 and restore the view OFFICE-E. At the Command: prompt, select the office cubicles on the left side of the room with an implied crossing window by picking 1 and 2 (see fig. 10.24). Pick one of the displayed grip points. Right-click and pick Mirror, and then right-click and pick Copy. Now right-click and choose Base Point. Then, using Midpoint object snap, pick 3. Enable Ortho mode and pick 4. By enabling Ortho mode, you ensure that you create a horizontal or vertical mirror line. Press the Enter key to exit Mirror grip command. Press the Esc key twice.

8. Save your drawing.

Figure 10.24 The Mirror and Copy commands enable you to create a mirrored copy.

Undoing Changes

In previous sections, you learned to use the Undo tool on the Standard toolbar to undo the effects of the last command or to specify the Undo option of a specific command (such as the LINE command). The Undo tool subsequently issued the U command or option. A more powerful version of the U command also exists: the UNDO command, issued by typing UNDO: at the Command: prompt. The various options of the UNDO command are discussed in the following sections.

Undoing Multiple Commands

The U command is used to undo the effects of a command one command at a time. With UNDO, you can specify the number of commands to be undone by typing the number of commands you want to undo at the UNDO: command prompt. The REDO command undoes the effects of the UNDO command regardless of the number of options that you specify within a single UNDO. Often, however, you will not know exactly how many commands you must undo to revert the drawing to a previous state. In these cases, markers prove handy.

Leaving and Using Markers

When you specify the Mark option of the UNDO command, a mark (a device much like a bookmark) is placed in the Undo information file that is maintained by AutoCAD. Later, during the drawing session, specifying the Back option instructs the UNDO command to undo all the commands issued since the last time the Mark option was specified. In addition to undoing the commands, the Back option also removes the last mark. You can issue the Mark option of the UNDO command as many times as you want during a drawing session.

TIP: Issue the Mark option when you think that you will make changes to the drawing that you are not certain you will want to keep. Then, if you decide to discard the changes, simply issue the Back option. Alternatively, you can save the drawing before you make the changes, and if you want to discard the changes, you can issue the OPEN command, discard the changes, and open the same drawing once again.

UNDO also enables you to control the scope of the UNDO facility and is discussed in the next section.

Controlling UNDO

The Control option enables you to specify how powerful the UNDO and U commands are. By default, AutoCAD keeps track of all the commands issued in a drawing session, which enables you to undo any number of commands you want. You can, however, choose to disable the ability to undo commands by choosing the None option. You also 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--this is because keeping track of commands issued takes up drive space. In such situations, it is better to allocate more free drive space than to limit the ability of AutoCAD to undo commands.

Resizing Objects

In addition to the grip editing commands, a number of other commands can be used to modify existing objects. Two of these grip editing commands--Stretch and Scale--are used to resize objects. Other commands that can be used to resize objects are SCALE, STRETCH, LENGTHEN, TRIM, EXTEND, and BREAK, all of which are covered in this section. These commands can be found on both the Modify toolbar and menu.

Scaling Objects

As with the Scale grip command, the SCALE command is used to scale objects up or down in size. The major difference between the two scaling commands is that with grips, the options that you have for selecting objects are limited to picking the objects directly and using an implied window. The SCALE command employs the general selection process, which gives you more options for selecting the objects. After selecting the objects to be scaled, you are prompted to select a base point that is the equivalent to the grip point that you select when you edit objects with the grip commands. You then can enter a scaling factor by typing or picking a point, or you can specify the Reference option. If you pick a point, the length of the rubber band is used as the scaling factor.

TIP: One advantage that the Scale grip command has over the SCALE command is that this command enables you to use the Copy option to scale and make copies of the selected objects simultaneously.

The next section discusses the STRETCH command.

Stretching Objects

As with the Stretch grip command, the STRETCH command is used to stretch an object's length by moving a portion of the object. Although the command does issue the general Select Objects: prompt, you must select the desired objects in a specific manner by using an implied crossing window, the Crossing window, or Cpolygon options. This is because the objects to be stretched must be selected with a crossing window of some sort. You can use only one crossing window per occurrence of the STRETCH command. If you define more than one crossing window in selecting the objects, only the objects selected with the last crossing window are stretched.

After completing the selection of the objects, you are prompted to select a base point or enter a displacement. The base point is the equivalent of the selected grip point in grip editing. If you choose to pick a base point, you also must specify a second point for the new location of the base point. As an alternative to picking a base point, you can specify a displacement.

The displacement is defined as the delta-X, delta-Y, and delta-Z--or the distance and angle from the base point to the second point, which is essentially the amount of stretching you want to apply to the objects. If you know the exact displacement desired, you can enter the displacement at the prompt for the base point. The displacement is entered as an absolute Cartesian coordinate or polar coordinate. Initially, the STRETCH command interprets the displacement as a point and anchors the rubber band at that point. You force the STRETCH command to interpret the numbers as a displacement by pressing the Enter key or the spacebar at the prompt for the second point. (In other words, do not define a second point.)

The STRETCH command moves all objects that are completely enclosed in the crossing window. Any objects not completely enclosed are stretched by moving the endpoints in the crossing window while keeping the endpoints outside the crossing window immobile.

TIP: The Stretch grip command offers two advantages over the STRETCH command. The Copy option of the Stretch grip command enables you to scale and make copies of the selected objects simultaneously. In addition, STRETCH cannot be used to stretch circles or ellipses, and the Stretch grip command can.

The next section deals with the LENGTHEN command, for which there is no equivalent grip command.

Lengthening and Shortening Objects

Any open object, such as a line or an arc, can be lengthened or shortened with the LENGTHEN command. Table 10.2 details the options at the initial prompt.

Table 10.2 The LENGTHEN Options

Option Description
Select object The default option involves selecting an object. When an object is selected, its length is displayed and the initial prompt is re-displayed.
DElta Use this option to specify the length by which the object is to be lengthened or shortened. Enter a positive value to lengthen the object, and enter a negative value to shorten the object. If the object to be affected is an arc, you have the option of entering a change in the arc length (the default) or a change in the included angle.
Percent Use this option to define the change as a percentage, where 100 percent is the original length. Enter a percentage greater than 100 percent to lengthen the object and a percentage less than 100 percent to shorten the object.
Total Use this option when you know the final length you want to the object to have.
Dynamic Use this option to drag the endpoint to the desired location. In dragging the endpoint of the object, the alignment of the object does not change.

After defining the amount of change to be applied, pick the object to be affected. The endpoint nearest the point used to select the object is the endpoint that is moved, so favor the endpoint that you want to affect in selecting the object. Although the prompt indicates that you can select only one object to lengthen at a time, you can select multiple objects with the Fence selection option. Simply type F at the <Select Object To Change>/Undo: prompt, and define the fence.

In addition to LENGTHEN, another command you can use to shorten objects is TRIM. TRIM is the topic of the next section.

Trimming Objects

Use the TRIM command to trim an object to an existing boundary. You begin the trimming process by selecting the object that defines the boundary, the cutting edge. You can select multiple cutting edges. You then select the object to be trimmed to the selected cutting edge. If you want to select more than one object at a time, use the Fence option to select multiple cutting edges or multiple objects to be trimmed.

Any edge object, such as a line or a circle, can be used as a cutting edge or can be the object being trimmed. An mline object, however, can be selected as a cutting edge, but cannot be trimmed.

With the TRIM command, the result is dependent on the point you use to select the object being trimmed (see fig. 10.25).

Figure 10.25 The result of TRIM varies with the point you pick.

Starting from the point that is used to select the object, the TRIM command proceeds in one direction along the object until it encounters either an endpoint or a cutting edge. Then the TRIM command proceeds from the original pick point in the opposite direction until it encounters either an endpoint or another cutting edge. The resulting portion of the object is then removed. Under no circumstances can an object be trimmed in such a way that nothing is left of the object.

Using the Edge Option to Extend the Cutting Edges

By default, the object to be trimmed must actually intersect with the cutting-edge object to which it is being trimmed. If you want, you can bypass this requirement with the Edge option. Choosing the Extend setting of the Edge option extends the cutting edges, if necessary, so the object being trimmed no longer must intersect the cutting edge.

Using the Project Option to Trim Objects in 3D Work

The Project option is used exclusively for 3D work in which the object being trimmed lies at a different elevation (Z coordinate) than the cutting edge. In such cases, the two objects can never actually intersect, but they can appear to intersect in a particular view. Using the Project option, you can instruct the TRIM command to initiate one of three actions:

TIP: If you press the Enter key without selecting any cutting edges, then all edge objects on the screen are automatically selected as valid cutting edges. In addition, an object that is selected as a cutting edge can itself be trimmed with the same TRIM command.

Not only can you trim objects but you can also extend objects and that is the topic of the next section.

Extending Objects

The EXTEND command is used to elongate an edge object to an existing boundary (see fig. 10.26).

Figure 10.26 You can extend a line by using the EXTEND command.

EXTEND is the complement to the TRIM command, so it has the same options. Instead of prompting you to select cutting edges, however, the EXTEND command prompts you to select boundary edges. The Project and Edge options are settings shared by the TRIM and EXTEND commands. This means that whenever you change the Edge and Project settings in the TRIM command, the EXTEND command also is affected.

Another command that can be used to trim an object is the BREAK command, which is discussed in the next section.

Breaking Objects

To remove a portion of an object, you can use the TRIM command or another command, the BREAK command. BREAK offers two advantages over TRIM for removing a portion of an object. First, you do not need any cutting objects to use BREAK. Second, the BREAK command can be used to break an object into two objects without removing any part of the two resulting objects.

After you select the object to be broken, the default option selects a second point on the object. Then the portion of the object between the point used to select the object and the second point is removed. In the case of curved edge objects, such as a circle, the removal process proceeds from the first point to the second point in a counter-clockwise direction. Sometimes, however, the point used to select the object is not where you want to begin the break. In this instance, you can use the First option to redefine the beginning point of the break and then choose the endpoint of the break.

If the second point (or the two points you pick for the First option) that you selected for the end of the break does not actually lie on the object to be broken, the point is projected back to the object and the projected point is used as the end of the break (see fig. 10.27).

If you simply want to break an object into two objects without actually removing a portion of the object, define the second point at the same location as the first point of the break. The easiest way to do this is to enter the relative coordinates @0,0 (or @ for short) as the second point.

Figure 10.27 The first option of the BREAK command enables you to determine the starting point of the break.

Relocating Objects Using MOVE, ROTATE, and ALIGN

In addition to the Move and Rotate grip commands, the MOVE, ROTATE, and ALIGN commands can be used to relocate and/or re-orient selected objects. MOVE and ROTATE are found on both the Modify menu and the toolbar. The ALIGN command is only found on the 3D Operations submenu under the Modify pull-down menu.

Moving Objects

As with the Move grip command, you use the MOVE command to move selected objects to a new location. After selecting the objects, select the base point for the move. The base point typically is chosen as a point on one of the objects being moved. You then pick a second point, which is the new location of the base point.

In reality, the MOVE command simply calculates the distance and direction from the first point to the second point and then uses that information for the move. Picking the base point such that it is on one of the objects being moved simply makes it easier for you to visualize the end result of the MOVE command. As an alternative to picking a base point, you can specify a displacement.

Specifying Displacement

The displacement is defined as the delta-X, delta-Y, and delta-Z--or the distance and angle from the base point to the second point. Essentially, this is the amount of movement you want to apply to the objects. If you know the exact displacement desired, you can enter the displacement at the prompt for the base point. The displacement is entered as an absolute Cartesian coordinate or polar coordinate. Initially, the MOVE command interprets the displacement as a point and anchors the rubber band at that point. You force the MOVE command to interpret the numbers as a displacement by pressing the Enter key or the spacebar at the prompt for the second point. (In other words, do not define a second point.)

TIP: The advantage of using MOVE over the Move grip command is the extra flexibility you gain with the general selection process employed by MOVE.

Rotating Objects

You can use the ROTATE command to rotate selected objects about a particular point, the base point of the rotation. After you pick the base point, the default option enables you to specify a rotation angle by typing the rotation angle, picking a point, or specifying the reference option. If you pick a point, the angle of the rubber band is used as the rotation angle.

TIP: One advantage of using the Rotate grip command is that with the Copy option, you can make copies and rotate the copies simultaneously. Another advantage of the Rotate grip command is that by pressing the Shift key, you can make evenly spaced copies arranged in a polar configuration. On the other hand, the ROTATE command gives you added flexibility in selecting the objects to be moved by employing the general selection process.

Aligning Objects

The ALIGN command initially was conceived as a 3D editing command, which explains why it is found in the 3D Operation submenu of the Modify menu. In 2D work, however, ALIGN can be very useful. In effect, it is a combination of the MOVE, ROTATE, and SCALE commands. ALIGN typically is used to align one object with another object (see fig. 10.28).

Figure 10.28 Using ALIGN enables you to move and rotate selected objects.

After selecting the objects to be aligned, you are prompted to specify up to three pairs of points. Each pair consists of a source point and a destination point. The source point is a point on the object to be aligned, and the destination point is the corresponding point on the object to which you want to align.

As you can see in figure 10.28, you must specify only two pairs of points in 2D work--simply press the Enter key when prompted for the third pair. The selected objects are moved from the first source point to the first destination point. Then the objects are rotated such that the edge defined by the first and second source points are aligned with the edge defined by the first and second destination points.

Finally, you have the option to scale the objects such that the length defined by the first and second source points is adjusted to be equal to the length defined by the first and second destination points. In effect, this scaling option serves the same function as the Reference option of the SCALE command.

Duplicating Objects

With the grip editing commands, you can use the Copy option to make copies of the selected objects. Depending on the specific grip command you use, you can create exact duplicates or mirrored, rotated, scaled, or stretched duplicates. You also can use the COPY, OFFSET, MIRROR, and ARRAY commands--and even the Clipboard--to make copies of selected objects.

Copying Objects

The COPY command is used to make exact duplicates of selected objects. After you select the objects to be duplicated, you are prompted to specify the base point of the displacement and a second point. The distance and direction from the first point to the second point is calculated and used to locate the duplicate objects. To aid you in visualizing the results, pick a base point on one of the objects to be duplicated (for example, the center of a circle). The second point then becomes the point on the duplicates that corresponds to the first point on the originals.

Defining a Displacement

The displacement is defined as the delta-X, delta-Y, and delta-Z--or the distance and angle from the base point to the second point. If you know the exact displacement, you can enter the displacement at the prompt for the base point. The displacement is entered in an absolute Cartesian coordinate or polar coordinate form. Initially, the COPY command interprets the displacement as a point and anchors the rubber band at that point. You force the COPY command to interpret the numbers as a displacement by pressing the Enter key or the spacebar at the prompt for the second point. (In other words, do not define a second point.)

Making Multiple Copies

Generally, COPY makes a single set of the duplicates of the selected objects. You can, however, use the Multiple option to make multiple duplicates of the selected objects. After you specify the Multiple option and choose an initial base point, the COPY command repeatedly prompts you to select a second displacement point to locate the duplicates. The Multiple COPY command is ended by pressing the Enter key.

Copying with Offsets

With the OFFSET command, you can create a copy offset a certain distance from the original object. At the initial prompt, you have the choice of entering the offset distance or using the Through option. To enter a specific offset distance, simply type the distance (or pick two points on the screen) at the initial prompt. Thereafter, you can select one object at a time to create an offset from the duplicate and choose the side of the original on which you want the duplicate made.

If you choose the Through option, then you must pick a point after you select the object you want to copy. The distance along a perpendicular from the point that you pick to the original object serves as the offset distance. The pick point also is used to control the side of the original on which the duplicate is made.

The copy made by the OFFSET command might or might not be an exact duplicate of the original. Table 10.3 lists the various types of objects you can choose with the OFFSET command and the shape of the resulting copy.

Table 10.3 Objects and Resulting Duplicate with OFFSET

Original Object Resulting Duplicate
arc The new arc is created so that it has the same included angle and center point as the original arc, but the arc length will change.
circle, ellipse The new circle or ellipse is created so that it has the same center point as the original circle or ellipse. The radius of the new circle on the axis lengths of the new ellipse will be different from the original object's radius on axis lengths.
line, ray, xline The new line, ray, or xline is an exact duplicate of the original.
lwpolyline The lengths of the line and arc segments of the new lwpolyline are adjusted such that the endpoints of the new polyline are located along a direction perpendicular to the corresponding endpoints on the original open lwpolyline. For an intermediate vertex point, the new vertex points are located along a direction that bisects the angle between the segments on either side of the vertex point.
spline The length and shape of the new spline are adjusted so that the endpoints of the new spline are located along a direction perpendicular to the corresponding endpoints on the original open spline.

Figure 10.29 Making copies of a circle, an arc, and an ellipse with OFFSET.

Creating a Mirror Image

With the MIRROR command, you can create a mirror image copy of the selected objects. After you select the objects to be mirrored, you are prompted to pick two points to define the location of the mirror line. The mirror line is the line, or axis, about which the mirror image is created. The mirror line itself does not have to be a real line.

The only option you have with the MIRROR command is whether or not the original objects should be deleted. The default is to not delete the original objects.

As with the MIRROR grip command, the copy of text and mtext objects will appear backward, like if you held a page of text up to a mirror. To prevent text from being flipped in the copy, set the system variable MIRRTEXT to 0 at the Command: prompt.

Creating Arrays of Objects

The ARRAY command is used to make multiple copies of selected objects such that the copies are arranged in rows and columns (a rectangular array) or in a circular arrangement (a polar array).

Creating a Rectangular Array

If you choose to create a rectangular array (see fig. 10.30), you are prompted to supply the number of rows and columns, the distance separating adjacent rows, and the distance separating adjacent columns.

Figure 10.30 Creating a rectangular array consisting of rows and four columns of copies.

Generally, you type the row and column distances. You can, however, specify the distances with a window (referred to as a unit cell) by picking the two corner points of the window at the Unit cell or distance between rows (---): prompt. The height of the window is used as the distance between rows, and the width of the window is used as the distance between columns.

If you type a negative distance for the distance between the columns, the columns are propagated in the negative direction along the X axis; otherwise, they are created in the positive X direction. If you type a negative distance for the distance between the rows, the rows are propagated in the negative direction along the Y axis; otherwise, they are created in the positive Y direction. If you choose to use a unit cell to specify the distances, then the direction in which the rows and columns are propagated is determined by the direction from the first window point to the second window point.

Creating a Polar Array

If you choose to create a polar array, you are prompted to specify the center point about which the copies are made, the number of items (or copies) you want to create (include the original as one item), and the angle to fill (see fig. 10.31).

The angle to fill is the angle that you want to occupy with your copies. The angle fill is used to determine the angular separation between adjacent items. For example, if you specify 6 items and 180 degrees as the fill angle, then the angular separation between adjacent items is 180 divided by 6, or 30 degrees. If a positive fill angle is specified, then the copies are made in a counterclockwise direction; otherwise, the copies are made in a clockwise direction.

Figure 10.31 Creating a polar array of copies creates a circular arrangement.

If you fail to supply the number of items (if you press Enter without typing the number of items) or the angle to fill (if you type 0 as the angle), then you are prompted to define the angle to be used as the angular separation between adjacent items in the array.

The final prompt gives you the choice of rotating or not rotating the copies. If you answer "Y," the default setting, then the copies are rotated about the single reference point of the selected objects as the copies are made. If you answer "N," then the copies are not rotated about the reference point of the selection set. The reference point of the selection set is determined from the last object selected. If a window of some type is used to select the objects, then the last object in the selection set is picked arbitrarily. The reference point selected is based on the type of object (see table 10.4).

Table 10.4

Point on Object Used as the Reference Point for a Polar Array

Object Reference Point Used
block insertion, text, mtext Insertion point
dimension objects One of the definition points of the dimension object
lines, rays, traces, mlines One of the endpoints
arcs, circles, ellipses The center point
lwpolylines, splines The first vertex point
xlines The point connecting an imaginary line perpendicular to the xline to the center point of the polar array

TIP: As long as you use the default setting of rotating the copies, the resulting polar array will appear to be symmetrical regardless of the objects selected.

Copying with the Clipboard

To copy using the clipboard, choose Copy from the Edit pull-down menu. This copies selected objects to the clipboard. Choose Copylink to copy the current view to the clipboard. Copylink copies all objects in the drawing but also preserves the current view of the drawing. As an alternative, you can use the Cut command to copy objects to the clipboard and remove them from the drawing.

If you choose Paste from the Edit menu in an AutoCAD drawing, the contents of the clipboard are inserted as a block with an arbitrary name. You will want to explode the insertion so that you do not have to deal with the arbitrary block name assigned by the Paste command. You cannot use Paste Special when the contents you want to paste are taken from another AutoCAD drawing.

You also can paste an entire drawing into the current drawing by dragging the icon of the file to be pasted into the current drawing.

See Chapter 25, "ActiveX Automation," for a more detailed discussion on how to use the clipboard to cut/copy and paste between AutoCAD and other applications. In the next exercise, you will create some duplicates using the ARRAY command.

CREATING A RECTANGULAR ARRAY OF DUPLICATES

1. Continue to use the drawing MODIFY.DWG. Choose Named Views from the View pull-down menu, select the view named OFFICE-C. Click on the Restore button on the View Control dialog box and then the OK button. Choose Array from the Modify tool-bar or the menu. Select the desk and chair, and choose the R (rectangular) option.

2. Type 3 for the number of columns and 4 for the number of rows (see fig. 10.32).

3. Type 10' for the distance between rows and -12' for the distance between columns.

NOTE: We are now finished with this drawing, so you may exit the drawing.

Figure 10.32 Creating a three row by four column array of copies with ARRAY.

Summary

In this chapter, you learned the general commands and tools used to select objects and then edit them. Grip commands give you access to the most common editing operations simply by selecting the objects to be edited and then activating one of the grip points. If you want more flexibility in selecting objects, you can use the command-line version of the various grip commands. For example, you can use the command-line command STRETCH or the grip command Stretch. In addition to the editing operations you can carry out with grips, there are quite a number of other editing commands, such as TRIM or EXTEND, that are available. The next chapter covers the other remaining editing commands not covered in this chapter and some additional bonus editing tools supplied with AutoCAD.

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