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By now you should be familiar with the Pan and Zoom functions in . There are many other tools at your disposalthat can 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 Redraw

AutoCAD uses two methods for refreshing your 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. AutoCAD stores drawing data in two ways; one is like a database of highly accurate coordinate information and object properties. This is the core information you supply as you draw and edit your drawing. The other way is a less accurate, simplified database of just the display information. 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, you are telling AutoCAD to reread this virtual display data and display that information in the drawing area. A regen, on the other hand, causes AutoCAD to rebuild the virtual display based on information from the core drawing database. As you edit , you may find that some of the lines in the display disappear or otherwise appear corrupted. Redraw will usually restore such distortions in the display. In earlier versions of AutoCAD, the Blipmode 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 changes occur to settings and options that have a global effect on a drawing, such as a line-type scale change, layer color change, or text style changes (you’ll learn more about text styles in Chapter 8). In fact, in many situations, regens an’ performed automatically when
such changes occur. You usually don’t have to issue the Regen command on your own, except under certain situations.

Regens can also occur when you select a view of a drawuu; that 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 that is outside that  display.

In past versions of AutoCAD, regens were to be avoided at all cost, 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 in multimegabyte files, and if you are using an older Pentium-based computer, regens can still be a major headache. For these reasons,

it pays to urrderstand the finer points of controlling regens.
In this section, you will discover how to manage regens, thus reducing their impact on complex drawing. You can control how regens impact 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

This chapter will explore these methods in the upcoming sections

Exploring Other 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 of the virtual display’s area. If you use Pan Realtime and Zoom Realtime, you are automatically kept safely within the bounds 6£ the display list. In this section, you’ll be introduced to other tools that will help keep you within those boundaries.

Controlling Display Smoothness

The virtual display can be turned on or off using the Viewres command. Viewres setting is on by default, and for the most part, should remain on. You can turn it off by typing Viewres.J No.J at the command prompt. However, I don;t recommend this. With Vicwres ofi, a  Pan or Zoom.

The Viewres command also controls the smoothness of line types, arcs, and circles when they appear in an enlarged view. With the display list active, line types sometimes appear as continuous, even when they are supposed to be dotted or dashed. You may have noticed in previous chapters that on-screen arcs appear to be se&- mented 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 noncontii .ous line types, such as dashes or center lines, to appear as continuous

Another way to accelerate screen redraw is to keep your drawing limits to a minimum area. If the limits are set unnecessarily high, AutoCAD may 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 that represent very large areas. It’s called the Aerial view.

1. Click View >- Aerial View on the menu bar. The Aerial View window appears, as shown in Figure 6.4.
2. Click the Aerial View window. As you move your mouse, notice what happens in the AutoCAD window. Your view pans, following your motion in the Aerial View window. Abold 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 ana 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 th••rectangle representing your AutoCAD view is about half the size of the overall view of the plan, then right-click: Your AutoCAD view becomes fixed. Also notice that the magnification icen in the Aerial View toolbar becomes available.
As you can see from this exercise, yeu can cyclethreugh the Pan an« Zesm feature of the Aerial view by clicking the mouse. IT you simply want t. pan the view, you can right-click in step 2 of the last exercise to fix your view in place. Or you can rapidly alternate between the Pan ~El Zoom modes Ity clicking the m use until you’ve reached. the locati n and view size you want. The  rectangle shows you exactly where y u are in the overall drawing at any ,iven time. This feature is especially useful in derawings f large areas that may take several pans to. cross,

The Aerial View window is a ,at t 1when you are werking on a crawine that requires a lot of magnification in yeur zoomed-in views. It is also helpful when you need to maintain an overall view ef a drawing as YDU w rk n closer detaiL may n t find it very helpful on drawings that don’t require lots of magnification, like the athroom 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 Dol.! rectangle in the Aerial view.

View >- Zoom Out Zooms out of magnified view on tire view in the Aerial view.

View >- Displays an overall view Qf your drawing in the Aerial View windew, GI~)Palis like a View >- Zeem >- Extents .p •• n for the Aerialview.

Options >- Auto Viewport Controls whether a selected viewport is aut. matically displayed in the Aerial View win. ow. When checked, this option will cause the Aerial View window to automatically display the contents of a viewport when it becomes active, (See Chapters 12 and 16 fer more .n viewports.)

Options >- Dynunic Uptlate ‘Controls hew AutoCAD upaates the Aerial . View win.ow. When this settinc is on,AutoCAD updates the Aerial view’ in real tiJne as chances in the firawinc eccur, When it is off, changes in the cirawinc will not appearin the Aerial view until you click the Aerial View win

Options >- ltealtiJne “‘· Controls whether the AuteCA’D .isplay is
up.ate. in real time-as you :ZMm an« pan in the Aerial View window.

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