The Quintessential Selection Set

31 Jul, 1998 By: Lynn Allen

For those of you who have written me expressing frustration that I've been focusing entirely on AutoCAD Release 14-I've heard your cries! You'll be able to relate to this column regardless of which release you have-as will the AutoCAD LT crowd. This month, we'll look closely at the many options that exist in selecting objects-something we do quite frequently in our daily AutoCAD routine.

Are you stuck in a Windowing rut? Do you find yourself using several windows to get the exact objects that you need? Have you ever wondered what the difference was between Last and Previous? Do you find yourself staring at the Select objects: prompt and thinking, "There must be other options?" If you answered yes to any of these questions, read on!

There are 17 different options for selecting objects (yes-seventeen!). That's a lot of options, and most of us only know about three or four of them. Back in the old days of AutoCAD, selecting objects was simple. The prompt read: Select objects, Window or Last: There were three, and only three, options. Over the years, Autodesk has tried to satisfy the users' wishes by adding new options. I'm sure you'll find most of these 17 different options to be useful, and I hope that they will encourage you to expand your selection set horizons. I've listed 16 of the many different options below-the 17th option is the simple pick to select an object. One by one, we'll walk through these different options: AUto, Add, ALL, Box, Crossing, Cpolygon, Fence, Group, Last, Multiple, Previous, Remove, Single, Undo, Window and Wpolygon.

I've listed them in the order found in the AutoCAD HELP function. Is it just me, or does someone need help with their alphabetizing? I did notice, however, that AutoCAD LT had them listed in the proper order. Enough of the banter; on to the good stuff!

I predict that most of you use selecting objects one at a time and automatic windowing 90 percent of the time. Automatic windowing refers to the automatic standard and crossing windows that appear when you select a point on the screen where no object resides. Moving the window from left to right creates the standard window, and moving it from right to left yields a crossing window. The standard window is solid; the crossing window is dashed. The standard window selects only those objects that are found completely within the selection window. A crossing window selects all objects that are completely within the selection window, as well as those that cross the window, as shown in Figure 1. If one quarter of a line was within a crossing window with three quarters hanging out, the line would still be selected.

Selecting objects one at a time is easy. Place the pickbox on top of the desired object and pick. The pickbox can be made larger or smaller by using the PICKBOX command. The pickbox is measured in pixels. For those of you who are bad shots or lose to your kids at Nintendo, you might find it useful to enlarge the pickbox. Making it smaller can come in handy, as well, when you're trying to squeeze into smaller areas.

Note: If the system variable PICKAUTO is not set to ON, you will not get the automatic windowing.

AUto and BOX go hand in hand. They've traditionally been used in menus to force the automatic window we just covered. If the user accidentally turned PICKAUTO to OFF, the menu selection would still force automatic windowing.

AUto forces the automatic windowing discussed above. If the user picks in a location where no object resides, it goes into the Window/Crossing window mode. If the user picks in a location where there is an object then that object is selected and no window appears.

BOX forces an automatic window only, even if the user selected on top of an existing object.

Add and Remove also work together. They're used to add and subtract objects from an existing selection set of objects. Let's say you want to Move all of the objects in one section save for a couple of objects right in the center. Do you painfully select the desired objects by using multiple windows? No! It would be so much faster to select all of the objects in the section and then remove one or two objects from the final selection set. The Remove option is used for this exact reason. When selecting the Remove option, you'll find the familiar Select objects: prompt is changed to Remove objects. Should you choose to go back to the Select objects: prompt, you'll need to use the Add option (just type A for short). As you are flipping back and forth between the add and remove modes, note that objects will verify their selection or de-selection on the screen.

Note: If someone has turned off the pickadd variable, you will only be allowed one chance to select objects. Due to this, you may see an occasional Add option added to menus to ensure the user has the opportunity to select more then once. It's doubtful that you (or anyone) would intentionally set this value to off.

A few releases ago, Autodesk added the Shift to remove feature to AutoCAD. This is much easier to use than the Remove option because there's no need to key in R. Simply hold down [Shift] to remove objects from the selection set. While holding down [Shift], you can also use automatic windowing. In this situation, there is no need for the Add option. This is a great feature that's highly underutilized.

All is used to select every darn object in your drawing. The only objects safe from this option are those on frozen or locked layers. Save this option for really bad drawing days!

Note: The AutoCAD HELP function is remiss in not mentioning locked layers, however, the LT help function mentions it.

Crossing Polygon and Window Polygon are two great underused selection secrets! The objects we want to select don't always lie conveniently within a rectangular area. Hence, rectangular windows don't always do the trick. The CP and WP options allow you to create a polygonal area with as many sides and whatever shape you'd like. Rather than creating several windows to get the desired objects, try using these two options. CP selects all the objects within or crossing the polygonal area, WP selects only those objects that fall completely within the polygon.

There is one rule that both CP and WP must follow-the Polygon cannot cross or touch itself. AutoCAD continually sketches in the last segment to ensure a closed polygon. You'll notice an Undo option should you accidentally select an incorrect location for a polygon vertex.

Use the Fence option when it's easiest to draw a series of connected line segments through the desired objects. Fences don't need to close, and they can cross themselves. You'll also find the Undo option here in the Fence selection should you pick an incorrect point.

Have you ever wanted to save a group of objects for future editing purposes? The GROUP command lets you do exactly that. You can name a group of objects to be used later as a selection set. You can also use this same group over and over again. I don't have space to address this can of worms in this column, but take a look at the GROUP command if this is one of your design needs. Should you create a GROUP, you can call to that group by using the G option. For example:

Select objects: g

Enter group name: desks

Note: The Group command and option are not available for LT users.

Last and Previous are often mistaken for each other. Last is used to select the last object created in the database. Previous is used to select the previous selection set. For example, let's say you want to move and array a group of objects. Select the group of objects once for the Move command and use the Previous Selection option when you enter the Array command.

I believe the Multiple option remains in AutoCAD primarily due to legacy. This option permits the individual selection of many objects (by picking) without highlighting them. This is intended to speed up the selection process (should you be using a 286?). You pick and pick and pick and hope you picked the correct objects. If you pick at an intersection twice, both objects will be selected (though this doesn't always work). When you think you've selected all of the objects, hit [Enter] and the objects become highlighted. Years ago, on very slow machines, this was occasionally used, but I don't hear of it being used today (please enlighten me if I'm wrong!).

SIngle is used primarily in menus. When entered, the user gets only one chance to select objects before the command progresses to the next step. I can think of no reason that you'd use this in your daily drawing routine.

Undo is an obviously popular option. Should you select the wrong objects, there's no need to cancel the operation and start over; just use the Undo option to deselect the last object(s) selected. Take the lazy route and don't do any more work than absolutely necessary!

One last point of interest in selecting objects is Object Cycling. Have you ever tried to pick an object in a crowd but found that AutoCAD keeps grabbing the wrong one? Object Cycling to the rescue! You'll find that if you hold down [Ctrl] while picking, AutoCAD will cycle through all the objects that fall under the pickbox as you continue to pick. When the correct object is highlighted, simply hit [Enter]. You don't need to continue to hold down [Ctrl] after the first pick. Try it, it's a great addition to your newfound selection set knowledge.

Are you open to trying some of the other selection set options? You'll have to force yourself to get out of that automatic windowing habit (no CAD patch?) but I'm sure you'll find the advantages worthwhile. Until next month...

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