Many beginners do not completely understand the use of selections sets and their subtleties. Improving your ability to manipulate a selection set can help your CAD productivity, and is essential if you want be be able to confidently use the BLOCK and WBLOCK commands.

Creating and manipulating the selection set

Even though you may not be aware of it, every time you pick an enitit(ies) to move it, copy it or whatever, you automatically create a selection set. The entities can be selected in a number of different ways and once in the selection set can be further manipulated. You add, subtract to the selection set.

Let's imagine that you are viewing a drawing which consists of a collection of primitive elements such as lines, arcs, circles, points, text etc. 

If you want to erase, copy, or move any entity in the drawing, you pick it with the left button of your mouse or digitizer. When you 'pick' it, the entity is automatically highlighted (dotted) and is added to what is called a 'selection set'. 

If you look carefully in the Command area (use F2 if necessary to pop up the text window), AutoCAD/IntelliCAD reports back to you, "Entities in Set 1". 

If you had initially chosen to erase a line, and then realized that you now wanted to erase a nearby circle, you simply pick the circle, AutoCAD adds the circle to the selection set, reporting "Entities in set 2". 

Hitting the enter key will then execute the command, operating on the selection set, erasing both the line and the circle. By adding an item at the second pick, you are manipulating the selection set.

Click here to watch a movie describing selections sets.

Selection sets

Open the drawing called 'Primitives' in the Exercises folder.

See if you can use the ERASE command to add and subtract from a selection set.

Selecting items

When you choose a command that requires you to select entities (when you're deleting or changing entity properties, for example), you can use any of the following selection methods, which are displayed in a prompt box:

• Select all entities (Selects all entities in the current drawing).
• Add to set Adds one or more entities to the selection set.
• Subtract from set Removes one or more entities from the selection set.
• Previous selection Selects entities included in the previous selection set.
• Last entity in drawing Selects the entity most recently added to the drawing.
• Window-Inside Selects entities contained entirely within a rectangular selection window.
• Crossing window Selects entities contained within or crossing the boundary of a rectangular selection window.
• Outside window Selects entities falling completely outside a rectangular selection window.
• Window polygon Selects entities contained entirely within a polygon selection window.
• Crossing polygon Selects entities contained within or crossing the boundary of a polygon selection window.
• Outside polygon Selects entities falling completely outside a polygon selection window.
• Window circle Selects entities contained entirely within a circular selection window.
• Crossing circle Selects entities contained within or crossing the boundary of a circular selection window.
• Outside circle Selects entities falling completely outside a circular selection window.
• Point Selects any closed entities that surround the selected point.
• Fence Selects entities crossing a line or line segments.

movie and exercise showing different methods of selection.

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Creating selection set by properties

You can create a selection set by indicating the 'properties' of entities that you require.

For example if you wanted to change the radius of a group of circles, it is possible to use the properties option.

click here for movie showing changing diam of circles (done)

Changing methods of selection

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Entity-selection methods

movie showing selection by properties, primitives drawing needs some layering and maybe a block layers, linetypes, colours objects (blocks) circles of certain value, text certain height.

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In addition to these methods, you can select entities that match a particular set of properties—for example, all entities on a particular layer or drawn in a certain color.

move bit under to top

You can also use a few selection methods automatically, without displaying the prompt box. For example, you can simply click to select entities, or you can use a Window-Inside or Crossing Window by defining the opposite corners of a rectangular selection window. The direction in which you define the points of the rectangle (left-to-right or right-to-left) determines which type of window you create.

Shift and control keys

AutoCAD and IntelliCAD will allow the shift and control keys to be used with the pick button to good effect - adding and removing items from the selection set. Rather than describe it, simply try it for yourself. Note that the response is dependent on the AutoCAD settings (noun/verb settings). 

AutoLISP and selection sets

AutoLISP can be used to aid in the selection of entities.  A Lisp routine delivered with an early version of AutoCAD called ssx.lsp enables the selection of groups of entities such as text, blocks, etc.  These can even be selected on different layers.

The syntax to load ssx is given below;

(load "ssx")

More detail on how to use ssx can be found in the Lisp file itself.

This really reinforces that you need be very orgainised in your drafting.