Autocad Tutorial

Object Selection Modes

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Toolbar	not available
Pull-down	ToolsOptions…
Keyboard	DDSELECT

The Selection tab of the Options dialogue box (extract shown on the right) can be used to control many of the settings that have been discussed above and some that 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.

Pickbox Size

You can also use the Selection tab of the Options 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 in 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 Sorting Methods

Object sorting methods are controlled from the User Preferences tab on the Options dialogue box, ToolsOptions… from the pull-down menu. The object Sorting Methods section of the dialogue is shown on the right. These options enable 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.

Create a Drawing

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

Draw a selection of objects, lines, polylines, ellipses etc. including several circles.
Set the current layer to "Boundary" using the Object Properties toolbar.
Draw some more circles.
Now you are going to erase just the circles on the Construct layer, so start the ERASE command, from the Modify toolbar or ModifyErase from the pull-down menu.

Compile the Filter

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

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.
Enter 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 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. However, if your selection requirements are more reasonable, try the Quick Select command as an

Object Selection Filters

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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 relatively easy with the Quick Select command discussed above. However, what if you wanted to select all green circles and lines on a particular layer? As good as Quick Select is, it cannot create selections from so many parameters. Fortunately AutoCAD provides a method to filter objects based upon a wide range of selection criteria.

Toolbar	not available
Pull-down	not available
Keyboard	FILTER or FI

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 that 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.

Quick Select

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The selection tools described in the Object Selection tutorial are fine if you only need to pick a few objects at a time or if you can easily see the objects you want to select. Sometimes though, your selection requirements may not be quite so simple. AutoCAD enables you to create selection sets by building database style queries that can make complex selections really quick and accurate. This tutorial describes the use of AutoCAD's advanced selection tools and how the selection options can be configured for better selection efficiency.

Quick Select

Toolbar	not available
Pull-down	ToolsQuick Select…
Keyboard	QSELECT

Quick Select made it's debut in AutoCAD 2000 and is designed to help users make complex selections quickly. It is also designed to be a simplified version of the Filter command, detailed below. Quick Select allows you to make selections based upon object properties. Say, for example, that you needed to select all circles on a layer called Water. Quick Select can help you do this. If you look at the dialogue box below, you will see that there are a number of parameters to set. To select all circles on the Water layer, you would make the settings shown in the dialogue box.

Let's have a closer look at the selection parameters in the Quick Select dialogue box. As with all dialogue boxes, it is important to move methodically through the various parameters. It is even more important in this case because the choices you make at the beginning of the process will affect the options available to you later. Start at the top of the dialogue with "Apply to" and work your way down.

The "Apply to" parameter can be used to cause the selection to be made from the entire drawing or from a selected part of the drawing. Use the Select objects button to create a selection set from which your more detailed selection will be made.
The "Object type" parameter allows you to select objects such as circles, lines etc. The drop-down list contains an inventory of all the different object types in the current drawing. If your selection is to be made from more that one object type, select "Multiple". Note that this parameter only allows you to select one object type or all objects. This is one limitation of Quick Select, although you can append selections to create compound selection sets, see below. However, if you want to make complex selections based upon multiple selection criteria, you may be better of using the more advanced features of the Filter command described below.
The "Properties" parameter allows you to specify which paricular property of an object type to apply to the selection. For example, circle properties include radius, diameter and circumference in addition to the standard object properties like layer and colour. So you could select all circles with with a particular radius or all circles on a particular layer.
The "Operator" parameter determines how the value is applied to the selection. For example, using the equals option with a circle radius and a value set to 24 would mean all circles with a radius of 24 are selected. However, other options available for the operator parameter allow you to select all circles of radius less that 24 or greater than 24 or even all circles except those with a radius of 24. Pretty amazing huh?
The "Value" parameter is used to specify the value of the property you have already chosen. For example, if you had specified Circle and Radius as your object type and property, you might enter "24" as a value. All circles with a radius of 24 would be selected. Or if you had specified Circle and Layer as your object type and property, you could select a layer name such as "Water". In this case, all circles on the layer called Water would be selected.

Finally, using the "How to apply" box, you have the option to have the selected objects either included or excluded from the new selection set. In addition, you can also have this selection appended to the current selection set. The "Append to current selection set" option is particularly useful because it means that you can use Quick Select repeatedly to build up compound selections. For example, you could use Quick Select to select all blue circles and then use it again to select all blue lines. Appending the blue lines selection to the blue circles selection would mean that you end up with a selection of all blue lines and circles.

As you can see, this is a very powerful tool and takes a little time to get used to. However, it is well worth making the effort as it can drastically improve your drawing efficiency. For your convenience, Quick Select is also available from the right-click context menu.

Modifying Object: The Explode Command

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Toolbar	Modify
Pull-down	ModifyExplode
Keyboard	EXPLODE

The Explode command is used to "explode" single objects back to their constituent parts. In other words, the command is used to return blocks, polylines etc. (which may be composed of a number of component objects) back to their individual component parts. The change has no visible effect.

Tips & Tricks

Always look at the command line for guidance when you are learning new AutoCAD commands. The command line will prompt you for information and this is the easiest way to find out how a new command works. This is especially true for the more complicated commands like Trim and Extend.
The command line window displays 3 lines of text by default. You can change this by clicking and dragging the top of the window frame. When you are starting with AutoCAD you may like to see more than 3 lines. The illustration below shows the command line window increased in size to 6 lines.

The command line can also be displayed as a floating text window. The AutoCAD text window is displayed by pressing the F2 key on the keyboard. See Function Keys on the Drawing Aids tutorial for more details.
You can control the way text is mirrored using the MIRRTEXT variable.
You can use the Fillet command with a radius of zero to trim intersecting lines back to their intersection. Of course, you could also achieve this effect with the Trim command but if you have a number of operations to complete, the Fillet method is much quicker.
When using the Trim and Extend commands, hitting when prompted to "Select cutting edges" and "Select boundary edges" respectively will automatically select all valid cutting or boundary edges on the screen. This can be a real time saver if you have a complicated set of edges to select.

Modifying Object: The Fillet Command

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Toolbar	Modify
Pull-down	ModifyFillet
Keyboard	FILLET	short-cut	F

The Fillet command is a very useful tool which allows you to draw an arc between two intersecting lines or adjacent polyline segments. You first need to use the command to set the required radius and then a second time to select the two lines.

Command Sequence

Command: FILLET
Current settings: Mode = TRIM, Radius = 10.0000
Select first object or [Polyline/Radius/Trim]: R
Specify fillet radius <10.000>: 25
Select first object or [Polyline/Radius/Trim]: (pick P1)
Select second object : (pick P2)

The Fillet command can also be used to fillet arcs and circles. The "Polyline" option also allows you to fillet all vertices of a polyline with a single command. It's worth experimenting with this command, it can save you lots of time and enables you to construct shapes which otherwise would be quite difficult.

For example, you can easily create the lozenge shape shown on the right from a simple rectangle. Since AutoCAD rectangles are just closed polylines, you can use the Polyline option of the Fillet command to fillet all polyline vertexes simultaneously. Try this for yourself; draw a rectangle and then follow the command sequence below.

Command Sequence

Command: FILLET
Current settings: Mode = TRIM, Radius = 10.0000
Select first object or [Polyline/Radius/Trim]: P
Select 2D polyline: (pick P1)
4 lines were filleted

Tip: Make sure that the radius you specify will fit the objects you select, otherwise the fillet command will not work.

Modifying Object: The Chamfer Command

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Toolbar	Modify
Pull-down	ModifyChamfer
Keyboard	CHAMFER	short-cut	CHA

The Chamfer command enables you to create a chamfer between any two non-parallel lines as in the illustration below or any two adjacent polyline segments. Usually, the Chamfer command is used to set the chamfer distances before drawing the chamfer. Follow the command sequence below where the chamfer distances are changed to 20 before the chamfer is made.

Command Sequence

Command: CHAMFER
(TRIM mode) Current chamfer Dist1 = 10.0000, Dist2 = 10.0000
Select first line or [Polyline/Distance/Angle/Trim/Method]: D (to set distances)
Specify first chamfer distance <10.0000>: 20 (enter required distance)
Specify second chamfer distance <20.0000>: (first distance value or enter a different value)
Select first line or [Polyline/Distance/Angle/Trim/Method]: (pick P1)
Select second line: (pick P2)
The chamfer is made and the command ends.

Notice from the command sequence that there are a number of options which can be used to control the way the Chamfer command behaves. The Polyline option can be used to chamfer all vertexes of a polyline simultaneously. The Distance option allows you to specify the two chamfer distances. Angle allows the angle between the first line and the chamfer to be specified. Trim is used to control whether the original lines are trimmed to the chamfer or remain as they are. Finally, Method is used to toggle the command between Distance and Angle mode. When Angle mode is used, the chamfer is defined using one distance and an angle rather than two distances.

Modifying Object: The Break Command

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Toolbar	Modify
Pull-down	ModifyBreak
Keyboard	BREAK	short-cut	BR

The Break command enables you to break (remove part of) an object by defining two break points. In the illustration below, a corner of a rectangle has been removed. The Break command can be used with lines, polylines, circles, arcs ellipses, splines, xlines and rays. When you break an object, you can either select the object using the first break point and then pick the second break point, or you can select the object and then pick the two break points.

Command Sequence

Command: BREAK
Select objects: (select the object using the first break point, P1)
Specify second break point or [First point]: (pick the second break point, P2)
The section of the object is removed and the command ends.

Sometimes you may want to select the object first and then specify the two break points. If this is the case, use the "First point" option to specify the first break point. By default, AutoCAD assumes that the point used to select the object is the first break point. This is often confusing for new users.

It may sometimes be necessary to break a line into two without removing any part of it. In this case, simply pick the first and second break points in the same position.

Modifying Object: The Extend Command

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Toolbar	Modify
Pull-down	ModifyExtend
Keyboard	EXTEND	short-cut	EX

This command extends a line, polyline or arc to meet another drawing object (known as the boundary edge). In the illustration on the right, two lines (red) are extended to meet another line (cyan) which forms the boundary edge. This command works in a similar way to the Trim command, described above. Two selections are made, one for the boundary edge(s) and one for the object(s) to extend.

Lines and other objects can be extended in one of two directions. In the illustration on the right, the red line could be extended either to the right or to the left. You can tell AutoCAD in which direction to extend by picking a point to the right or left of the midpoint respectively. AutoCAD does not intuitively know where the boundary edge lies so you must explicitly indicate the direction of extension by picking either one side or other of the midpoint.

Draw the lines as shown in the illustration and follow the command sequence below.

Command Sequence

Command: EXTEND
Current settings: Projection=UCS Edge=None
Select boundary edges ... Select objects: (select the boundary edge, P1)
Select objects: (to end boundary edge selection)
Select object to extend or shift-select to trim or [Project/Edge/Undo]: (pick the object which you want to be extended, P2)
Select object to extend or shift-select to trim or [Project/Edge/Undo]: (pick another object which you want to be extended, P3)
Select object to extend or shift-select to trim or [Project/Edge/Undo]: (to end)

Sometimes you may get the message "Object does not intersect an edge" or "No edge in that direction". If this happens it means that you are either picking the wrong end of the object or the object you are trying to extend will not meet the boundary edge. The solution is either to pick near the end you want to extend or to move the boundary edge so that the extended line will intersect with it.

Using Edgemode

If the line you are trying to extend does not intersect with the boundary line, you can use the "Edge" option to toggle Edgemode to "Extend" (the default is "No Extend"). When the Extend command is set to Extend Mode, the objects being extended will extend to an imaginary line through the boundary edge, irrespective of whether the extended object actually intersects with the boundary edge. This is particularly useful and can save lots of time.

The illustration on the left shows the result of extending a line (red) to a boundary edge (cyan) with Edgemode set to "Extend". The same process would have resulted in an error message if Edgemode had been set to "No Extend". To get a better understanding of how this works, draw the two lines as shown in the illustration and try to extend them using the default settings. When you have done that, follow the command sequence below.

Command Sequence (Edgemode)

Command: EXTEND
Select boundary edges: (Projmode = UCS, Edgemode = No extend) Select objects: (select the boundary edge, P1)
Select objects: (to end boundary edge selection)
Select object to extend or shift-select to trim or [Project/Edge/Undo]: E (to use the Edge option)
Enter an implied edge extension mode [Extend/No extend] : E (to set Edgemode to Extend)
Select object to extend or shift-select to trim or [Project/Edge/Undo]: (pick the object to be extended, P2)
Select object to extend or shift-select to trim or [Project/Edge/Undo]: (to end)

Notice that the current value of Edgemode is always displayed on the command line when you start the Extend command. The Edge option can also be used with the Trim command to enable trimming to cutting edges which do not actually intersect the object to trim. Edgemode is a system variable, so any change to its value will affect both the Trim and Extend commands.

See the Lengthen command for more ways to extend and trim objects.

Shift Selection with Trim & Extend

You may have noticed during the command sequences for the Trim and Extend commands that you have the option to "shift-select". This feature is new to AutoCAD 2000i and it enables you to extend while using the Trim command and to trim while using the Extend command. These two commands are very closely related and you often need to trim and extend objects at the same time. If you are a beginner with AutoCAD it may be a good idea to avoid this feature initially, the Trim and Extend commands can be tricky to get to grips with in any case. However, do remember this feature because it is a great time saver.

Modifying Object: The Trim Command

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Toolbar	Modify
Pull-down	ModifyTrim
Keyboard	TRIM	short-cut	TR

The Trim command can be used to trim a part of an object. In order to trim an object you must draw a second object which forms the "cutting edge". Cutting edges can be lines, xlines, rays, polylines, circles, arcs or ellipses. Blocks and text cannot be trimmed or used as cutting edges. The illustration on the right shows the Trim command in action. The red square and circle have been drawn using the Polygon and Circle commands respectively. In order to trim these objects, a line has been drawn (cyan in the illustration), this forms the cutting edge. The Trim command, unlike most other modify commands requires that two separate object selections are made. The cutting edges are selected first (there can be one or more) and then the objects to be trimmed are selected. In the example above, the line is selected first because it forms the cutting edge and then the square and circle are selected.

The Trim command is slightly more complicated than many other modify commands. To get a better understanding of how it works, draw a square, circle and line as illustrated above and then follow the command sequence below. Don't forget to watch the AutoCAD command line at each stage of the process.

Command Sequence

Command: TRIM
Current settings: Projection=UCS Edge=None
Select cutting edges ... Select objects: (select the cutting edge, P1)
Select objects: (to end cutting edge selection)
Select object to trim or shift-select to extend or [Project/Edge/Undo]:(pick the part of the square which you want to trim, P2)
Select object to trim or shift-select to extend or [Project/Edge/Undo]: (pick the circle, P3)
Select object to trim or shift-select to extend or [Project/Edge/Undo]: (to end)

Notice that at each trimming step you are given the option to undo the previous trim. This can be very useful if you inadvertently pick the wrong object.

In the above example, when the objects were trimmed, both pick points were made to the right of the cutting edge, resulting in the removal of that part of the objects to the right of the cutting edge. Obviously, the portion of square and circle to the left of the cutting edge could have been removed by picking to the left of the cutting edge. Also, you may not have noticed it, but by trimming a circle you have created an Arc object. This makes no visible difference but the object type has changed.

Modifying Object: The Lengthen Command

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Toolbar	Modify
Pull-down	ModifyLengthen
Keyboard	LENGTHEN	short-cut	LEN

The Lengthen command can often be used instead of either the Trim or Extend commands. Indeed the end result is exactly the same. The Lengthen command can be used to either lengthen or shorten Lines, Arcs, open Polylines, elliptical Arcs and open Splines without the use of cutting or boundary edges.

Command Sequence

Command: LENGTHEN
Select an object or [DElta/Percent/Total/DYnamic]: DY
Select an object to change or [Undo]: (select a line or arc)
Specify new end point: (pick new end point)
Select an object to change or [Undo]: (to end)

The command sequence above demonstrates the use of the Dynamic Lengthen option which is probably the most useful for general purpose drafting. However, the other options are worth getting to know because they can save lots of time and effort.

The Total option allows you to change the total length of a line to any value that you specify. The Percent option allows you to change a line length using a percentage. For example, a value of 50 will result in a line one half the length of the original and a value of 200 will result in a line twice the length of the original. The Delta option can be used to extend or reduce the endpoint of a line by a given distance. The endpoint affected by the change is the one closest to the pick point when the object selection is made.

Modifying Object: Stretching with Grips

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Although the Stretch command can be very useful, it has largely been superseded by the use of "Grips" which allow this sort of modification to be made much more intuitively.

To stretch an object using grips, simply select the object by clicking on it (you can do this without starting a command). The object becomes highlighted and small square grips appear at each vertex and various snap points, depending upon the object type. Click a grip to activate it and click again to reposition it. When you have completed your modifications, use the Escape key (Esc) at the top left of your keyboard to deselect the object and release grips.

Modifying Object: The Stretch Command

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Toolbar	Modify
Pull-down	ModifyStretch
Keyboard	STRETCH	short-cut	S

The Stretch command can be used to move one or more vertices of an object whilst leaving the rest of the object unchanged. In the example below, a rectangle has been stretched by moving one vertex to create an irregular shape.

Command Sequence

Command: STRETCH
Select objects to stretch by crossing-window or crossing-polygon...
Select objects: (pick first point of crossing window)
Specify opposite corner: (pick second point of window)
Select objects: (to end selection)
Specify base point or displacement: (pick base point)
Specify second point of displacement: (pick second point)

To select vertices to stretch, you must use a crossing window or polygon. See the "Object Selection" tutorial for details of these selection methods.

Modifying Object: The Scale Command

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Toolbar	Modify
Pull-down	ModifyScale
Keyboard	SCALE	short-cut	SC

The Scale command can be used to change the size of an object or group of objects. You are prompted for a pick point about which the selection set will be scaled. Scaling can then be completed by picking a second point (not always easy because it can sometimes be difficult to precisely control the scaling) or by entering a scale factor at the keyboard. For example a scale factor of 2 will double the size of the objects in the selection set and a factor of 0.5 will half them.

Command Sequence

Command: SCALE
Select objects: (pick objects to be scaled, P1)
Select objects: (to end selection)
Specify base point: (pick base point, P2)
Specify scale factor or [Reference]: (pick second point, P3 or enter scale factor)

In the example shown above, the original tree symbol has been enlarged by dynamically scaling it using pick points to determine the change in scale. If you want to scale an object precisely, it is much easier to enter a scale factor using the keyboard.

Note that the position of the new sized tree symbol is determined by the location of the base point. The base point, P2 has been picked to the upper right of the centre of the tree which resulted in the centre of the tree shifting to a lower left position. If the base point had been picked in the centre of the tree symbol, the tree would have remained in the same position. In theory the base point can be any point in the drawing area but for ease of control it is best to choose a known point so that the results are obvious.

Modifying Object: The Rotate Command

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Toolbar	Modify
Pull-down	ModifyRotate
Keyboard	ROTATE	short-cut	RO

The Rotate command allows an object or objects to be rotated about a point selected by the user. AutoCAD prompts for a second rotation point or an angle which can be typed at the keyboard.

Command Sequence

Command: ROTATE
Current positive angle in UCS: ANGDIR=counterclockwise ANGBASE=0
Select objects: (pick object to rotate, P1)
Select objects: (to end selection)
Specify base point: (pick base point, P2)
Specify rotation angle or [Reference]: (pick second point, P3 or enter angle)

Remember, by default, AutoCAD angles start at 3 o'clock and increase in an anti-clockwise direction. The "ANGDIR" and "ANGBASE" variables remind you of this. If you want to rotate in a clockwise direction you can enter a negative angle by using a minus sign.

Note: You can change the angle direction and the base angle using the Units command, FormatUnits… from the pull-down menu. Click the "Clockwise" check box to change the direction and click the "Direction…" button to set the base angle.

Modifying Object: The Move Command

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Toolbar	Modify
Pull-down	ModifyMove
Keyboard	MOVE	short-cut	M

The Move command works in a similar way to the Copy command except that no copy is made, the selected object(s) is simply moved from one location to another.

Command Sequence

Command: MOVE
Select objects: (pick object to move, P1)
Select objects: (to end selection)
Specify base point or displacement: (pick P2)
Specify second point of displacement or : (pick P3)

Note that as with the Copy command, the two pick points, P2 and P3 are used only to indicate the distance and direction of movement.

Modifying Object: The Array Command

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Toolbar	Modify
Pull-down	ModifyArray
Keyboard	ARRAY	short-cut	AR

The Array command makes multiple copies of selected objects in a rectangular matrix (columns and rows) or a polar (circular) pattern. This command has been completely transformed in AutoCAD 2000i. It is now completely dialogue box driven with the option to see a preview of the array before it is created. You can also now create rectangular arrays at a user specified angle angle. This constitutes a major improvement in usability.

The Rectangular Array

The illustration on the right shows the results of a rectangular array with two columns an three rows. The distance between rows is indicated with the dimension DR and between columns with DC. When creating rectangular arrays it is important to remember that new rows are created above the original object and new columns are created to the right of the original object. The resulting array is, therefore, always created with the original object in the bottom left hand position with respect to the current co-ordinate system. In the illustration, the original object is shown in cyan and the new objects in red. It is possible to create arrays which do not align with the World Co-ordinate System by setting a User Co-ordinate System first. See the UCS tutorial for details.

Try creating this array yourself. First, draw a rectangle 20 drawing units wide and 10 drawing units tall. To do this, start the rectangle command DrawRectangle from the pull-down menu. When you are prompted to pick a point, pick somewhere in the lower left quarter of the drawing area. Then, when you are prompted for a second point, enter the relative cartesian co-ordinate @20,10. You have now drawn a rectangle at the right size. See the Using Co-ordinates tutorial for more information on drawing with co-ordinates.

Now start the Array command.First of all, make sure that the Rectangular Array radio button is selected and that you are looking at the Rectangular Array dialogue box and now follow the steps below:

Click the Select objects button. The dialogue box will temporarily disappear enabling you to select the rectangle you just drew. Press the Return button on your keyboard to complete the selection. You are now returned to the dialogue box and the message immediately below the Select Objects button should read "1 objects selected".
Enter the number of rows required in the Rows edit box. For this example, enter the value "3". Notice that the schematic preview on the right hand side of the dialogue box updates to reflect the values you are entering.
Enter the number of columns required in the Columns edit box. Enter the value "2".
Enter the row offset in the Row Offset edit box. This is the distance DR in the illustration above. Note that tis is not the distance between rows. In this example, our rectangle is 10 units high and we will enter a row offset of 15. The result will be a 5 unit gap between rectangles.
Enter the column offset in the Column Offset edit box. The same parameters apply as for the row offset. Enter a value of 25 to give a 5 unit gap between our rectangles.
Click on the Preview button. Once again, the dialogue box disappears and the specified array is temporarily drawn so that we can preview it. We are now offered 3 choices. If the array isn't quite right, click the Modify button to return to the Array dialogue box. If you are happy with the array, click the Accept button, the array will be permanently drawn and the command is ended.

You should now have an array that looks similar to the one in the illustration above consisting of 6 rectangles arranged in 3 rows and 2 columns. As you can se, this command is very powerful and can save lots of time if used carefully.

The Polar Array

The polar array works in a similar way to the rectangular array. The main difference is that rather than specifying the number and offset for rows and columns, you must specify a center point and the total number of objects in the array (including the original object).

You can try this for yourself by drawing another rectangle as described above. This time, though, locate the rectangle in the centre top half of the drawing area. Now, start the Array command, click the Polar Array radio button and follow the steps below:

Click the Select objects button. The dialogue box will temporarily disappear enabling you to select the rectangle you just drew. Press the Return button on your keyboard to complete the selection. You are now returned to the dialogue box and the message immediately below the Select Objects button should read "1 objects selected".
Specify the center point for the array. This is the point C in the illustration below. You can do this by entering x and y co-ordinates into the appropriate edit boxes if you know what these values should be. However, this is rarely the case and most often you will want to click the Pick Center Point button to pick a point from the drawing area. Pick a point somewhere below the rectangle you have just drawn.
Enter a value for the total number of items. For this example, enter the value "6". Notice that once again, the schematic preview updates to reflect the values you have entered.
Make sure that the Rotate items as copied checkbox is checked.
Click on the Preview button. Once again, the dialogue box disappears and the specified array is temporarily drawn so that we can preview it. We are now offered 3 choices. If the array isn't quite right, click the Modify button to return to the Array dialogue box. If you are happy with the array, click the Accept button, the array will be permanently drawn and the command is ended.

The array you have just drawn should look something like the one illustrated below, left. Take some time to play around with the other options in the Array dialogue box to see what they can do.

The illustration above shows the results of a polar array using an original rectangle (cyan) copied six times about a centre point C, through an angle of 360 degrees (full circle). The only difference between the array on the left and the one on the right is that the Rotate items as copied checkbox was not checked in the right hand example.

All new objects created with the Array command will inherit the object properties of the original object. See the "Object Properties" tutorial for information on object properties.

Modifying Object: The Offset Command

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Toolbar	Modify
Pull-down	ModifyOffset
Keyboard	OFFSET	short-cut	O

Offset is probably one of the most useful commands for constructing drawings. The Offset command creates a new object parallel to or concentric with a selected object. The new object is drawn at a user defined distance (the offset) from the original and in a direction chosen by the user with a pick point. You can offset lines, arcs, circles, ellipses, 2D polylines, xlines, rays and planar splines.

Command Sequence

Command: OFFSET
Specify offset distance or [Through] <1.0000>: 10 (specify distance)
Select object to offset or : (select object, P1)
Specify point on side to offset: (pick direction, P2)
Select object to offset or : (to end or select another object to offset)

In the illustration below, a line (cyan) has been offset to the right through a distance "Offset" by picking a point to the right of the original line. The result is a new line (red) to the right of the original.

Circles can be offset inside or outside of themselves to create a new circle which is concentric (has the same centre point) with the original circle. In the illustration, a new circle (red) has been created outside of the original by picking a point outside of the original circle. The radius of the new circle is the offset distance "Offset" plus the radius of the original circle.

In the illustration above, the new objects and original objects are shown in different colours for clarity. In reality, offset objects inherit their object properties from the original object. See the "Object Properties" tutorial for details.

Modifying Object: The Mirror Command

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Toolbar	Modify
Pull-down	ModifyMirror
Keyboard	MIRROR	short-cut	MI

The Mirror command allows you to mirror selected objects in your drawing by picking them and then defining the position of an imaginary mirror line using two points.

Command Sequence

Command: MIRROR
Select objects: (pick object to mirror, P1)
Select objects: (to end selection)
Specify first point of mirror line: (pick P2)
Specify second point of mirror line: (pick P3)
Delete source objects? [Yes/No] : (for No to keep the original object)

Notice that in the command sequence above, pressing the key when asked whether to "Delete source objects?" resulted in a "No" response. This is because "No" is the default option. AutoCAD always shows the default option within triangular brackets, in this case "". Many AutoCAD commands offer default options. They are usually the most commonly used and you need only right-click and select "Enter" from the menu or press on the keyboard to accept them.

In order to create perfectly horizontal or vertical mirror lines use Ortho. For more information on the use of Ortho and other drawing aids, see the "Drawing Aids" tutorial.

Modifying Object:The Copy Command

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Toolbar	Modify
Pull-down	ModifyCopy
Keyboard	COPY	short-cut	CP

The Copy command can be used to create one or more duplicates of any drawing object or objects which you have previously created. Copy is a very useful and time-saving command because you can create very complex drawing elements and then simply copy them as many times as you like.

Command Sequence

Command: COPY
Select objects: (pick object to copy, P1)
Select objects: (to end selection)
Specify base point or displacement, or [Multiple]: (pick P2 or M for multiple copies)
Specify second point of displacement or : (pick P3)

The multiple option allows you to create additional copies of the selected object(s) by picking as many new points as you like. To end a multiple copy, just hit the key.

Notice that the "Base point", P2 and the "Second point", P3 do not have to be picked on or near the object. The two points are simply used to indicate the distance and direction of the copied object from the original object.

The Erase Command

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Toolbar	Modify
Pull-down	ModifyErase
Keyboard	ERASE	short-cut	E

The Erase command is one of the simplest AutoCAD commands and is one of the most used. The command erases (deletes) any selected object(s) from the drawing. Remember you can always get deleted objects back by typing U to undo, from the Standard toolbar or by using the OOPS command.

Command Sequence

Command: ERASE
Select objects: (pick an object to erase)
Select objects: (to end the selection and erase the object)

If you simply want to erase the last object you created you can type L at the "Select objects" prompt. The last object will be highlighted and you can then select more objects or to end the command. See the "Object Selection" tutorial for more information on selecting objects.

Introduction Modifying Objects

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AutoCAD drawings are rarely completed simply by drawing lines, circles etc. Most likely you will need to Modify these basic drawing objects in some way in order to create the image you need. AutoCAD provides a whole range of modify tools such as Move, Copy, Rotate and Mirror. As you can see, the command names are easily understandable. However, the way these commands work is not always obvious. This tutorial is designed to show you how all of the Modify commands work. If you just need information quickly, use the QuickFind toolbar below to go straight to the information you need or select a topic from the contents list above.

As is usual with AutoCAD, the Modify tools can be accessed in one of three ways, from the keyboard, from the pull-down menu and from the toolbar. All of the Modify tools are available from the Modify pull-down and the Modify toolbar. In each section below, the toolbar, pull-down and keyboard options are given. The method you choose is entirely up to you. Ultimately you will use the method that you feel most comfortable with or the one you find most efficient. AutoCAD allows great flexibility and there aren't any right or wrong ways of working. That said, it should be pointed out that the use of toolbars in AutoCAD is almost always quicker than any other method.

The Modify toolbar is usually displayed by default but if it is not already displayed, you can display it using the TOOLBAR command, ViewToolbars… from the pull-down menu. When the Toolbar dialogue box (shown above) appears, simply check the box next to "Modify" in the toolbars list. Many AutoCAD users work with the Modify toolbar permanently docked on their screen because it gives one-click access to all of the commands, making the drawing process much more efficient.

Crossing Polygon Selection

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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 "". 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 , AutoCAD responds "", 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 to complete the selection process and to continue with the current command.

When you feel confident with the basic selection tools, have a look at the Advanced Selection tutorial to find out how to use AutoCAD's advanced selection tools for creating complex selection sets.

Tips & Tricks

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.

Window Polygon Selection

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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)
Specify endpoint of line or [Undo]: (pick second point)
Specify endpoint of line or [Undo]: (pick third point)
Specify endpoint of line or [Undo]: (pick another point or to end polygon selection)
Select objects: ( to complete the selection set or add more objects)

A polygon is formed by picking at least three points.

Fence Selection

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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)
Specify endpoint of line or [Undo]: (pick second point)
Specify endpoint of line or [Undo]: (pick another point or to end fence selection)
Select objects: ( to complete the selection set or add more objects)