Object Selection


Introduction
 Before you start to use the AutoCAD Modify commands, you need to know something about selecting objects. All of the Modify commands require that you make one or more object selections. AutoCAD has a whole range of tools which are designed to help you select just the objects you need. This tutorial is designed to demonstrate the use of many of the selection options. As with so many aspects of AutoCAD, developing a good working knowledge of these options can drastically improve your drawing speed and efficiency.

Selecting Objects by Picking
 Perhaps the most obvious way to select an object in AutoCAD is simply to pick it. Those of you who have used other graphics based utilities will be familiar with this concept. Generally all you have to do is place your cursor over an object, click the mouse button and the object will be selected. In this respect AutoCAD is no different from any other graphics utility.

When you start a Modify command such as ERASE, two things happen. First, the cursor changes from the usual crosshairs to the pickbox and second, you will the the "Select objects" prompt on the command line. Both of these cues are to let you know that AutoCAD is expecting you to select one or more objects.

Select objects:

To select an object, place the pickbox over a part of the object and left-click the mouse. When the object has been picked it is highlighted in a dashed line to show that it is part of the current selection and the command line reports "1 found". You will now see the "Select objects" prompt on the command line again. At this point you can continue adding more objects to the current selection by picking them or you can press Return or the Space Bar to complete the selection.

The Cross-hairs The Pickbox A Highlighted Object
The Crosshairs The Pickbox Highlighted Object
When you pick one or more objects in response to the "Select objects" prompt, you are effectively creating a selection set. Selection sets are an important concept in AutoCAD because they can be used to great effect, especially when drawings become large or complicated.

An Example
 Follow the example below to get an idea how a selection set can be created by picking objects.

Draw Two Circles
Draw two circles using the CIRCLE command, DrawCircle from the pull-down menu or Circle from the Draw toolbar. The size and position of the circles does not matter.

Command: CIRCLE
3P/2P/TTR/<Center point>: (pick a point in the middle of the drawing window)
Diameter/<Radius>: (pick another point to define the circle circumference)
Command: CIRCLE
3P/2P/TTR/<Center point>: (pick the center point of the second circle)
Diameter/<Radius>: (pick another point to define the circle circumference)

Erase the Two Circles
Erase the two circles using the ERASE command, ModifyErase from the pull-down or Erase from the Modify toolbar.

Command: ERASE
Select objects: (place the pickbox over a circle circumference and left-click)
1 found
Select objects: (place the pickbox over the second circle circumference and left-click)
1 found
Select objects: (press Return to complete the selection and erase the objects)

Creating selection sets by picking objects can become quite tedious if you want to select a large number of objects. Just imagine having to pick a hundred or more objects in a large drawing! Fortunately AutoCAD provides a number of selection options which can help you select objects more efficiently.

Window Selection
 The Window option is invoked by typing W in response to the "Select objects" prompt. Window allows you to define a rectangle using two points in exactly the same way as the RECTANGLE command. Once the window is defined, all objects which lie entirely within the window will be selected.

Window selection Objects within Window
The Window selection box is shown
as a rectangle with a solid line		 Only objects entirely within the
window will be selected
Command Sequence
 Command: (start one of the Modify commands such as ERASE)
Select objects: W
First corner: (pick first corner)
Other corner: (pick second corner)
Select objects: (at this point you can either select more objects or Return to complete the
selection set and continue with the current command.)

Crossing Window Selection
 The Crossing Window option is invoked by typing C at the "Select objects" prompt and is a variation of the Window command. The command sequence is exactly the same but objects are selected which lie entirely within the window and those which cross the window border.
Crossing selection Objects crossing Window
The Crossing selection box is shown
as a rectangle with a broken line		 Objects within and crossing the
window will be selected


Implied Windowing
 Although you can explicitly invoke the Window and Crossing Window selection boxes by entering W or C at the keyboard when prompted to "Select objects", in practice this is rarely done. Both of these selection options are so commonly used that AutoCAD provides a method of implied windowing so that you don't have to use the keyboard at all. You can test this out without using any command. If you pick a point in space on the graphic window, you will notice that AutoCAD automatically assumes that you want to define a selection window and uses the pick point as the first point of that window. If you move the cursor to the right of the pick point you will get a Window selection box (solid line). If you move the cursor th the left you will get a Crossing Window selection box (broken line). With a little bit of practice the use of implied windowing can make the whole drawing process very efficient and you will rarely find yourself having to explicitly invoke the window selection options from the keyboard.

The Undo Option
 It often happens that you inadvertently add objects which you don't want to a selection set during its compilation. When this occurs in the middle of a complicated selection it can be pretty annoying. Fortunately AutoCAD allows you to undo the last selection made during the compilation of a selection set. All you need do is enter U at the next "Select objects" prompt to remove the objects previously added.

Selecting All Objects
 The All option is invoked by typing ALL at the "Select objects" prompt. You can use this option to select all the objects in the current drawing, no picking is required. Objects on Locked or Frozen layers are not selected but objects on layers which are simply turned off are selected.

Fence Selection
Fence in action The Fence option allows you to draw a multi-segment line, like a Polyline. All objects which cross the fence will be selected. The Fence option is invoked by typing F at the "Select objects" prompt.

Command: (start one of the Modify commands such as ERASE)
Command Sequence
Select objects: F
First fence point: (pick first point)
Undo/<Endpoint of line>: (pick second point)
Undo/<Endpoint of line>: (pick another point or Return to end fence selection)
Select objects: (Return to complete the selection set or add more objects)

Window Polygon Selection
Window Polygon in action The Window Polygon option, invoked by typing WP is similar to the Window option except that you can define an irregular polygon shape within which objects will be selected. As with the Window option, only objects which fall entirely within the polygon will be selected.

Command Sequence
 Command: (start one of the Modify commands)
Select objects: WP
First polygon point: (pick first point)
Undo/<Endpoint of line>: (pick second point)
Undo/<Endpoint of line>: (pick third point)
Undo/<Endpoint of line>: (pick another point or Return to end polygon selection)
Select objects: (Return to complete the selection set or add more objects)

A polygon is formed by picking at least three points.

Crossing Polygon Selection
 The Crossing Polygon option can be used in exactly the same way as the Window Polygon option but it has the same selection criteria as the Crossing Window option, i.e. objects will be selected if they fall entirely within or touch the polygon boundary. This option is invoked by typing CP at the "Select objects" prompt.

Note:
Lines, polygons and windows drawn using the selection options do not exist as drawing objects. Once the selection has been made they disappear.

Using a Previous Selection
 AutoCAD always remembers the last selection set you defined. This is very useful because you may need to make a number of changes using different commands to the same group of objects. In order to re-select the last selection set you can use the Previous option. The previous option is invoked by typing P at the "Select objects" prompt.

Selecting the Last Object
 You can select the last object created by entering L at the "Select objects" prompt.

Object Cycling
 When drawings become complicated it is sometimes difficult to select the particular object you want because it is either very close to or overlies another object. In such a case it may happen that the other object is selected and not the one you want. Object cycling is designed to overcome this problem. If you make a pick whilst holding the Control (Ctrl) key down, AutoCAD will respond with "<Cycle on>". If you continue to pick, each object near the pick point is highlighted in rotation. Just keep picking until the object you want is highlighted, then right-click or Return, AutoCAD responds "<Cycle off>", the required object is added to the selection set and you can continue to select more objects as normal.

Adding and Removing Objects
 AutoCAD provides two methods for adding and removing objects to and from a selection set. As you know, objects can be added to a selection set simply by picking them or by using one of the methods outlined above. You can remove selected objects from a selection set just as easily by shift picking. If you hold the Shift key down on the keyboard while picking a selected object, that object will be deselected (removed from the current selection set). You can tell when a selected object has been deselected because it is no longer highlighted. You can remove more than one object at a time by holding down the Shift key while using implied windowing. However, none of the other selection options which require keyboard input will work using the shift pick method.

If you need to remove a more complex selection from the current selection set you should use the Remove option to switch to Remove mode. If you enter R at the "Select objects" prompt, AutoCAD will respond:

Remove objects:

Objects now picked or selected using any of the above methods will be removed from the current selection set. When you have finished removing objects, you can return to Add mode by entering A at the "Remove objects" prompt.

You can use any combination of picking, selection options and add/remove modes to define your selection set. Once you are happy that you have selected all the objects you need, just hit Return to complete the selection process and to continue with the current command.

Object Selection Filters
 It may sometimes happen that you need to create a selection set of objects based upon one or more of their properties. For example, you may want to select all objects on a particular layer or more particularly, you may even want to select all circles on that layer. This type of selection is not easy with the options discussed above. Fortunately AutoCAD provides a method to filter objects based upon selection criteria.
Toolbar not available
Pull-down not available
Keyboard FILTER or FI
Object Selection Filters Dialogue Box

An AutoCAD drawing is simply a database of objects and their properties. Using the Filter command you can define a query just like you would in a database. If you look at the Object Selection Filters dialogue box, shown above, you will see that a filter has been defined which will select all circles on the CONSTRUCT layer.

To create a filter, click the arrow on the drop-down list in the Select Filter area and select the object type or property you would like to add to the filter list. Click on the "Add to List" button. You can add as many object types or properties to the list as you like. Having defined a filter list you can either use it as a one-off or you can save it as a named filter by typing a name in the Save As edit box and then clicking the "Save As" button. Your named filter will then be added to the Named Filters drop-down list and you can use it again at any time.

Although you can create filters using the Filter command from the command prompt, you will mostly want to use it during the course of a selection operation. Fortunately, the Filter command can be used transparently. This means that it can be used whilst another command is still running. To get an idea how this might work, follow the example below.

Create a Drawing

  1. Start a new drawing, click on New and select "Start from Scratch" from the Create New Drawing dialogue box.

  2. Use the Layer command, Layers from the toolbar or FormatLayer… from the pull-down menu to create two new layers called "CONSTRUCT" and "BOUNDARY". Set the CONSTRUCT layer colour to Green and the BOUNDARY layer colour to Red. Set the current layer to "CONSTRUCT".

    Note: If you need more information about layers, see the "Object Properties" tutorial.

  3. Draw a selection of objects, lines, polylines, ellipses etc. including several circles.

  4. Set the current layer to BOUNDARY using the Object Properties toolbar.

  5. Draw some more circles.

  6. Now you are going to erase just the circles on the CONSTRUCT layer, so start the ERASE command, Erase" from the Modify toolbar or ModifyErase from the pull-down menu.

Compile the Filter
  1. At the "Select objects" prompt enter 'filter. The apostrophe is very important, it tells AutoCAD that you want to use a command transparently.

    Select Layer(s) Dialogue Box

  2. When the Object Selection Filter dialogue box appears, select "Layer" from the drop-down list. The list is arranged alphabetically so you will need to scroll down the list to find it. When you have selected "Layer", click on the "Select…" button. The Select Layer(s) dialogue box appears, select "CONSTRUCT" from the list and click the "OK" button. You are now returned to the Object Selection Filter dialogue box, click the "Add to List" button, your layer selection is added to the list which now displays "Layer = CONSTRUCT".

  3. Next, select Circle from the drop-down list and click the "Add to List" button. "Object = Circle" is added to the list below the Layer entry. You have now completed the filter list.

Apply the Filter
  1. Click on the Apply button. The dialogue box disappears and you are returned to the "Select objects" prompt. The principle behind the filter list you have just compiled is that when applied to a selection, all objects which do not match the listed criteria will be filtered out. The simplest way to apply this filter to the whole drawing is to use the All selection option. Enter all at the prompt. All objects are selected but the filter ensures that all objects except the circles on the CONSTRUCT layer are filtered out.All the circles on the CONSTRUCT layer are highlighted to indicate that they are selected. and you are returned to the "Select objects" prompt.

  2. Enter Return at the prompt, AutoCAD responds:

    Exiting filtered selection.

    You now see the "Select objects" prompt again because you can add objects to the selection set without them being filtered. Enter Return again to complete the command. The green circles are erased, leaving all other objects unaltered.

This whole process may seem very long-winded but when you have to make this type of selection on a complex drawing you will thank your lucky stars that the Filter command exists.

Object Selection Settings
 Object Selection Settings Dialogue Box
Toolbar not available
Pull-down ToolsSelection…
Keyboard DDSELECT
The Object Selection Settings dialogue box (shown on the right) can be used to control many of the settings which have been discussed above and some which have not. In general it is advisable not to change any of the default settings unless you have good reason to do so.

Noun/Verb Selection allows you to select objects either before or after starting a command when it is checked.
Use Shift to Add, does just that when checked. The default is to remove objects when shift picking, as described above.
Press and Drag enables selection windows to be defined by picking and then dragging the mouse when checked. The default method for defining a selection window is to use two pick points.
Implied Windowing enables this type of selection when checked. See "Implied Windowing" above for details.
Object Grouping enables a group of objects to be selected by picking only one of the objects in the group when it is checked.
Associative Hatch causes a hatch boundary to be selected along with the hatch when it is checked.

You can use the "Default" button to reset these options back to their default settings at any time.

Pickbox Size
 You can also use the Object Selection Settings dialogue box to change the pickbox size. Use the slider bar to increase or decrease the size. The larger the size of the pickbox the wider the area which AutoCAD looks for objects. Generally the pickbox is better set to a smaller size to make picking more accurate. The default setting works very well and it is unlikely that you will need to change it.

Object Sort Method
 Object Sort Method Dialogue Box The "Object Sort Method…" button brings up the Object Sort Method dialogue box (shown on the right). This dialogue box enables you to optimise the way objects are selected with respect to different operations. Objects will be added to selection sets in the order in which they appear in the drawing database for each method that is checked. Although the "Plotting" and "PostScript Output" methods are the only ones set by default, it is often advantageous also to check the "Object Selection" method so that more recent objects are selected before older ones for general drafting. Since processing time is increased for each additional method selected, it would also be advantageous to uncheck the "PostScript Output" method unless you intend to use PostScript output, of course.

Tips & TricksHot Tips

  • When you are picking objects in a complex drawing, use the ZOOM command transparently to make object selection easier. All Zoom options selected from the toolbars are automatically transparent but if you invoke the command from the keyboard you will need to enter 'zoom.