Resizing Objects

A number of commands can be used to modify existing objects. The commands that can be used to resize objects are SCALE, STRETCH, LENGTHEN, TRIM, EXTEND, and BREAK, all of which are covered in this section. These commands are located on both the Modify toolbar and the Modify pull-down menu.

Scaling Objects

The SCALE command is used to scale objects up or down in size. This command employs the general selection process, which gives you many options for selecting the objects. After selecting the objects to be scaled, you are prompted to pick a base point. You then can enter a scaling factor or graphically pick a distance, or you can specify the Reference option. When you graphically scale the selection set, the length of the rubberband line is used as the scaling factor.

The Reference option of the SCALE command provides a very useful control. After you request that option, you are prompted to specify a reference length. You usually specify it graphically along an existing object or distance. You are then prompted for a new length value. This makes it very easy to scale an unknown distance to a known distance.

Stretching Objects

The STRETCH command is used to stretch an object’s length by relocating a portion of the object. Although the command does issue the general Select Objects: prompt, you must select the desired objects using one of the crossing selection methods (an implied crossing window, a crossing window, or Cpolygon). You can use only one crossing window per occurrence of the STRETCH command. If you define more than one crossing window in a single STRETCH command sequence, only the objects selected with the last crossing window are stretched.

After you select the objects, you are prompted to select a base point or enter a displacement. If you choose to pick a base point, you also must specify a second point for the new location of the base point. As an alternative to picking a base point, you can specify a displacement.

The displacement is defined as the delta-X, delta-Y, and delta-Z—or the distance and angle from the start point to the endpoint, which is essentially the distance the object(s) are to be stretched and the direction you want to apply to the objects. If you know the exact displacement you want to use, you can enter the displacement at the prompt for the base point and press Enter twice. The displacement you enter can be an absolute Cartesian coordinate, a relative distance from the base point, or a polar coordinate. The STRETCH command will move all objects that are completely enclosed in the crossing window. Any objects not completely enclosed within the crossing window are stretched by repositioning those endpoints inside the crossing window while maintaining the position of those endpoints outside the crossing window.

Trimming Objects

With the TRIM command, you begin the trimming process by selecting the object(s) that will define the “cutting edge,” then selecting the object(s) to be trimmed against the selected cutting edge(s), selecting those objects which are to be trimmed away or removed. If you want to select more than one object at a time, you can use the Fence option to select multiple cutting edges or multiple objects to be trimmed. The TRIM command is effective only if an object is left over; otherwise, the ERASE command should be used.

Any edge object, such as a line or a circle, can be used as a cutting edge or can be the object to be trimmed. However, an Mline object can be selected as a cutting edge but cannot be trimmed. It’s worth mentioning that when you’re trimming out a segment of a circle, after the first trim, the object is converted into an arc object. When you use the TRIM command, the result depends on the point you selected on the object being trimmed (see Figure 10.10).

An enhancement added in AutoCAD 2000i was the ability to TRIM and EXTEND to objects contained in blocks or xrefs.

Starting from the point that is used to select the object, use the TRIM command to proceed in one direction along the object until you encounter either an endpoint or a cutting edge. Then the TRIM command proceeds from the original pick point in the opposite direction until it encounters either an endpoint or another cutting edge. The resulting defined portion of the object is then removed. Under no circumstances can an object be trimmed in such a way that nothing is left of the object. This condition exists when you trim a circle with a cutting edge that does not cross the circle completely.

Extending Objects

The EXTEND command is used to elongate an edge object to an existing boundary (see Figure 10.11).

EXTEND is the complement to the TRIM command, so it has the same options. Instead of prompting you to select the cutting edge(s), the EXTEND command prompts you to select the boundary edge(s). The Project and Edge options are settings saved and shared by the TRIM and EXTEND commands.

Another enhancement made to the TRIM and EXTEND commands is the capability to switch between modes while in either command. While in the TRIM command if you hold down the Shift key any objects you select will be extended to your “cutting edge” objects, if possible. When you release the Shift key you return to the TRIM command mode. You may find this feature easier to utilize if you do not define a cutting edge selection so that you can use all drawing entities as edges.

Using the Edge Option to Extend the Cutting Edges

By default, the object to be trimmed must physically intersect the cutting-edge object. You can bypass this requirement with the Edge option. Choosing the Extend mode of the Edge option extends the cutting edges so the object(s) being trimmed need not intersect the cutting edge.

Choosing the Edge option to Extend sets the EDGEMODE system variable to 1. This option controls just how the TRIM and EXTEND commands find cutting and boundary edges. With a setting of 0, it uses the selected edge without any implied extension. With a setting of 1, it extends or trims the selected object to an implied extension of the selected cutting or boundary edge. This system variable can be used with the TRIM and EXTEND commands. When the setting has been made in either command, it affects the operation of both.

Breaking Objects

To remove a portion of an object, consider using the BREAK command. BREAK offers two advantages over TRIM for removing a portion of an object. First, you do not need any cutting objects to use BREAK. Second, the BREAK command can be used to break a non-closed object into two objects without removing any part of the original single object.

After you select the object to be broken, the default option requests a second point on the object. Then the portion of the object between the point used to select the object and the second point is removed. Notice that when you first select the object to break, it’s not necessary to press Enter to go to the next prompt.

Sometimes, however, the point used to select the object is not where you want to begin the break. In such a case, you would use the First option to specifically define the beginning point of the break and the second point of the break.

When you use BREAK, sometimes the second point that you selected for the end of the break (or the two points you pick for the First option) does not actually lie on the object to be broken. In this case, the point is projected perpendicularly back to the object, and the projected point is used as the end of the break (see Figure 10.12).

If you simply want to break an object into two objects without actually removing a portion of the object, define the second point at the same location as the first point of the break. The easiest way to do this is to enter @ as the second point. When you enter @, AutoCAD passes the last point recorded directly into the current request for a point location.

In the following exercise, you explore the various methods of resizing objects in AutoCAD. These commands will enable you to edit existing objects instead of erasing and creating new ones.

Exercise 10.3 Editing Existing Objects

1.	Open CHAP10-1.dwg from the CD if it’s not open from the previous exercise. Choose Named Views from the View pull-down menu. Then select the view named OFFICE-D, click on the Set Current button in the View Control dialog box, and click OK to display the view shown in Figure 10.13. Figure 10.13. The area of the drawing used in the edit exercise.
2.	To use the UNDO command and place a marker with the Mark option, type UNDO at the Command: prompt, press M , and press Enter. This will enable you to restore the drawing after the exercise is complete.
3.	From the Modify pull-down menu, select the Scale menu option. At the Select Objects: prompt, window the collection of chairs and desks in the center of the room.
4.	At the Specify base point: prompt, choose the intersection of the blue walls at the center of the room. It is not critical to choose the exact center; just eyeball the point.
5.	At the Specify scale factor or [Reference]: prompt, type in a scale of 1.2 . This enlarges the object collection 120%.
6.	From the Modify pull-down menu, select the STRETCH command. At the Select Objects: prompt, pick a point near , followedby , as shown in Figure 10.14. This selects the end of the wall at the bottom of the room. Figure 10.14. The points needed to stretch the wall.
7.	At the Specify base point or displacement prompt, pick at . Then, at the Specify second point of displacement: prompt, type @15'<0 to shorten the wall to near to the column to the right.
8.	From the Modify pull-down menu, select the EXTEND command. At the Select boundary edges: prompt, press Enter. For this exercise, you will not select objects; instead, you will have AutoCAD select all objects for use.
9.	At the Select object to extend or shift-select to trim or [Project/Edge/Undo] prompt, pick the two lines that make up the wall to the right. Choose near point , and then press Enter. The wall lines now extend to close the wall. Note With the introduction of AutoCAD 2000i came an enhancement to the TRIM and EXTEND commands. Now either command is available while running the other. If you are using the TRIM command and selecting objects in which to trim, pressing the Shift key as you pick extends rather than trim. The opposite is also true while using the EXTEND command; pressing Shift while you select objects to extend will trim them instead. This can be a big timesaver once you get the hang of it.
10.	From the Modify pull-down menu, select the TRIM command. At the Select cutting edges: prompt, press Enter. You will again use all objects for trim edges.
11.	At the Select object to trim or shift-select to extend or [Project/Edge/Undo] prompt, choose the two lines at . The wall lines will once again open the room.
12.	From the Modify pull-down menu, choose Break.
13.	At the Select Objects: prompt, choose the inside wall line at the top of the room. Pick a point at . This selects the object to be broken.
14.	At the Specify second break point or [First point]: prompt, type F . This allows you to fully define the points at which to break.
15.	At the Specify first break point: prompt, use the Center Osnap and choose the upper-left chair in the room.
16.	At the Specify second break point: prompt, use the Center Osnap again to choose the upper-right chair in the room. A portion of the wall is removed using the X coordinates of the two chairs. To see the power of the UNDO command again, enter UNDO and BE for “begin,” and all changes you made in this exercise will be undone. You can leave this drawing open for the following exercise.

Sometimes the problems with your objects are not their physical properties but their locations. The following section covers commands for repositioning objects.