AutoCAD uses two commands for refreshing your drawing display: drawing regeneration (Regen) and Redraw. Each command serves a particular purpose, although it may not be clear to a new user.

To better understand the difference between Regen and Redraw, it helps to know that AutoCAD stores drawing data in two ways:

As you draw, AutoCAD starts to build an accurate, core database of objects and their properties. At the same time, it creates a simpler database that it uses just to display the drawing quickly. AutoCAD uses this second database to allow quick manipulation of the display of your drawing. For the purposes of this discussion, I'll call this simplified database the virtual display because it's like a computer model of the overall display of your drawing. This virtual display is in turn used as the basis for what is shown in the drawing area. When you issue a Redraw command, you're telling AutoCAD to reread this virtual display data and display that information in the drawing area. A Regen command, on the other hand, tells AutoCAD to rebuild the virtual display based on information from the core drawing database.

You may notice that the Pan Realtime and Zoom Realtime commands don't work beyond a certain area in the display. When you reach a point where these commands seem to stop working, you've come to the limits of the virtual display data. To go beyond these limits, AutoCAD must rebuild the virtual display data from the core data; in other words, it must regenerate the drawing. You can usually do this by zooming out to the extents of the drawing.

Sometimes, when you zoom in to a drawing, arcs and circles may appear to be faceted instead of smooth curves. This faceting is the result of AutoCAD's virtual display simplifying curves to conserve memory. You can force AutoCAD to display the curves in a smoother curve by typing RE

Controlling Display Smoothness

As you work in AutoCAD, you may notice that linetypes sometimes appear continuous even when they're supposed to be dotted or dashed. You may also notice that arcs and circles occasionally appear to be segmented lines although they're always plotted as smooth curves. A command called Viewres controls how smoothly linetypes, arcs, and circles are displayed in an enlarged view. The lower the Viewres value, the fewer the segments and the faster the redraw and regeneration. However, a low Viewres value causes noncontinuous linetypes, such as dashes or center lines, to appear continuous, especially in drawings that cover very large areas (for example, civil site plans).

Finding a Viewres value that best suits the type of work you do will take some experimentation. The default Viewres setting is 1000. You can try increasing the value to improve the smoothness of arcs and see if a higher value works for you. Enter Viewres

Saving Views

Another way to control your views is by saving them. You might think of saving views as a way of creating a bookmark or a placeholder in your drawing.

For example, a few walls in the Plan drawing aren't complete. To add the lines, you'll need to zoom in to the areas that need work, but these areas are spread out over the drawing. AutoCAD lets you save views of the areas you want to work on and then jump from saved view to saved view. This technique is especially helpful when you know you'll often want to return to a specific area of your drawing.

You'll see how to save and recall views in the following set of exercises. Here's the first one:

1. Click All from the Zoom flyout on the View tab's Navigate panel, or type Z

   

2. Choose Named Views from the View tab's Views panel or type V

   
   

   Figure 7.4. The View Manager dialog box

Managing Saved Views

In the View Manager dialog box, you can call up an existing view (Set Current), create a new view (New), or get detailed information about a view. You can also select from a set of predefined views that include orthographic and isometric views of 3D objects. You'll learn more about these options in Chapter 21.

1. Make sure the Current option is selected in the list to the left, and then click the New button to open the New View dialog box (Figure 7.5). You'll notice some options related to the User Coordinate System (UCS) plus an option called View Category. You'll get a chance to look at the UCS in Chapters 21 and 22. The View Category option relates to the Sheet Set feature described in Chapter 30. Other options, including Visual Style, Background, and Boundary, give you control over the appearance of the background and layout of a saved view. For now, you'll concentrate on creating a new view.

   

   Figure 7.5. The New View / Shot Properties dialog box

2. Click the Define Window radio button. The dialog boxes momentarily disappear, and the Dynamic input display turns on.

3. At the Specify first corner: prompt, click two points to place a selection window around the area around the elevator lobby, as shown in Figure 7.6. Notice that the display changes so that the white area shows the area you selected. If you aren't satisfied with the selection area, you can place another window in the view.

   

   Figure 7.6. Select this area for your saved view.

4. When you're satisfied with your selection, press

   

5. Click the View Name input box, and type Elevator Lobby for the name of the view you just defined.

6. Click the OK button. The New View dialog box closes, and you see Elevator Lobby in the Views list.

7. Click OK to close the View Manager dialog box.

8. Let's see how to recall the view that you've saved. From the View tab's Views panel, click the 3D Navigation drop-down list, and select Elevator Lobby.

   

Your view changes to a close-up of the area you selected in step 5. You can also open the View dialog box (enter V

If you need to make adjustments to a view after you've created it, you can do so by following these steps: Right-click the view name in the View Manager dialog box, select Edit Boundaries, and then select a window as you did in steps 5 and 6.

Repeat the Last Command

Remember that when no command is active, you can right-click the Command window and then select Recent Commands to repeat a recently issued command. You can also right-click the drawing area when AutoCAD is idle and repeat the last command.

If you prefer, you can use the keyboard to invoke the View command and thus avoid all the dialog boxes:

1. Click Extents from the Zoom flyout on the View tab's Navigate panel, or type Z

   

2. Enter –View

   

3. At the Enter view name to save: prompt, enter Overall

   

4. Save the Plan file to disk.

As you can see, this is a quick way to save a view. With the name Overall assigned to this view, you can easily recall it at any time. (Choosing the Zoom flyout's All option gives you an overall view too, but it may zoom out too far for some purposes, or it may not show what you consider an overall view.)

Opening a File to a Particular View

The Select File dialog box contains a Select Initial View check box. If you open an existing drawing with this option selected, you're greeted with a Select Initial View dialog box just before the opened file appears on the screen. This dialog box lists any views saved in the file. You can then go directly to a view by double-clicking the view name. If you've saved views and you know the name of the view you want, using Select Initial View saves time when you're opening large files.

As mentioned earlier, you may want to turn off certain layers to plot a drawing containing only selected layers. But even when layers are turned off, AutoCAD still takes the time to redraw and regenerate them. The Layer Properties Manager offers the Freeze option; this acts like the Off option, except that Freeze causes AutoCAD to ignore frozen layers when redrawing and regenerating a drawing. By freezing layers that aren't needed for reference or editing, you can reduce the time AutoCAD takes to perform regens. This can be helpful in large, multi-megabyte files.

Be aware, however, that the Freeze option affects blocks in an unusual way. Try the following exercise to see firsthand how the Freeze option makes entire blocks disappear:

Even though none of the objects in the unit blocks were drawn on the Plan1 layer, the entire contents of the blocks assigned to the Plan1 layer are frozen when Plan1 is frozen. Another way to freeze and thaw individual layers is by clicking the Freeze/Thaw icon (which looks like a sun) in the Layer Control drop-down list in the Home tab's Layers panel.

You don't really need the Plan1 layer frozen. You froze it to see the effects of Freeze on blocks. Do the following to turn Plan1 back on:

The previous exercise showed the effect of freezing on blocks. When a block's layer is frozen, the entire block is made invisible regardless of the layer assignments of the objects contained in the block.

Keep in mind that when blocks are on layers that aren't frozen, the individual objects that are part of the block are still affected by the status of the layer to which they're assigned. This means that if some objects in a block are on a layer called Wall and the Wall layer is turned off or frozen, then those objects become invisible. Objects with the block that aren't on the layer that is off or frozen remain visible.

It's always a good idea to provide a separate layer for hatch patterns. By doing so, you can turn them off if you need to. For example, the floor paving pattern might be displayed in one drawing but turned off in another so it won't distract from other information.

In the following exercises, you'll set up a layer for a hatch pattern representing floor tile and then add that pattern to your drawing. This will give you the opportunity to learn the different methods of creating and controlling hatch patterns.

Follow these steps to set up the layer:

Now that you've set up the layer for the hatch pattern, you can place the pattern in the drawing:

The Hatch And Gradient dialog box lets you first define the boundary in which you want to place a hatch pattern. You do this by clicking a location inside the boundary area, as in step 6. AutoCAD finds the boundary for you. Many options give you control over how a hatch boundary is selected. For details, see the section "Understanding the Boundary Hatch Options" later in this chapter.

In the previous exercise, you placed the hatch pattern in the bathroom without regard for the location of the lines that make up the pattern. In most cases, however, you'll want accurate control over where the lines of the pattern are placed.

By default, hatch patterns use the drawing origin (0,0) as the pattern origin. This means that the corner of the hatch pattern starts at the 0,0 coordinate, even though the pattern is only displayed in the area you select. The Hatch And Gradient dialog box offers a set of options that give you control over the hatch origin, thereby allowing you to control the exact positioning of the hatch pattern in the area you're hatching. This can be crucial for laying out tile patterns on a floor or ceiling, for example.

The following exercise guides you through the process of placing a hatch pattern accurately, using the example of adding floor tile to the kitchenette. You'll start by drawing the area of the tile pattern and then go on to select a pattern for the tile:

The Hatch Pattern Palette dialog box opens. This dialog box lets you select a predefined pattern from a graphic that shows what the pattern looks like.

If you know the name of the pattern you want, you can select it from the Pattern drop-down list in the Hatch And Gradient dialog box.

You've selected the hatch pattern. The next thing is to place the pattern in the drawing. First, you'll select the location for the hatch pattern, and then you'll experiment with the origin settings to see how they affect the positioning of the pattern:

Notice that each tile is shown whole; none of the tiles are cut off as in the bathroom example. This is the result of using the Specified Origin option and the Default To Boundary Extents option in the Hatch And Gradient dialog box.

The Specified Origin option gives you access to a number of hatch pattern features. In the previous exercise, you used the Default To Boundary Extents feature, which is best suited to rectangular areas. This option assumes you're hatching a rectangular area, and it lets you place the boundary hatch origin in one of the four corners of a rectangle or directly in the center. The default option is Bottom Left, as shown in the drop-down list. The graphic to the right of the list also shows a cross where the origin is located in a rectangular area.

The Click To Set New Origin option lets you select a point in your drawing to specify the hatch origin. When you click this option, the dialog box temporarily closes to allow you to select a point.

Finally, the Store As Default Origin option lets you save your selected origin as the default origin for future hatch patterns in the current drawing.

In the previous exercise, you used a predefined hatch pattern. Figure 7.11 shows you all the patterns available. You can also create your own custom patterns, as described in Chapter 28.

Figure 7.11. Predefined hatch patterns available in AutoCAD

The predefined patterns with the AR prefix are architectural patterns that are drawn to full scale. In general, you should leave their Scale settings at 1. You can adjust the scale after you place the hatch pattern by using the Properties palette, as described later in this chapter

In the next exercise, you'll use this updated 07a-unit file to update all the units in the Plan file.

As you progress through a design project, you make countless revisions. With traditional drafting methods, revising a drawing such as the studio apartment floor plan takes a good deal of time. If you change the bathroom layout, for example, you have to erase every occurrence of the bathroom and redraw it 16 times. With AutoCAD, on the other hand, revising this drawing can be a quick operation. You can update the studio unit you just modified throughout the overall plan drawing by replacing the current Unit block with the updated Unit file. AutoCAD can update all occurrences of the Unit block. The following exercise shows how this is accomplished.

For this exercise, remember that the blocks representing the units in the 07b-plan and 07b-plan-metric files are named 07a-unit and 07a-unit-metric:

Nested blocks must be updated independently of the parent block. For example, if you modified the Toilet block while editing the 07a-unit file and then updated the 07a-unit drawing in the 07b-plan file, the old Toilet block wouldn't be updated. Even though the toilet is part of the 07a-unit file, it's still a unique, independent block in the Plan file, and AutoCAD won't modify it unless specifically instructed to do so. In this situation, you must edit the original Toilet block and then update it in both the Plan and Unit files.

Figure 7.12. The Plan drawing with the tile pattern

Replacing Blocks

If you want to replace one block with another in the current file, type –Insert

Also, block references and layer settings of the current file take priority over those of the imported file. For example, if a file to be imported has layers of the same name as the layers in the current file but those layers have color and linetype assignments that are different from the current file's, the current file's layer color and linetype assignments determine those of the imported file. This doesn't mean, however, that the imported file on disk is changed; only the inserted drawing is affected.

You may have noticed the Associative option in the Hatch And Gradient dialog box. When this radio button is selected, AutoCAD creates an associative hatch pattern. Associative hatches adjust their shapes to any changes in their associated boundary, hence the name. The following exercise demonstrates how this works.

Suppose you want to enlarge the tiled area of the kitchen by one tile. Here's how it's done:

The Associative feature of hatch patterns can save time when you need to modify your drawing, but you need to be aware of its limitations. A hatch pattern can lose its associativity when you do any of the following:

These situations frequently arise when you edit an unfamiliar drawing. Often, boundary objects are placed on a layer that is off or frozen, so the boundary objects aren't visible. Also, the hatch pattern might be on a layer that is turned off, and you proceed to edit the file not knowing that a hatch pattern exists. When you encounter such a file, take a moment to check for hatch boundaries so you can deal with them properly.

Like everything else in a project, a hatch pattern may eventually need to be changed in some way. Hatch patterns are like blocks in that they act like single objects. You can explode a hatch pattern to edit its individual lines. The Properties palette contains most of the settings you'll need to make changes to your hatch patterns. But the most direct way to edit a hatch pattern is to use the Hatch Edit dialog box.

Editing Hatch Patterns from the Hatch Edit Dialog Box

Follow these steps to modify a hatch pattern by using the Hatch Edit dialog box:

1. 

2. Press the Esc key to clear any grip selections that may be active from earlier exercises.

3. Double-click the hatch pattern in the kitchen to open the Hatch Edit dialog box. It's the same as the Hatch And Gradient dialog box.

   When a Double-click Doesn't Open the Properties Palette

   When you double-click a hatch pattern, you don't get the typical Properties palette. Double-clicking complex objects such as text, blocks, attributes, and hatch patterns opens a dialog box in which you can edit the object in a more direct way. You can still access the Properties palette for any object by right-clicking the object and choosing Properties from the shortcut menu.

4. Click the Browse button to the right of the Pattern drop-down list to open the Hatch Pattern Palette dialog box at the Other Predefined tab (Figure 7.14).

   

   Figure 7.14. The Other Predefined tab in the Hatch Pattern Palette dialog box

5. Locate and double-click the pattern named AR-BRSTD. It's the pattern that looks like a brick wall. The Hatch Pattern Palette dialog box closes, and you see the AR-BRSTD hatch pattern in the Swatch field.

6. Click OK to accept the change to the hatch pattern. The AR-BRSTD pattern appears in place of the original parquet pattern.

7. Exit and save your file.

In this exercise, you were able to change the hatch just by double-clicking it. Although you changed only the pattern type, other options are available. You can, for example, modify a predefined pattern to a user-defined one by selecting User Defined from the Type listing in the Hatch Edit dialog box.

You can then enter angle and spacing values for your hatch pattern in the spaces provided in the Hatch Edit dialog box.

The other items in the Hatch Edit dialog box duplicate some of the options in the Hatch And Gradient dialog box. They let you modify the individual properties of the selected hatch pattern. The upcoming section, "Understanding the Boundary Hatch Options," describes these other properties in detail.

Editing Hatch Patterns from the Properties Palette

If you prefer, you can use the older method to edit a hatch pattern. To open the Properties palette, right-click a pattern and choose Properties from the shortcut menu. The Properties palette displays a Pattern category, which offers a Pattern Name option (Figure 7.15).

Figure 7.15. The Pattern category in the Properties palette

When you click this option, an ellipsis button appears, enabling you to open the Hatch Pattern Palette dialog box, just as in step 4 of the previous exercise. You can then select a new pattern from the dialog box. The Type option in the Properties palette lets you change the type of hatch pattern from Predefined to User Defined or Custom.

Take a Break

If you're working through the tutorial in this chapter, this would be a good place to take a break or stop. You can pick up the next exercise in the section "Attaching a Drawing as an External Reference" at another time.

AutoCAD's Boundary Hatch command has a fair amount of "intelligence." As you saw in an earlier exercise, it was able to detect not only the outline of the floor area, but also the outline of the toilet seat that represents an island in the pattern area. If you prefer, you can control how AutoCAD treats these island conditions and other situations by selecting options available when you click the More Options button in the lower-right corner of the Hatch And Gradient dialog box.

This button expands the dialog box to show additional hatch options (Figure 7.16).

Figure 7.16. The additional hatch options

You may have noticed that one of the hatch patterns offered is a solid. The solid hatch pattern lets you apply a solid color instead of a pattern to a bounded area. AutoCAD also offers a set of gradient patterns that let you apply a color gradient to an area.

You can apply a gradient to an area by using the same method you used to apply a hatch pattern, but instead of using the Hatch tab of the Hatch And Gradient dialog box, you use the Gradient tab to select a gradient pattern (Figure 7.17).

Figure 7.17. The Gradient Shading feature

Choosing a Gradient Color

Instead of offering hatch patterns, the Gradient tab offers a variety of gradient patterns. It also lets you control the color of the gradient. For example, if you want to set the gradient between shades of blue, you can click the One Color radio button and then double-click the blue color swatch at the top of the dialog box.

When you double-click the color swatch, the Select Color dialog box opens, offering a palette of True Color options (Figure 7.18).

Figure 7.18. The True Color options in the Select Color dialog box

You can then select the color you want for the gradient. On the Gradient tab of the Hatch And Gradient dialog box, the Shade/Tint slider just below the Two Color radio button lets you control the shade of the single-color gradient.

Here are a few tips on using the Boundary Hatch feature:

Suppose you're working on a plan in which you're constantly repositioning equipment and furniture or you're in the process of designing the floor covering. You might be a little hesitant to place a hatch pattern on the floor because you don't want to have to rehatch the area each time you move a piece of equipment or change the flooring. You have two options in this situation: You can use Boundary Hatch's associative capabilities to include the furnishings in the boundary set, or you can use the Display Order feature.

Overlapping Objects with Draw Order

The Draw Order feature lets you determine how objects overlap. In the space-planning example, you can create furniture by using a solid hatch to indicate horizontal surfaces (see Figure 7.19).

Figure 7.19. Using Draw Order to create an overlapping effect over a hatch pattern

How to Match a Hatch Pattern and Other Properties Quickly

Another tool to help you edit hatch patterns is Match Properties, which is similar to Format Painter in the Microsoft Office system. This tool lets you change an existing hatch pattern to match another existing hatch pattern. Here's how to use it:

1. Type Matchprop

   

2. Click the source hatch pattern you want to copy.

3. Click the target hatch pattern you want to change. The target pattern changes to match the source pattern.

The Match Properties tool transfers other properties as well, such as layer, color, and linetype settings. You can select the properties that are transferred by opening the Property Settings dialog box.

To open this dialog box, type S

You can then place the furniture on top of a floor-covering pattern and the pattern will be covered and hidden by the furniture. Here's how to do that. (These steps aren't part of the regular exercises of this chapter. They're shown here as general guidelines when you need to use the Draw Order feature.)

1. Draw the equipment outline, and make sure the outline is a closed polygon.

2. 

3. In the Hatch And Gradient dialog box, make sure that Send Behind Boundary is selected in the Draw Order drop-down list.

4. Complete the rest of the hatch pattern.

5. After you've finished placing the hatch, turn the outline and solid hatch into a block, or use the Group command to group them.

6. Click the Bring To Front tool form the Draworder flyout on the Home tab's Modify panel, and then select the equipment.

   

7. Press

   

After you take these steps, you can place the equipment over a hatched floor pattern, and the equipment will appear to rest on top of the pattern. If you create a floor pattern after you create the equipment, click the Send To Back option in the Draworder flyout to move the pattern to the back of the display order. You can also change the display order of objects relative to other objects.

The Draworder options are all part of the Draworder command. As an alternative to the menu, you can type Draworder

Enter object ordering option
[Above objects/Under objects/Front/Back] <Back>:

For example, the equivalent of choosing the Send To Back tool from the Draworder flyout is entering Draworder

If you need to white out an area of a hatch pattern to make text more readable, you can use a solid hatch along with the Display Order option to block out areas behind text.

You've had a detailed look at hatch patterns and fills in this section. Remember that you can also use the Tool palettes to help organize and simplify access to your favorite hatch patterns, or you can use the patterns already available in the Tool palettes. The patterns in the Tool palettes can be edited and manipulated in the same way as described in this chapter. If you want to know how to make full use of the Tool palettes, check out the discussion on the AutoCAD DesignCenter in Chapter 29.

The next exercise shows how to use an Xref in place of an inserted block to construct the studio apartment building. You'll first create a new unit file by copying the old one. Then you'll bring a new feature, the External References palette, to the screen. Follow these steps to create the new file:

Now you're ready to use the External References palette:

You now have a drawing that looks like the 07b-plan.dwg file you worked with earlier in this chapter, but instead of blocks that are detached from their source file, you have a drawing composed of Xrefs. These Xrefs are the actual Unitxref.dwg file, and they're loaded into AutoCAD at the same time that you open the Planxref.dwg file. An icon in the lower-right corner of the AutoCAD window tells you that the current drawing contains Xrefs.

Next, you'll modify the Unitxref.dwg file and see the results in the Planxref.dwg file:

The Open option in the External References palette performs the same function as the Xopen command and the Open Xref option in the shortcut menu. To use this option, select and right-click the Xref files from the list box in the External References palette and then click Open.

Be aware that when an Xref has been modified, the Manage Xrefs icon at lower right in the AutoCAD window changes to show an exclamation point. This alerts you to changes in an Xref in the current drawing.

Click the Manage Xrefs icon to open the External References palette. The Xref that has been changed is indicated by a warning icon in the Status column of the list box.

You can then select the Xref that needs to be updated, right-click, and choose the Reload option from the shortcut menu to reload the selected Xref. You can also select multiple Xrefs if more than one needs updating.

Here you saw how an Xref file is updated in a different way than a block. Because Xrefs are loaded along with the drawing file that contains them, the containing file, which in this case was the Planxref file, automatically displays any changes made to the Xref when it's opened. Also, you avoid having to update nested blocks because AutoCAD updates nested Xrefs as well as non-nested Xrefs. When an Xref is modified while you're editing a file, you're alerted to the change through the Xref icon located in the lower-right corner of the AutoCAD window. You can click the balloon message that appears from that icon to update any modified Xrefs.

Here are a few other differences between Xrefs and inserted blocks that you'll want to keep in mind:

Importing Blocks, Layers, and Other Named Elements from External Files

You can use the Xbind command to import blocks and other named elements from another file. First, use the External References palette to cross-reference a file; type Xbind at the Command prompt. In the Xbind dialog box, click the plus sign next to the Xref filename, and then select Block. Locate the name of the block you want to import, click the Add button, and click OK. Finally, open the External References palette, select the Xref filename from the list, right-click, and select Detach to remove the Xref file. The imported block remains as part of the current file. (See Chapter 15 for details on importing named elements.) You can also use the AutoCAD DesignCenter to import named elements from external files. DesignCenter is described in Chapter 29.

The Tool Palettes window gives you access to frequently used blocks and hatch patterns that reside in other drawings. You can open the Tool palettes by clicking the Tool Palettes tool in the View tab's Palettes panel.

In the standard AutoCAD installations, the Tool Palettes window is configured with sample 3D commands, blocks, and hatch patterns that you can drag and drop into your current drawing. Select a tab for the Tool palette that contains the block or pattern you want, and then click and drag the item into your drawing. In the case of hatch patterns, click and drag the pattern into an area that is bounded on all sides by objects. When you're ready to customize the Tool Palettes window, you do so by clicking and dragging objects or tools into a new or existing palette. See Chapter 28 for more on customizing tool palettes.

Many other features are unique to external reference files. Let's briefly look at some of the other options in the External References palette.

The Attach External Reference Dialog Box

The Attach External Reference dialog box, shown in Figure 7.21 earlier in this chapter, offers these options:

Browse

Opens the Select Reference File dialog box to enable you to change the file you're importing as an Xref.

Attachment

Tells AutoCAD to include other Xref attachments that are nested in the selected file.

Overlay

Tells AutoCAD to ignore other Xref attachments that are nested in the selected file. This avoids multiple attachments of other files and eliminates the possibility of circular references (referencing the current file into itself through another file).

Path Type

Offers options for locating Xrefs. Xref files can be located anywhere on your system, including network servers. For this reason, you can easily lose links to Xrefs either by moving them or by rearranging file locations. To help you manage Xrefs, the Path Type option offers three options: Full Path, Relative Path, and No Path. Full Path retains the current full path. Relative Path maintains paths in relation to the current drawing. The current drawing must be saved before using the Relative Path option. The No Path option is for drawings in which Xrefs are located in the same folder as the current drawing or in the path specified in Support File Search Path in the Files tab of the Options dialog box (choose Options from the Application menu).

Specify On-Screen

Appears in three places. It gives you the option to enter insertion point, scale factors, and rotation angles in the dialog box or in the Command window, in a way similar to inserting blocks. If you clear this option for any of the corresponding parameters, the parameters change to allow input. If they're selected, you're prompted for those parameters after you click OK to close the dialog box. With all three Specify On-Screen check boxes cleared, the Xref is inserted in the drawing using the settings indicated in the dialog box.

Real World Scenario: External References in the San Francisco Main Library Project

Although these exercises demonstrate how Xrefs work, you aren't limited to using them in the way shown here. Perhaps one of the more common ways of using Xrefs is to combine a single floor plan with different title block drawings, each with its own layer settings and title block information. In this way, single-drawing files can be reused in several drawing sheets of a final construction document set. This helps keep data consistent across drawings and reduces the number of overall drawings needed.

This is exactly how Xrefs were used in the San Francisco Main Library drawings. One floor-plan file contained most of the main information for that floor. The floor plan was then used as an Xref in another file that contained the title block as well as additional information such as furnishings or floor finish reference symbols. Layer visibility was controlled in each title block drawing so only the data related to that drawing appeared.

Multiple Xref files were also used by segregating the structural column grid layout drawings from the floor-plan files. In other cases, portions of plans from different floors were combined into a single drawing by using Xrefs, as shown here.

Xrefs are frequently used to import large drawings for reference or backgrounds. Multiple Xrefs, such as a floor plan, column grid layout, and site-plan drawing, might be combined into one file. One drawback to multiple Xrefs in earlier versions of AutoCAD was that the entire Xref was loaded into memory even if only a small portion of it was used for the final plotted output. For computers with limited resources, multiple Xrefs could slow the system to a crawl.

AutoCAD 2010 offers two tools that help make display and memory use more efficient when using Xrefs: the Xclip command and the Demand Load option in the Options dialog box.

Clipping Views

You can clip blocks and multiple Xrefs as well. You can also specify a front and back clipping distance so that the visibility of objects in 3D space can be controlled. You can define a clip area by using polylines or spline curves, although curve-fitted polylines revert to decurved polylines. (See Chapter 19 for more on polylines and spline curves.)

Controlling Xref Settings in the Options Dialog Box

The External References (Xrefs) group in the Open And Save tab of the Options dialog box offers some tools to help you manage memory use and other features related to Xrefs. If you're working on large projects with others in a workgroup, you should be aware of these settings and what they do.

The Demand Load Xrefs drop-down list offers three settings: Disabled, Enabled, and Enabled With Copy. Demand Load is set to Enable With Copy by default in the standard AutoCAD drawing setup. In addition to reducing the amount of memory an Xref consumes, Demand Load prevents other users from editing the Xref while it's being viewed as part of your current drawing. This helps aid drawing version control and drawing management. The Enabled With Copy option creates a copy of the source Xref file and then uses the copy, thereby enabling other AutoCAD users to edit the source Xref file.

Demand loading improves performance by loading only the parts of the referenced drawing that are needed to regenerate the current drawing. You can set the location for the Xref copy in the Files tab of the Options dialog box under Temporary External Reference File Location.

Two other options are also available in the Options dialog box:

Retain Changes To Xref Layers

Instructs AutoCAD to remember any layer color or visibility settings of Xrefs from one editing session to the next. In the standard AutoCAD settings, this option is on by default.

Allow Other Users To Refedit Current Drawing

Lets others edit the current drawing by choosing Edit Reference from the Insert tab's expanded Reference panel (Refedit). You'll learn about this command in the next section.

Figure 7.22. The first panel shows a polyline outline of the area to be isolated with Xclip. The second panel shows how the Xref appears after Xclip is applied. The last panel shows a view of the plan with the polyline's layer turned off.

Earlier, you saw that when you click an Xref, the External Reference tab appears. This tab offers several tools divided into three panels: Edit, Clipping, and Options. See Table 7.2 for a complete description of these tools.

In the previous exercises, you removed objects from the Kitchen block by using the Erase command. You can also move objects from a block or an Xref into the current drawing without erasing them. To do this, choose Remove From Working Set from the Insert tab's expanded Edit Reference panel while in the Refedit command. This removes the objects from the block or Xref without erasing them. Likewise, you can add new objects to the block or Xref by choosing Add To Working Set from the Insert tab's expanded Edit Reference panel. Both menu options invoke the Refset command, with different options applied.

To see how Refset works, try the following exercise:

Notice that the burners become grayer to show that they're removed from the working set. They remain as part of the Planxref drawing, but they're no longer part of the Kitchen block.

Now add a rectangle to the Kitchen block in place of the burners:

You can see that the burners have been replaced by the rectangle in all the other Xref units. The burners you moved are still there in the lower-left corner unit, but they have been removed from all the Xrefs. It's as if you extracted them from the block and placed them in the Plan drawing.

While you were using the Refedit command, any new objects you create are added to the working set automatically. When you drew the rectangle in step 1, for example, it was automatically included in the working set, which is the set of objects included in the block or Xref you're currently working on. You didn't have to specifically add it to the working set.

Figure 7.27. The Planxref drawing with the changes made to the Unitxref Xref

You've completed the exercises in this chapter, so you can exit AutoCAD without saving these changes.

The Reference Edit dialog box offers you the option to isolate specific blocks in the Xref by selecting them from the hierarchy list. You may have noticed the two radio button options: Automatically Select All Nested Objects and Prompt To Select Nested Objects. The default option, Automatically Select All Nested Objects, lets you select any object contained in the selected object in the hierarchy listing. If you select the Prompt To Select Nested Objects option, you're prompted to select objects on the screen before the Edit Reference panel appears.

In addition to the options you used in the exercises, the Reference Edit dialog box also includes the Settings tab with some options (Figure 7.28).

Figure 7.28. The Settings tab of the Reference Edit dialog box