What You See is What You Get

28 Feb, 1998 By: Lynn Allen

Any CAD user can tell you that controlling the display of your drawing is incredibly important to the design process. AutoCAD provides many different means of viewing your drawing, some more efficient than others. This month, we'll review the most commonly used display commands and take a tour through the new additions to AutoCAD R14.

For those of you who survived the R13c releases (which one comedic user penned "c what we fixed now"), you found c4 filled with some refreshing surprises. One such surprise was the real-time PAN and ZOOM commands. We have the magnificent HEIDI driver to thank for this new capability. Though the Rtpan and Rtzoom toolbars were tedious to load into our drawing, (and once loaded, difficult to keep), they proved to be awesome tools for moving around in a drawing. R14 moved them to the standard toolbar (prime real estate) and even made them the default option in the ZOOM command (for you command-line buffs). Throw in the new right-click menu and you've really streamlined your productivity! Let's take a look. Open up a drawing and we can zoom together. (Sounds like a pickup line!)

The RTPAN and RTZOOM commands are easily accessed by selecting the toolbar buttons. You can also find them in the View pulldown menu under Zoom.

Selecting the Rtzoom tool will display a magnifying glass in your drawing area. Notice the + sign in the upper right corner and the - sign in the lower left corner of the icon. If you hold your Pick button down while moving the cursor up, you'll find that you're increasing the magnification of your display (or ZOOMing IN). Similarly, if you hold your Pick button down while moving the cursor towards the bottom of the display, you'll find that you're decreasing the magnification of your display (or ZOOMing out). To continue to zoom in after moving all the way to the top of the drawing area, pick the input device up, place it at the bottom of your display and continue as before. Continue this procedure until you've zoomed in far enough (or until you've burned off enough calories). If you zoom in too far, you'll find that the + sign disappears-this indicates that you've reached the maximum zoom depth stored in memory. Consequently, if you zoom out too far, you'll find that the - sign disappears, thus indicating that you've reached the minimum zoom depth stored in memory. You have to do some serious zooming before you encounter either of these two situations. You'll also notice that RTZOOM zooms in on the center of the display.

Let's take a look at what displays at the command line prompt when you're using the RTZOOM command.

Command: RTZOOM.

Press [Esc] or [Enter] to exit or right-click to activate pop-up menu.

Either [Esc] or [Enter] will kick you out of the command and leave you at your current display. The pop-up menu is a nice R14 addition that really makes RTZOOM usable. You seldom want to zoom in on the center of the display, so it's important that you can easily switch over to Rtpan mode. Do a right-click while in RTZOOM, and you'll see the cursor menu, as shown in Figure 2.

Selecting Pan will put you in the RTPAN command, and an icon of a hand will display on your screen. Holding down the Pick button while moving your cursor around on the screen will dynamically move the display around without changing the magnification. If you need to change the magnification, it's easy-right-click and return to RTZOOM. You'll notice that the old PAN command has been replaced with RTPAN. I was surprised when I keyed in the alias of P for PAN and was in the RTPAN command. Take a look at the other options in the right-click menu:

Exit: Guess what that does!
Zoom Window: This option puts you into the popular window option of the ZOOM command.
Zoom Previous: This option returns you to the last display you had on the screen before entering the RTPAN or RTZOOM command.
Zoom Extents: This option will zoom you out so that all of your objects are displayed on the screen. Before R14, this action required a regeneration of the drawing (which could be quite painful in large drawings). Now, you'll find the Zoom Extents to be as fast as a redraw (Hoorah!). You might also notice that it zooms just a tad further out than before, so the objects aren't actually touching the edge of the display (thus making it much easier to see them).

You'll also notice that RTZOOM is the newest of an onslaught of defaults in the ever popular ZOOM command. So how many different defaults can a command have? The ZOOM command takes the cake with three different defaults.

Command: ZOOM


If you pick from the screen, the ZOOM command will assume you are choosing a window (no W required). If you key in a number, AutoCAD will assume you're indicating a scale factor (x or xp) and if you hit an [Enter], it will launch you into Realtime Zoom (RTZOOM). While we're here, let's run through a quick summary of the other options for those new to AutoCAD or AutoCAD LT.

What's the difference between Zooming All and Zooming Extents? Zoom Extents will zoom out until all of the objects on the screen are displayed. If you have a small circle on the screen and you perform a Zoom Extents, AutoCAD will zoom in on the circle. AutoCAD won't care what your limits are set to in calculating the display of a Zoom Extents. Zoom All, on the other hand, will zoom out to the extents of the objects or to the limits-whichever is larger. As a reminder, the limits is the area of your drawing that is covered by the grid. The Help file indicates that Zoom All always performs a regeneration, but I no longer find that to be the case in R14 (which is a good thing!). Of course, it says the same about Zoom Extents. The Help file also indicates that you cannot execute either Zoom All or Zoom Extents transparently (from within another command), and that's not true either. I had no problem performing either transparently. To further confuse you, you will also find that when working in 3D, a Zoom All actually zooms to the extents of the drawing.

Zoom Center will zoom in relative to a center point that you select. You will be asked to supply a magnification factor or a height. A smaller value for the height increases the magnification, and a larger value decreases the magnification. This usually requires too much work (and thought) for me, so I'm apt to stick to zooming via a window.

I actually marvel that ZOOM DYNAMIC still exists now that RTZOOM has been added to the command palette. When ZOOM DYNAMIC first came out, it was such an exciting addition to the product. I don't know anyone who still uses it ('fess up if you do!). ZOOM DYNAMIC uses a view window similar to that seen in the Aerial Viewer to determine the final display. The Pick button is used to control the size and the position of the view window. The view window is moved to the proper location, and an [Enter] executes the zoom (though you'd think a final pick would do so). I could zoom many windows in the amount of time it takes to use ZOOM DYNAMIC. Previously, we would use ZOOM DYNAMIC to avoid those painful, time-consuming regenerations, but that's not really an issue anymore.

ZOOM PREVIOUS was mentioned earlier. You can go back up to 10 previous zooms (should you be able to remember what was on the screen 10 zooms ago!).

ZOOM SCALE has three different options, depending on the syntax you use. If you key in a straight value, such as 2 or 4, AutoCAD will use this scale to zoom relative to the drawing limits. For example, a value of 1 would zoom to the limits of the drawing. A value of 2 would change the magnification of the zoom lens you were looking through to twice the value. A value less then 1 actually pulls away from the drawing. AutoCAD uses the center of the drawing limits as the center of the final display.

You can also add an X to the end of the specified value, which will cause AutoCAD to zoom in relative to the current display rather than the entire drawing. For example, Zoom 2X will zoom in two times the current display and Zoom 4X will zoom in four times. It's not uncommon to see an AutoCAD pro using a zoom of .8x to pull the current display out just a tad. This practice was especially popular when Zoom Extents zoomed out to the very edge of the drawing display (before R14).


Table 1.
Zoom XP Scale Factors

1" = 1 foot 1/12XP

12" = 1 foot 1/24XP

14" = 1 foot 1/48XP

1=100 1/100XP

2=1 2XP

4=1 4XP

And then there's ZOOM XP. Those of you proficient in Paper Space know that this option is key to your Paper Space dimensioning success. Rather than launch into a painful dissertation on Paper Space, I'll attempt to summarize. One of the advantages of using Paper Space is the ability to have more than one scale factor per drawing. ZOOM XP is used to set up these scale factors within your viewports. Table 1 indicates some of the XP settings per scale factor.

Essentially, you'll be taking the value shown on the left (in units) in Table 1 and dividing it by the value on the right. For example: 1" = 1 foot is the same as 1 = 12; 1 divided by 12 equals 1/12, hence 1/12XP. You can also use the decimal equivalent.

If you set up your viewport scale factors using ZOOM XP and set the dimscale factor to 0 (or select the Scale to Paper Space option in the Dimension Style dialog box), your dimensions will display at the size you've specified. AutoCAD looks at the XP factor per viewport to ensure that all your dimensions will display at the same size.

Back to Zooming
You astute AutoCAD wizards might have noticed that two of the Zoom options are no longer listed in AutoCAD R14: Left and Vmax. Both of these two options are accepted if you key them in, but I wouldn't count on them being supported in future releases.

Zooming is basic to designing with AutoCAD; hence, it's very important that you thoroughly understand it. So many different methods of controlling the display in your drawings exist-be sure you're using the best one!

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