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Inside AutoCAD 14

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- 11 -

Advanced Geometry Editing

by Francis Soen

In the previous chapter, "Basic Object Editing," you learned the basic commands and tools needed to make changes to existing objects. In this chapter, you build on that foundation and learn about the following topics:

Beveling Corners

If your design requires you to draw a beveled corner, use the CHAMFER command. The CHAMFER command is used to bevel corners formed by two nonparallel lines, rays, xlines, or line segments of a polyline. The command is issued by choosing Chamfer from the Modify pull-down menu or toolbar. To use the CHAMFER command, you first set the parameters defining the bevel to be generated, and then select the two line segments that form the corner.

Defining the Bevel

To obtain the desired bevel, you first define one of two sets of parameters. One set of parameters, accessed with the Distances option, enables you to define the beveling operation with two distances, one along the first selected line and the other along the second selected line. Both distances are measured from the corner, or intersection, of the two lines (see fig. 11.1).

Figure 11.1 The Distance option enables you to define the bevel with distances measured from the intersection of two selected lines.

The other set of parameters, accessed with the Angle option, consists of a distance measured from the corner point along the first selected line and the angle of the new line relative to the first selected line (see fig. 11.2).

Figure 11.2 The Angle option enables you to define the bevel with a distance and an angle.

You can use either or both of the Distances and Angle options, depending on what design information is available to you. The CHAMFER command utilizes the most recently defined set of parameters. If both sets of parameters are defined, you can switch between them by using the Method option.

TIP: When you select either the Distances or the Angle option and set the parameters, the CHAMFER command ends. You must repeat the command and select the two line segments to produce the bevel. Remember, a quick way to repeat the last command issued is to press the spacebar or the Enter key at the Command: prompt.

The two lines you bevel do not have to intersect at a corner point. CHAMFER automatically trims or extends the two lines to a corner point before generating the bevel line. A quick way to trim or extend two lines to a corner point is to use the CHAMFER command with the distances set to zero (see fig. 11.3).

Figure 11.3 Using CHAMFER with zero distances trims or extends two lines to a corner point.

If the two lines selected are on the same layer and have identical color and linetype properties, the new bevel line is drawn with the same properties. If there is a difference in a particular property of the two selected objects, then the bevel line takes on the current value of that object property. For example, if the two selected lines are drawn on different layers, then the new bevel line is drawn on the current layer. If the two selected lines are drawn with a different color, then the bevel line is drawn with the current color property. If the two selected lines are drawn with a different linetype, then the bevel line is drawn with the current linetype property.

NOTE: If two objects are drawn on two different layers and are displayed in two different colors, it does not mean that the color property of the two objects is different. If the two layers have different colors assigned to them and the color property of the two objects is BYLAYER, then the two objects are drawn with the color assigned to the layer the objects reside on. Obviously, if the two layers have different assigned colors, the BYLAYER color setting results in the objects being drawn in two different colors; however, both objects have the identical BYLAYER color property. The BYLAYER setting also affects the linetype used to display objects in the same manner.

Dealing with Polylines

To bevel all the corners of a polyline simultaneously, specify the Polyline option and select the target polyline. Be aware, however, that when you generate a bevel line at any angle other than 45° relative to the selected lines, the result will not be symmetrical (see fig. 11.4).

Figure 11.4 Using the Polyline option simultaneously bevels all the corners of a rectangle drawn with RECTANG, but the result can be asymmetric.

This asymmetric result is produced because the polyline segments are processed in the order in which they are drawn. To produce a symmetrical beveled shape, you must bevel one corner at a time. By explicitly selecting the first and second line segments, you control how much each segment is trimmed.

To Trim or Not to Trim

As previously stated, by default, CHAMFER extends or trims the lines to a corner point before applying the chamfer distances and/or angle. If, however, you want to draw the bevel line without any modifications to the original lines, choose the Trim option. At this point, you may choose between either the Trim or No trim settings. If you do not want the original lines modified, then choose the No trim setting. In the following exercise, you use the CHAMFER command to bevel the corners of a rectangle.

BEVELING THE CORNERS WITH CHAMFER

1. Open the drawing MODIFY2.DWG in the Chapter 11 Exercise folder on the accompanying CD. This drawing contains Plan and Elevation views of a part. Using CHAMFER, you are going to bevel the corners in the Plan view.

2. Choose Chamfer from the Modify toolbar or drop-down list, choose Angle, and set the chamfer distance to 1 and the chamfer angle to 45 degrees.

3. Repeat the CHAMFER command, this time choosing the Polyline option and selecting the rectangle in the Plan view. Note how all the corners are beveled in one operation.

4. Choose Undo from the Standard toolbar to undo the CHAMFER command. The rectangle is restored to its original shape.

5. Repeat the CHAMFER command. Select the two lines that form the upper-left corner of the rectangle (see fig. 11.5). Repeat the CHAMFER command, and then select the two lines that form its upper-right corner. The two top corners are now beveled at a 45° angle.

6. Repeat the CHAMFER command, this time specifying the Distances option. Then set the first distance to 1.0 and the second distance to 0.5.

7. Repeat the CHAMFER command, and select the lines that form the lower-left corner with 1 and 2. Then repeat the CHAMFER command, and select the lines that form the lower-right corner with 3 and 4. Remember--the order in which you select the lines is important.

8. Save the drawing. Your rectangle should resemble the one in figure 11.5. (This drawing is used in the next exercise so keep it open.)

Figure 11.5 Beveling the corners of the rectangle.

Filleting Objects

If your design requires that you draw a rounded corner, then use the FILLET command. FILLET is issued by choosing Fillet from the Modify pull-down menu or toolbar. With FILLET, you not only can create rounded corners between two lines, rays, xlines, or line segments of a polyline, but also simply draw an arc segment between any combination of two lines, rays, xlines, circles, ellipses, arcs, elliptical arcs, or splines. The generated arc is always drawn such that it starts and ends tangent to the two selected objects.

Controlling the Operation

To draw the arc, you first use the Radius option to set the radius, and then you select the two objects. As with CHAMFER, if the two objects are nonparallel lines, the lines are trimmed or extended to a corner point, and the arc is drawn such that the tangent lengths are equal (see fig. 11.6).

Figure 11.6 FILLET draws an arc joining two nonparallel lines.

With the FILLET command (unlike the CHAMFER command), the two lines do not have to be nonparallel lines. If the lines are parallel, FILLET automatically draws a semicircle between the ends of the two lines, using the endpoint of the first selected line to determine how far to trim or extend the second selected line (see fig. 11.7). The radius of the generated semicircle is set automatically to half the distance between the two parallel lines.

As mentioned earlier, you can use FILLET for more than just working on lines. Figure 11.8 shows some of the possible combinations of objects on which you can use FILLET, and the effect of the command.

Figure 11.7 FILLET draws a semicircle between the ends of two parallel lines, using the endpoint of the first line to determine where to trim the second line.

Figure 11.8 FILLET can be used with many objects other than lines.

Using FILLET with any objects other than line objects (such as arcs) can produce surprising results (see the two arcs in fig. 11.8). The governing rule is that the generated arc must be drawn in such a way as to start and end tangent to the two selected objects.

If the two selected objects reside on the same layer and have identical color and linetype properties, the new arc is drawn with those properties. If there is a difference in a particular property of the two selected objects, then the arc takes on the current value of that object property. For example, if the two selected objects are drawn on different layers, then the new arc is drawn on the current layer. If the two selected objects are drawn with a different color, then the arc is drawn with the current color property. If the two selected objects are drawn with a different linetype, then the arc is drawn with the current linetype property.

TIP: After you choose the Radius option and set the radius, the FILLET command (like the CHAMFER command) ends. To select the objects, you must repeat FILLET. An easy way to do this is by pressing the spacebar or the Enter key.

A quick and easy way to extend or trim two lines to a corner point is to use FILLET with a zero radius.

Working with Polylines

If you want to round all the corners of a polyline simultaneously, first choose the Polyline option and then select the polyline. If an arc segment separates two line segments, the arc segment is automatically removed and then replaced by the new arc generated by FILLET.

Using the FILLET Command

Generally, if you use FILLET on two objects that are not closed (such as on any object other than a circle or ellipse), the two objects are trimmed or extended as necessary so that the arc can be drawn correctly. If you do not want the original objects to be trimmed, choose the Trim option, and then choose No Trim. This Trim option is the same as the Trim option in the CHAMFER command. This setting is common to both commands, so setting Trim in FILLET affects CHAMFER, and vice versa.

In the following exercise, you use the FILLET command to round off the sharp corners in the drawing MODIFY2.

USING FILLET TO ROUND OFF SHARP CORNERS

1. Continue to use the drawing MODIFY2.DWG. Choose FILLET from the Modify toolbar or pull-down menu.

2. Specify the Radius option, and type 0.5.

3. Repeat the FILLET command. Specify the Polyline option and pick 1 (see fig. 11.9).

4. Repeat the FILLET command, and pick 2 and 3. Repeat the FILLET command, this time picking 4 and 5.

5. Repeat the FILLET command. Specify the Trim option, choose the No Trim setting, and pick 6 and 7.

6. Repeat the FILLET command, this time picking 8 and 9.

7. Choose Trim from the Modify toolbar or pull-down menu. Select (as the cutting edges) the last two arcs you drew with the FILLET command. Trim the two vertical lines by picking 0 and k.

8. Save the drawing, and close the file. You have finished rounding the corners and modifying this drawing. (You are done modifying this drawing so go ahead and close it.)

Figure 11.9 Rounding the corners with FILLET.

Exploding Objects

Several objects are considered compound objects--the objects themselves are composed of other AutoCAD objects. Compound objects can be exploded, or broken down, into their constituent parts with the EXPLODE command. You usually explode a compound object in order to modify one or more of its constituent objects in a way that you cannot do with the compound object itself.

EXPLODE is issued by choosing Explode from the Modify pull-down menu or toolbar. Table 11.1 lists the types of 2D compound objects covered in this book (with appropriate chapter references), and describes briefly how EXPLODE affects the objects, and some reasons why you would consider exploding the object.

Table 11.1 2D Compound Objects and EXPLODE

Object Type Result of EXPLODE
Block insertions An insertion of a block is replaced with duplicates of the block's component objects. Component objects originally drawn on Layer 0 are redrawn onto Layer 0.
A block insertion is usually exploded because you want to modify the component objects themselves. This is usually, but not always, done in the context of redefining the block definition. See Chapter 12, "Creating and Using Blocks," for more information.
Dimensions A dimension is replaced by a combination of lines, mtext, points, solids, and block insertions. Dimensions usually are exploded so that you can further manipulate their component objects. Generally, because exploded dimensions are no longer associative, you should avoid exploding dimensions. For information about dimensions, see Chapter 18, "Productive Dimensioning," and Chapter 19, "Advanced Dimensioning."
Hatch Hatch is replaced by its component lines. An exploded hatch is no longer associative. Again, because of the loss of associativity, exploding a hatch is normally not a good idea. Hatching is covered in Chapter 17, "Drawing Hatch Patterns."
Mline An mline is replaced by its component lines. In this way, you can work around editing commands, such as Extend and Trim, that don't work with mlines. By replacing the Mline object with its component lines, you then can trim or extend those lines. Mlines are covered in Chapter 9, "Creating Complex Objects."
Polylines A polyline is replaced by a series of lines and arcs. If the polyline has a width, the replacement lines and arcs will have no width. Polylines are drawn with the PLINE, POLYGON, RECTANG, and DONUT commands, which are covered in Chapters 7, "Creating Elementary Objects," and 8, "Creating Polylines and Splines."
Region A region is replaced by the edge objects (such as lines and circles) that define the loops (closed shapes) in the region. Regions are covered in Chapter 9, "Creating Complex Objects."

TIP: An exploded object can only be returned to its original unexploded form by using the U or the UNDO commands.

Using Bonus Tools

In addition to the standard editing commands discussed in this chapter and the last, AutoCAD provides a group of "bonus" commands, some of which are useful for modifying existing objects. If you do not have a pull-down menu labeled Bonus, or a Bonus toolbar, you have to install the routines. To do so, follow these steps:

1. Add the \ACADR14\BONUS\CADTOOLS directory to the support file search path in the Preferences dialog box.

2. Add the following line to the end of the file ACADR14.LSP, located in the \ACADR14\SUPPORT directory.

(if (findfile "ac_bonus.lsp") (load "ac_bonus"))

3. Exit AutoCAD, and start the program again to ensure that the changes you performed in steps 1 and 2 take effect.

4. At the Command: prompt, type BONUSMENU. This command should add the Bonus pull-down menu to the current menu, and display the new Bonus toolbars (three in all).

All the commands covered in this section are located in the Modify submenu of the Bonus pull-down menu, or on the Bonus standard toolbar.

Extended Change Properties

To change the properties of objects, you usually select the objects at the Command: prompt, and then set the desired layer, color, and linetype properties through the Properties toolbar. The DDCHPROP2 command comes in handy for setting other properties. To use this command, choose Extended Change Properties on the Properties toolbar to display the Change Properties dialog box (see fig. 11.10).

Using the Change Properties dialog box, you can change not only the layer, color, and linetype properties, but also the object's linetype scale and thickness (for 3D work only). You can also change a polyline's width and elevation, and the height and style of text, mtext, or an attribute definition.

Figure 11.10 The Change Properties dialog box is displayed by the DDCHPROP2 command.

Multiple Entity Stretch

The standard STRETCH command (not the Grip Stretch command) affects only the objects selected with the last crossing window or polygon. MSTRETCH, which is issued by choosing Multiple Entity Stretch, enables you to select the objects to be stretched with more than one crossing window or polygon. This command is designed to use only a crossing window (the default option) or a crossing polygon to select the objects. Another difference between STRETCH and MSTRETCH is that MSTRETCH does not offer a displacement option; you must specify two points to define the distance and the direction of the stretch.

Move Copy Rotate

You have the grip commands Move and Rotate, and by using the Copy option, you also can make copies with grips. If you need more flexibility in selecting the objects to edit, you can use the MOVE, COPY, and ROTATE commands. The MOCORO command, which is issued by choosing Move Copy Rotate, enables you to perform all three editing operations on the selected objects. After selecting the objects you want to edit, you are prompted to select a base point. This base point is the base point that is used in the Move, Copy, and Rotate operations. After picking a base point, the following prompt is displayed:

Move/Copy/Rotate/Scale/Base pt/Undo/<eXit>:

Choose the option corresponding to the operation you want to carry out. After the selected operation is carried out, the Command: prompt is re-displayed, enabling you to choose another option. To exit the command, choose the default option, eXit.

Cookie Cutter Trim

To issue the EXTRIM command, choose Cookie Cutter Trim. This command is different from the TRIM command in that you need not select the objects to be trimmed. Instead, you simply select the object (a line, circle, arc, or polyline) to be used as the cutting edge when EXTRIM prompts you to do so. Thereafter, all you have to do is pick a point to indicate on which side of the cutting edge you want to trim. EXTRIM then automatically trims the objects that intersect with the cutting edge, removing the portion that resides on the side of the cutting edge you indicated with your pick point.

EXTRIM is especially useful when you have a closed or almost closed cutting edge defined (such as a circle or a closed polyline). In such situations, the point you pick to indicate which side of the cutting edge to trim really indicates whether you want the portions outside or inside the cutting edge trimmed. In the example shown in figure 11.11, the circle is used as the cutting edge. When you pick inside the circle 1 as the side of the cutting edge to trim, you get result A. When you pick outside the circle 2 as the side of the cutting edge to trim, you get result B.

Figure 11.11 When you use EXTRIM with a closed cutting edge, of the edge to trim, you can specify which side of the edge to trim.

Extended XCLIP

CLIPIT is issued by choosing Extended Xclip. Generally, you use IMAGECLIP to clip an image and XCLIP to clip an external reference or block insertion.

With both the IMAGECLIP and the XCLIP commands, the clipping boundary is restricted to a rectangular area or an irregular area defined by a polyline comprising line segments (no arc segments). CLIPIT combines IMAGECLIP and XCLIP into one command, enabling you to clip an external reference, a block insertion, or an image. Additionally, CLIPIT enables you to define the clip boundary with an arc or a circle.

NOTE: Blocks are covered in Chapter 12, "Creating and Using Blocks," and in Chapter 13, "External References."

Actually, CLIPIT approximates the shape of the arc or circle with a polyline that consists of a finite number of segments (see fig. 11.12). The number of segments is set when you enter a value in response to the prompt Resolution for segmentation of arcs (large val = smooth):. The higher the number, the more segments used to approximate the curve.

Figure 11.12 Approximating a curve with a polyline.

TIP: If you simply press Enter, instead of typing a number for the resolution, CLIPIT uses a number based on the resolution of your display. This default number usually is adequate for acceptable results.

CLIPIT simply invokes the clipping option for images, blocks, and external references. This command does not change the object in any way. To restore the unclipped display of the object, you must use the Off option in either IMAGECLIP or XCLIP, whichever is appropriate.

Multiple PEDIT

MPEDIT is issued by choosing Multiple Pedit. The difference between MPEDIT and PEDIT is that with MPEDIT, you can affect more than one polyline at a time for certain options. With MPEDIT, you can perform the following actions:

The major omission in MPEDIT (compared to PEDIT) is the Vertex option, which enables you to edit, add, or delete specific vertex points. If you want to edit the vertex points of a polyline, use grips or the PEDIT command. For a thorough coverage of PEDIT, see Chapter 8, "Creating Polylines and Splines."

Trim to Block Entities

You cannot use the standard TRIM command to trim objects to component objects of an insertion of a block. The bonus command TRMBLK, which is issued by choosing Trim to Block Entities, enables you to select certain types of objects within an insertion of a block, as the cutting objects for the TRIM command. As with the EXTBLK command, some limitations exist as to the types of component objects of an insertion that you can select to use as cutting edges. If you are dealing with a uniformly scaled block insertion (X, Y, and Z scales are equal), you only can select lines, circles, arcs, text, and mtext objects. With non-uniformly scaled block insertions, you only can select lines. Unlike the TRIM command, TRMBLK does not have the Edge or Project options.

Extend to Block Entities

You cannot use the standard EXTEND command to extend objects to component objects of an insertion of a block. The bonus command EXTBLK, which is issued by choosing Extend to Block Entities, enables you to select certain types of objects within an insertion of a block, as the boundary objects for the EXTEND command. There are, however, some limitations as to the types of component objects of an insertion that you can select to use as boundary objects. If you are dealing with a uniformly scaled block insertion (X, Y, and Z scales are equal), you only can select lines, circles, arcs, text, and mtext objects. With non-uniformly scaled block insertions, you only can select lines. Unlike the EXTEND command, EXTBLK does not have the Edge or Project options.

Modifying Specific Types of Objects

Some objects have an associated editing command to enable you to perform certain modifications to that specific type of object. This section covers these object-specific editing commands, which are issued from the Objects submenu of the Modify pull-down menu. To fully understand how or when each editing command is used, you might need to read the chapter in which the specific object type is covered in detail.

Editing a Hatch

The HATCHEDIT command enables you to modify the parameters of an associative hatch object. Choosing Hatch from the Objects submenu issues the HATCHEDIT command and displays the Hatchedit dialog box (see fig. 11.13).

Figure 11.13 The dialog box of HATCHEDIT.

Using the Hatchedit dialog box, you can change the pattern or any of the other parameters that govern the generation of the hatch. You can even remove the associativity or even explode the hatch object (though neither is recommended). Drawing and editing hatch objects are covered in detail in Chapter 17, "Drawing Hatch Patterns."

In the following exercise, you use some of the bonus commands to complete the landscaping design for a building.

EDITING LANDSCAPE WITH THE BONUS COMMANDS

1. Open the drawing LANDSCAPE.DWG found in the Chapter 11 Exercise folder of the accompanying CD. Choose Named Views from the View menu. Restore the view ENTRANCE.

2. Choose Cookie Cutter Trim from the Modify submenu of the Bonus menu. Pick 1 (see fig. 11.14) to select the rectangular polyline as the cutting edge. Pick 2 as the side to trim on. All the lines are then trimmed back to the polyline (see fig. 11.15).

Figure 11.14 The pick points needed for the various bonus commands to trim lines, make copies, and stretch objects.

3. Choose Named Views from the View menu. Restore the view FRONT-LAWN. Choose Move Copy Rotate from the Modify submenu of the Bonus menu. Pick 3 to select the tree as the object to be edited. The tree is a block insertion and as such, is a single object, not a collection of lines. You will learn about blocks in Chapter 12. Press the Enter key to end the selection process. Right-click and choose Intersection and pick the center of the tree as the base point.

4. Specify the Copy option and pick 4 as the second point of displacement. Pick 5 as the second point of displacement to make a second copy. Press the Enter key to exit the Copy option.

5. Specify the Scale option. Enlarge the tree to approximately twice its original size by dragging its shape. Figure 11.15 shows what the trees should look like. Press the Enter key to end the command.

6. Choose Named Views from the View menu and restore the view ALL. Choose Multiple Entity Stretch from the Modify submenu of the Bonus menu.

7. Pick 6 and 7 to define the first crossing window. Pick 8 and 9 to define the second crossing window. Press the Enter key to end the selection process.

8. Right-click and choose Intersection. Pick 0 to select the endpoint of the line. Type @90<90 to define the second point of the stretch. Figure 11.15 shows the end result of the Multiple Entity Stretch command.

9. Save the drawing. You are done editing the drawing so you may exit the drawing.

Figure 11.15 The results of applying the Cookie Cutter Trim, Move Copy Rotate, and Multiple Entity Stretch commands.

Editing Attribute Values

There are two editing commands available that are to be used specifically on attribute objects within an insertion of a block. The commands are DDATTE and ATTEDIT, both of which are discussed in the following sections.

Using DDATTE on Attributes

If you want to change the text values of variable attributes that are part of an inserted block, use the DDATTE command, which is issued by choosing Single from the Attribute submenu. After selecting the block insertion, the Edit Attributes dialog box is displayed. It shows the attribute prompts and the current text values of the attributes (see fig. 11.16).

Figure 11.16 The Edit Attributes dialog box is displayed by the DDATTE command.

If more attributes exist than can be displayed in the dialog box, use the Next and Previous buttons to display the additional sets of attributes.

Using ATTEDIT on Attributes

Whereas DDATTE enables you to change the text values of attributes, the ATTEDIT command enables you to change other properties of inserted attributes. ATTEDIT is issued by selecting Global from the Attribute submenu. You are asked whether you want to edit attributes one at a time. If you answer No, you can perform a text search-and-replace on the selected attributes. If you answer Yes to editing attributes one at a time, you can change the value, position, height, rotation angle, style, and color of the selected attributes.

Whether you answer Yes or No, you also have the option of filtering the selected attributes by block name, attribute tag name, or attribute value. The default value for all three filters is an asterisk (*), which indicates that no filters should be used and that the attributes the user selects are to be accepted.

If you are not familiar with attributes, see Chapter 12, "Creating and Using Blocks," for complete coverage of attributes and their use in block insertions.

Editing External References

There are two editing commands available that are to be used specifically on external references. The commands are XBIND and XCLIP, both of which are discussed in the following sections.

Binding External References

To import or bind a block, dimension style, layer, linetype, or text style defined in an external reference, use the XBIND command. XBIND is issued by choosing Bind from the External Reference submenu. The Xbind dialog box (see fig. 11.17) displays all external references and the objects that can be imported from each external reference.

To clip (or hide) a portion of an inserted block or external reference, issue the XCLIP command by choosing Clip from the Object submenu. With XCLIP, you define a rectangular or irregular polyline clipping boundary for the selected block insertion or external reference. The portion of the block insertion and external reference outside the clipping boundary then becomes invisible. XCLIP also enables you to turn clipping on or off, or display or delete the clipping boundary of the selected object. One option, Clipdepth, is designed for use in 3D drawings.

Figure 11.17 A typical Xbind dialog box displays the external references and the objects that can be imported from them.

You can display the clipping boundaries of all block insertions and external references by turning on the system variable XCLIPFRAME. XCLIPFRAME is accessed by choosing Frame from the External Reference submenu.

For additional information about blocks and external references, see Chapters 12 and 13, respectively.

Editing Images

There are three editing commands available that are to be used specifically on images. The commands are IMAGECLIP, IMAGEADJUST, and TRANSPARENCY. In addition to the commands, the system variables IMAGEFRAME and IMAGEQUALITY affects images. The commands and system variable are discussed in the following sections.

Clipping Images

You can clip portions of an image also. The equivalent of XCLIP for images is IMAGECLIP, which is issued by choosing Image Clip from the Object submenu. With IMAGECLIP, you define a new rectangular or irregular polyline clipping boundary, or turn on or off the clipping boundary, to delete the clipping boundary. To display the clipping frame of all images, turn on the system variable IMAGEFRAME by choosing Frame from the Image submenu.

Adjusting the Image

Several additional editing commands are available in the Image submenu. Choosing Adjust issues the IMAGEADJUST command and displays the Image Adjust dialog box (see fig. 11.18), in which you can adjust the brightness, contrast, and fade settings of the selected image.

Figure 11.18 The Image Adjust dialog box is displayed by the IMAGEADJUST command.

You can accelerate the display of images by setting the system variable IMAGEQUALITY to the Draft setting. IMAGEQUALITY, accessed by choosing Quality from the Image submenu, affects only the display of images, not the plotting of images; images are always plotted at the High quality setting.

Controlling Transparency

Some image file formats support a transparency setting for pixels. When transparency is enabled, the graphics on the display show through the transparent pixels of the overlaid image. By default, images are inserted with transparency off. You can turn this setting on or off for the selected images by using the TRANSPARENCY command, issued by choosing Transparency from the Image submenu.

Editing Multilines

The MLEDIT command is designed specifically to enable you to perform specialized editing operations on mline objects. To issue the MLEDIT command, choose Multiline from the Objects submenu. Figure 11.19 shows the Multiline Edit Tools dialog box.

Figure 11.19 The Multiline Edit Tools dialog box is displayed by the MLEDIT command.

With MLEDIT, you can clean up various types of intersections of two mlines, remove or add a vertex point in an mline, and insert or heal breaks in an mline. Mlines are covered in detail in Chapter 9, "Creating Complex Objects."

Editing Polylines

PEDIT is designed for polylines and is issued by choosing Polyline from the Object submenu. With PEDIT, you can accomplish the following tasks:

Polylines are covered in detail in Chapter 8, "Creating Polylines and Splines."

Editing Splines

SPLINEDIT is designed for splines and is issued by choosing Spline from the Objects submenu. With SPLINEDIT, you can accomplish the following tasks:

Splines are covered in detail in Chapter 8, "Creating Polylines and Splines."

Editing Text and Mtext

DDEDIT, designed to edit text and mtext objects, is issued by choosing Text from the Objects submenu. If a text object is selected, a line text editor is displayed. If an mtext object is selected, the Multiline Text Editor dialog box is displayed. The drawing and editing of text is covered in detail in Chapter 16, "Text Annotation."

Summary

This completes the discussion of the general editing commands available to you. This chapter also introduced you to the available object-specific editing commands. To learn more about how and when to create and edit the objects discussed with the object-specific editing commands, please refer to the chapters cited in the text. In the next chapter, you learn how to create and use blocks, an important productivity tool.

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