Mastering AutoCAD 2005 and AutoCAD LT 2005

By now you should be familiar with the Pan and Zoom functions in AutoCAD. Many other tools can also help you get around in your drawing. In this section, you'll get a closer look at the different ways you can view your drawing.

Understanding Regeneration and Redrawing

AutoCAD uses two methods for refreshing your drawing display: the drawing regeneration, or regen, and the redraw . Each method serves a particular purpose, though they 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:

• In a database of highly accurate coordinate information that is part of the properties of objects in your drawing

• In a simplified database used just for the display of the objects in your drawing

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 is 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 are telling Auto- CAD to reread this virtual display data and display that information in the drawing area. A Regen command, on the other hand, causes AutoCAD to rebuild the virtual display based on information from the core drawing database.

As you edit drawings, you might find that some lines in the display disappear or otherwise appear corrupted. Redraw will usually restore such distortions. In earlier versions of AutoCAD, the Blip- mode system variable was turned on by default, causing markers called blips to appear wherever points were selected. Redraw was, and still is, useful in clearing the screen of these blips.

Regens are used less frequently and are brought to bear when you change settings and options that have a global effect on a drawing, such as a line-type scale, layer color , or text style. (You'll learn more about text styles in Chapter 8.) In fact, in many situations, regens are performed automatically when such changes occur. You usually don't have to issue the Regen command on your own, except in certain situations.

Regens can also occur when you select a view of a drawing that is not currently included as part of the virtual display. The virtual display contains display data for a limited area of a drawing. If you zoom or pan to a view outside that virtual display area, a regen occurs.

In AutoCAD R13 and earlier, regens were to be avoided as much as possible, especially in large files. A regen on a very large file could take several minutes to complete. Today, with faster processors, large amounts of RAM, and a retooled AutoCAD, regens are not the problem they once were. Still, they can be annoying when you're working with large files, particularly if you are using an older

Pentium-based computer. For these reasons, it pays to understand the finer points of controlling regens so you can reduce their impact on complex drawings.

You can control how regens affect your work in three ways:

• By taking advantage of AutoCAD's many display- related tools

• By setting up AutoCAD so that regens do not occur automatically

• By freezing layers that do not need to be viewed or edited

You will explore these methods in the following sections.

Exploring Ways to Control AutoCAD's Display

Perhaps one of the easiest ways to avoid regens is by making sure you don't cross into an area of your drawing that falls outside the virtual display's area. If you use Pan Realtime and Zoom Realtime, you are automatically kept safely within the bounds of the display list. In this section, you'll be introduced to other tools that will help keep you within those boundaries.

Controlling Display Smoothness

You can turn the virtual display on or off by using the Viewres command. The Viewres setting is on by default and, for the most part, should remain on. You can turn it off by typing Viewres No at the command prompt. However, I don't recommend this. With Viewres off, a regen occurs every time you use Pan or Zoom to change your view.

The Viewres command also controls the smoothness of line types, arcs, and circles when they appear in an enlarged view. With Viewres turned on, line types sometimes appear as continuous, even when they are supposed to be dotted or dashed. You might have noticed in previous chapters that on- screen arcs appear to be segmented lines, although they are always plotted as smooth curves. You can adjust the Viewres value to control the number of segments an arc appears to have: the lower the value, the fewer the segments and the faster the redraw and regeneration. However, a low Viewres value causes noncontinuous line types, such as dashes or center lines, to appear as continuous, especially in drawings that cover very large areas (for example, civil site plans).

Another way to accelerate screen redraw is to keep your drawing limits to a minimum area. If the limits are set unnecessarily high, AutoCAD might slow down noticeably. Also, make sure the drawing origin falls within the drawing limits.

Using the Aerial View

Let's take a tour of a tool that lets you navigate drawings representing very large areas. It's called the Aerial view:

1. Choose View   Aerial View on the menu bar to open the Aerial View window, as shown in Figure 6.4.

   Figure 6.4: The Aerial View window

2. Click the Aerial View window. As you move your mouse, notice what happens in the Auto- CAD window. Your view pans, following your motion in the Aerial View window. A bold rectangle in the Aerial View window representing your AutoCAD view moves with your cursor.

3. Click the Aerial View window again. Now as you move your cursor from left to right, the view in the AutoCAD window zooms in and out. This is the Zoom mode of the Aerial view. The rectangle in the Aerial View window now shrinks and expands as you move the cursor from left to right, indicating the size of the area being displayed in the AutoCAD window.

4. Move the cursor to the left so that the rectangle representing your AutoCAD view is about half the size of the overall view of the plan, and then right-click. Your AutoCAD view becomes fixed. Also notice that the magnification icon in the Aerial View toolbar becomes available.

So far, you've looked at ways to help you get around in your drawing while using a single view window. You can also set up multiple views of your drawing, called viewports. With viewports, you can display more than one view of your drawing at one time in the AutoCAD drawing area. For example, one viewport can display a close-up of the bathroom, another viewport can display the overall plan view, and yet another can display the unit plan.

When viewports are combined with AutoCAD's Paper Space feature, you can plot multiple views of your drawing. Paper Space is a display mode that enables you to "paste-up"multiple views of a drawing, much like a page layout program. To find out more about viewports and Paper Space, see Chapters 12 and 16.

As you can see from this exercise, you can cycle through the Pan and Zoom feature of the Aerial view by clicking the mouse. If you simply want to pan the view, you can right-click in step 2 of the previous exercise to fix your view in place. Or you can rapidly alternate between the Pan and Zoom modes by clicking the mouse until you've reached the location and view size you want.

The bold rectangle shows you exactly where you are in the overall drawing at any given time. This feature is especially useful in drawings of large areas that might take several pans to cross.

The Aerial View window is a great tool when you are working on a drawing that requires a lot of magnification in your zoomed-in views. It is also helpful when you need to maintain an overall view of a drawing as you work on closer detail. You might not find it helpful on drawings that don't require lots of magnification, such as the bathroom drawing you worked on in Chapters 3 and 4.

You were able to use the major features of the Aerial view in this exercise. Here are a few more features you can try on your own:

View   Zoom In Zooms in on the view defined by the bold rectangle in the Aerial view.

View   Zoom Out Zooms out of magnified view in the Aerial view.

View   Global Displays an overall view of your drawing in the Aerial View window. Global is like a View   Zoom   Extents option for the Aerial view.

Options   Auto Viewport Controls whether a selected viewport is automatically displayed in the Aerial View window. When this option is selected and a viewport becomes active, the Aerial View window automatically displays the contents of that viewport. (See Chapters 12 and 16 for more on viewports.)

Options   Dynamic Update Controls how AutoCAD updates the Aerial View window. When this setting is on, AutoCAD updates the Aerial view in real time as changes in the drawing occur. When this setting is off, changes in the drawing will not appear in the Aerial view until you click the Aerial View window.

Options   Realtime Zoom Controls whether the AutoCAD display is updated in real time as you zoom and pan in the Aerial View window.

Saving Views

Another way of controlling 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 are not 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. You could use the Aerial View window to view each area. There is, however, another way to edit widely separated areas: first, 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 will 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. Close the Aerial View window by clicking the Close button.

2. Choose View   Zoom   All or type Z A to get an overall view of the plan.

3. Choose View   Named Views or type V to open the View dialog box.

   Tip

   In the View dialog box, you can call up an existing view (Set Current), create a new view (New), or get detailed information about a view (Details). You can also click the Orthographic & Isometric Views tab to select from a set of predefined views. You'll learn more about these options in Chapter 15.

4. Make sure the Named Views tab is selected, and then click the New button to open the New View dialog box. 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 15 and 16. The View Category option relates to the Sheet Set feature described in Chapter 22. For now, you'll concentrate on creating a new view.

5. Click the Define Window radio button. Notice that the grayed button to the right, Define View Window, becomes available.

6. Click the Define View Window button. The dialog boxes momentarily disappear.

7. At the Specify first corner: prompt, click near the coordinate 26',40' (1715,1150 for metric users). You don't have to be exact because you are selecting view windows . Also, if you have Running Osnaps turned on, you might want to turn it off while selecting view windows .

8. At the Specify opposite corner: prompt, click a location near the coordinate 91',82' (2600,2500 for metric users). The dialog boxes reappear.

9. Click the View Name input box and type First for the name of the view you just defined.

   Warning

   In previous versions of AutoCAD, view names were converted to all uppercase. Beginning in AutoCAD 2000, view names are recorded as you type them, though they are not case sensitive.

10. Click the OK button. The New View dialog box closes , and you see First listed in the Name list.

11. Repeat steps 3 through 9 to define five more views, named Second, Third, and so on. Use Figure 6.5 as a guide for where to define the windows. Click OK when you are done.

    Figure 6.5: Save view windows in these locations for the Plan drawing.

Now let's see how to recall these views that you've saved:

1. With the View dialog box open, click First in the list of views.

   Tip	A quick way to restore saved views is to type “V R and then enter the name of the view you want to restore.

2. Click the Set Current button and then click OK. Your screen displays the first view you selected.

   Tip	To set the current view, you can also right-click the view name in the View dialog box. You can then choose Set Current, Delete, Details, or Rename from a shortcut menu.

3.  On the CD      Set the current layer to Wall, and proceed to add the stairs and exterior walls of the building, as shown in Figure 6.6. (Remember that you exported the stairs from the Lobby drawing in the last chapter. You can also use the Stair.dwg file from the companion CD.)

   Figure 6.6: The stairs and walls added to the restored First view

4. Use the View dialog box again to restore the view named Second. Then add the walls, as shown in Figure 6.7.

   Figure 6.7: Walls added to the restored Second view

5. Continue to the other views and add the rest of the exterior walls, as you have done with First and Second. Use the four panels in Figure 6.8 as a guide to completing the views.

   Figure 6.8: Walls, stairs, and doors added to the other views

   Tip	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. Choose View   Zoom   Extents, or type Z E .

2. Enter “View s at the command prompt or use the “V s shortcut. (Don't forget the minus sign in front of View or V. )

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 the Overall view at any time. (Choosing View   Zoom   All gives you an overall view too, but it might zoom out too far for some purposes, or it might not show what you consider an overall view.)

The Select File dialog box contains a Select Initial View check box. If you open an existing drawing with this option selected, you are 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 have saved views and you know the name of the view you want, using Select Initial View saves time when you're opening large files.

Understanding the Frozen Layer Option

As mentioned earlier, you might want to turn certain layers off altogether 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 dialog box 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 are not needed for reference or editing, you can reduce the time AutoCAD takes to perform regens. This can be helpful in very 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 invisible:

1. In the Layer Properties Manager dialog box, set the current layer to 0.

   Tip	You can freeze and thaw individual layers by clicking the Freeze/Thaw icon (which looks like a sun) in the layer list in the Properties toolbar.

2. Click the yellow lightbulb icon in the Plan1 layer listing to turn off that layer, and then click OK. Nothing happens to your drawing. Turning off the Plan1 layer, the layer on which the unit blocks were inserted, has no effect.

3. Now use the Layer Properties Manager dialog box to turn off all the layers.

4. Open the Layer Properties Manager dialog box again, and turn all of the layers back on.

5. Click the Plan1 layer's Freeze/Thaw icon. (Note that you cannot freeze the current layer.) The yellow sun icon changes to a gray snowflake , indicating that the layer is now frozen.

6. Click OK. Now the unit blocks disappear.

Even though none of the objects within 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.

You don't really need to have the Plan1 layer frozen. Do the following to turn it back on.

1. Issue the Regen command again and pay attention to the time it takes. The regen is faster this time.

2. Now, thaw layer Plan1 by opening the Layer Properties Manager dialog box and clicking the snowflake icon in the Plan1 layer listing.

3. Turn off the Ceiling layer. Exit the dialog box.

In this relatively small file, the differences between the regen times of the Off and Freeze states are insignificant. But in larger files, the difference can be quite significant. As your drawings become larger, try this exercise again to see how Off affects your regen speed compared with Freeze.

Making Good Use of Freeze and Off

The previous exercise showed the effect that freezing a layer has on blocks. When the layer of a block 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 are not frozen, the individual objects that are a part of a block are still affected by the status of the layer to which they are assigned.

You can take advantage of this feature by using layers to store parts of a drawing that you might want to plot separately. For example, three floors in your apartment building plan might contain the same information, with some specific variation on each floor. In this case, you can have one layer contain blocks of the objects common to all the floors. Another layer contains the blocks and objects specific to the first floor, and additional layers contain information specific to the second and third floors. When you want to view or plot one floor, you can freeze the layers associated with the other floors. With respect to Freeze/Thaw visibility, external referenced files inserted by using the Xref command also act like blocks. For example, you can Xref several drawings on different layers. Then, when you want to view a particular Xref drawing, you can freeze all the layers except the one containing that drawing.

In larger projects, you might not want to combine all your floors into one file, but instead combine different types of data such as electrical, mechanical, interior, site, and lease data. When you want to plot an interior plan, for example, you turn off or freeze layers associated with other disciplines. In fact, this is how the San Francisco Main Library project was organized. However, you can still use common data such as structural grids, columns , elevator core, and staircase drawings as part of all your floor plan files.

Using layers and blocks in these ways requires careful planning and record keeping. If used successfully, however, this technique can save substantial time when you're working with drawings that use repetitive objects or that require similar information that can be overlaid.

Taking Control of Regens

If you work with extremely large files and regen times become a problem, you can control regeneration by setting the Regenmode system variable to 0 (zero). You can also use the Regenauto command to accomplish the same thing, by typing Regenauto Off .

If you then issue a command that typically triggers a regen, AutoCAD will give the message Regen queued . For example, when you globally edit attributes, redefine blocks, thaw frozen layers, change the Ltscale setting, or, in some cases, change a text style, you will get the Regen queued message. You can "queue up" regens and then, at a time you choose, issue a regen to update all the changes at once by choosing View   Regen or by typing Re . This way, only one regen occurs instead of several over the course of an editing session.

By taking control of when regens occur, you can reduce the overall time you spend editing large files.