The Block Definition dialog box offers several options that can help make using blocks easier. If you're interested in these options, take a moment to review the Block Definition dialog box as you read the descriptions. If you prefer, you can continue with the tutorial and come back to this section later.

You've already seen how the Name option lets you enter a name for your block. AutoCAD doesn't let you complete the block creation until you enter a name.

You've also seen how to select a base point for your block. The base point is like the grip of the block: It's the reference point you use when you insert the block back into the drawing. In the exercise, you used the Pick Point option to indicate a base point, but you also have the option to enter X, Y, and Z coordinates just below the Pick Point option. In most cases, however, you'll want to use the Pick Point option to indicate a base point that is on or near the set of objects you're converting to a block.

The Objects group of the Block Definition dialog box lets you select the objects that make up the block. You use the Select Objects button to visually select the objects you want to include in the block you're creating. The QuickSelect button to the right of the Select Objects button lets you filter out objects based on their properties. You'll learn more about QuickSelect in Chapter 15. Once you select a set of objects for your block, you'll see a thumbnail preview of the block's contents in the upper-right corner of the Block Definition dialog box.

Other options in the Objects group and Settings group let you specify what to do with the objects you're selecting for your block. Table 4.1 shows a list of those other options and what they mean.

In step 7 in the previous section, you can see the tub rotate as you move the cursor. You can pick a point to fix the block in place, or you can enter a rotation value. This is the result of selecting the Specify On-Screen option in the Insert dialog box. You may find that you want the Rotation group's Specify On-Screen option turned on most of the time to enable you to adjust the rotation angle of the block while you're placing it in the drawing.

The other options in the Insert dialog box that you didn't use are the Scale group options. These options let you scale the block to a different size. You can scale the block uniformly, or you can distort the block by individually changing its X, Y, or Z scale factor. With the Specify On-Screen option unchecked, you can enter specific values in the X, Y, and Z text boxes to stretch the block in any direction. If you turn on the Specify On-Screen option, you can visually adjust the X, Y, and Z scale factors in real time. Although these options aren't used often, they can be useful in special situations when a block needs to be stretched one way or another to fit in a drawing.

You aren't limited to scaling or rotating a block when it's being inserted into a drawing. You can always use the Scale or Rotate tools or modify an inserted block's properties to stretch it in one direction or another. This exercise shows you how this is done:

If a block is created with the Scale Uniformly option turned on in the Block Definition dialog box, you can't scale the block in just one axis as shown in the previous exercise. You can only scale the block uniformly in all axes.

You've just seen how you can modify the properties of a block by using the Properties palette. In the exercise, you changed the X scale of the Toilet block, but you could have just as easily changed the Y value. You may have noticed other properties available in the Properties palette. You'll learn more about those properties as you work through this chapter.

You've seen how you can turn a drawing into a symbol, known as a block in AutoCAD. Now let's see how you can use an existing drawing file as a block.

You need a door into the bathroom. Because you've already drawn a door and saved it as a file, you can bring the door into this drawing file and use it as a block:

The Command prompt appears, but nothing seems to happen to the drawing. This is because when you enlarged the door, you also enlarged the distance between the base point and the object. This brings up another issue to be aware of when you're considering using drawings as symbols: All drawings have base points. The default base point is the absolute coordinate 0,0, otherwise known as the origin, which is located in the lower-left corner of any new drawing. When you drew the door in Chapter 2, you didn't specify the base point. When you try to bring the door into this drawing, AutoCAD uses the origin of the door drawing as its base point (see Figure 4.6).

Figure 4.6. By default, a drawing's origin is also its insertion point. You can change a drawing's insertion point by using the Base command.

Because the door appears outside the bathroom, you must first choose All from the Zoom flyout on the View tab's Navigate panel to show more of the drawing and then use the Move command on the Modify panel to move the door to the right-side wall of the bathroom. Let's do this now:

Because the door is an object that you'll use often, it should be a common size so you don't have to specify an odd value every time you insert it. It would also be helpful if the door's insertion base point were in a more convenient location; that is, a location that would let you place the door accurately within a wall opening. Next you'll modify the Door block to better suit your needs.

One way to modify a block is to break it down into its components, edit them, and then turn them back into a block. This is called redefining a block. If you redefine a block that has been inserted in a drawing, each occurrence of that block in the current file changes to reflect the new block definition. You can use this block-redefinition feature to make rapid changes to a design.

To separate a block into its components, use the Explode command:

You can simultaneously insert and explode a block by clicking the Explode check box in the lower-left corner of the Insert dialog box.

Now you can edit the individual objects that make up the door, if you desire. In this case, you want to change only the door's insertion point because you've already made it a more convenient size. You'll turn the door back into a block, this time using the door's lower-left corner for its insertion base point:

The Select Objects and Pick Point buttons appear in other dialog boxes. Make note of their appearance, and remember that when you select them, the dialog box temporarily closes to let you select points or objects and otherwise perform operations that require a clear view of the drawing area.

In step 7, you received a warning message that you were about to redefine the existing Door block. But originally, you inserted the door as a file, not as a block. Whenever you insert a drawing file by using the Insert Block tool, the inserted drawing automatically becomes a block in the current drawing. When you redefine a block, however, you don't affect the drawing file you imported. AutoCAD changes only the block in the current file.

You've just redefined the door block. Now place the door in the wall of the room:

Figure 4.9. The bathroom, first with the tub and then with the toilet inserted

To mirror an object using grips, first be sure the Grips feature is on. (It's usually on by default.) Select the objects to mirror, click a grip, and right-click. Select Mirror from the shortcut menu; then, indicate a mirror axis with the cursor.

Next you'll see how you can update an external file with a redefined block.

You've seen that, with little effort, you can create a symbol and place it anywhere in a file. Suppose you want to use this symbol in other files. When you create a block by using the Block command, the block exists in the current file only until you specifically instruct AutoCAD to save it as a drawing file on disk. When you have an existing drawing that has been brought in and modified, such as the door, the drawing file on disk associated with that door isn't automatically updated. To update the Door file, you must take an extra step and use the Export option on the Application menu. Let's see how this works.

Start by turning the Tub and Toilet blocks into individual files on disk:

If you prefer, you can skip step 2 and instead, in step 3, enter the full filename including the .dwg extension, as in Tub.dwg.

The Tub block is now saved as a file.

Options for Saving Blocks

AutoCAD gives you the option to save a block's file under the same name as the original block or save it with a different name. Usually, you'll want to use the same name, which you can do by entering an equal sign (=) after the prompt.

Normally, AutoCAD saves a preview image with a file. This enables you to preview a drawing file before opening it. Preview images aren't included with files that are exported with the Export

The Wblock command does the same thing as choosing Export

In this exercise, you typed the Wblock command at the Command prompt instead of choosing Export

So far you've used the Block tool to create symbols, and you've used the Export and Wblock commands to save those symbols to disk. As you can see, you can create symbols and save them at any time while you're drawing. You've made the tub and toilet symbols into drawing files that you can see when you check the contents of your current folder.

However, creating symbols isn't the only use for the Block, Export, and Wblock commands. You can use them in any situation that requires grouping objects (though you may prefer to use the more flexible Object Grouping dialog box discussed later in this chapter). You can also use blocks to stretch a set of objects along one axis by using the Properties palette. Export and Wblock also enable you to save a part of a drawing to disk. You'll see instances of these other uses of the Block, Export, and Wblock commands throughout the book.

Block, Export, and Wblock are extremely versatile commands and if used judiciously, can boost your productivity and simplify your work. If you aren't careful, however, you can get carried away and create more blocks than you can track. Planning your drawings helps you determine which elements will work best as blocks and recognize situations in which other methods of organization are more suitable.

Another way of using symbols is to use AutoCAD's external reference capabilities. External reference files, known as Xrefs, are files inserted into a drawing in a way similar to how blocks are inserted. The difference is that Xrefs don't become part of the drawing's database. Instead, they're loaded along with the current file at startup time. It's as if AutoCAD opens several drawings at once: the main file you specify when you start AutoCAD and the Xrefs associated with the main file.

By keeping the Xrefs independent from the current file, you make sure that any changes made to the Xrefs automatically appear in the current file. You don't have to update each inserted copy of an Xref. For example, if you use the Attach tool on the Insert tab's Reference panel (discussed in Chapter 7) to insert the tub drawing and later you make changes to the tub, the next time you open the Bath file, you'll see the new version of the tub. Or if you have both the tub and the referencing drawing open and you change the tub, AutoCAD will notify you that a change has been made to an external reference. You can then update the tub Xref using the External Reference palette.

Xrefs are especially useful in workgroup environments, where several people are working on the same project. One person might be updating several files that have been inserted into a variety of other files. Before Xrefs were available, everyone in the workgroup had to be notified of the changes and had to update all the affected blocks in all the drawings that contained them. With Xrefs, the updating is automatic. Many other features are unique to these files. They're discussed in more detail in Chapters 7 and 12.

LT users have to use a slightly different method to create a group. If you're using AutoCAD 2010 LT, do the following:

Now, whenever you want to select the workstation, you can click any part of it to select the entire group. At the same time, you can still modify individual parts of the group—the desk, partition, and so on—without losing the grouping of objects.

Next you'll make copies of the original group and modify the copies. Figure 4.18 is a sketch of the proposed layout that uses the new workstations. Look carefully and you'll see that some of the workstations in the sketch are missing a few of the standard components that exist in the Station1 group. One pair of stations has a partition removed; another station has no desk.

Figure 4.18. A sketch of the new office layout

The exercises in this section show you how to complete your drawing to reflect the design requirements of the sketch.

Start by making a copy of the workstation:

You can also use the Direct Distance method by typing @

Next you'll use grips to mirror the first workstation copy:

Now that you've got the workstations laid out, you need to remove some of the partitions between the new workstations. If you had used blocks for the workstations, you would first need to explode the workstations that have partitions you want to edit. Groups, however, let you make changes without undoing their grouping.

Use these steps to remove the partitions:

Pickstyle is a system variable that controls how groups are selected. See Appendix B for more information about Pickstyle and other system variables.

Objects in a group aren't bound solely to that group. One object can be a member of several groups, and you can have nested groups.

Figure 4.21. The Object Grouping dialog box

AutoCAD LT users have a different set of options. See the next section, "Working with the LT Group Manager."

Table 4.2 gives a rundown of the options available in the Object Grouping dialog box.

If a group is selected, you can remove individual items from the selection with a Shift+click. In this way, you can isolate objects within a group for editing or removal without having to turn off groups temporarily.

You've seen how you can use groups to create an office layout. You can also use groups to help you keep sets of objects temporarily together in a complex drawing. Groups can be especially useful in 3D modeling when you want to organize complex assemblies together for easy selection.