First, to learn about the polyline, you'll begin a drawing of the top view of the joint shown in Figure 19.1.

Figure 19.1. A sketch of a metal joint

Follow these steps to draw the joint:

You now have a sideways, U-shaped polyline that you'll use in the next exercise to complete the top view of your joint.

Let's take a break from the tutorial to look at some of the options in the Polyline prompt that you didn't use:

If you want to break a polyline into simple lines and arcs, you can use the Explode option on the Modify panel, just as you would with blocks. After a polyline is exploded, it becomes a set of individual line segments or arcs.

To turn off the filling of solid polylines, open the Options dialog box and click the Display tab. Clear the Apply Solid Fill check box in the Display Performance group.

Filleting a Polyline

You can use the Fillet tool on the Modify panel to fillet all the vertices of a polyline composed of straight-line segments. Click the Fillet tool, set your fillet radius by typing R

Here's a brief look at a few of the Pedit options you didn't try firsthand:

You can create a curve in AutoCAD in many ways. If you don't need the representation of a curve to be accurate, you can use a polyline curve. In the following exercise, you'll draw a polyline curve to represent a contour on a topographical map:

Your contour is now complete. The Fit option under the Pedit command causes AutoCAD to convert the straight-line segments of the polyline into arcs. The endpoints of the arcs pass through the endpoints of the line segments, and the curve of each arc depends on the direction of the adjacent arc. This gives the effect of a smooth curve. Next you'll use this polyline curve to experiment with some of the editing options unique to the Pedit command.

Figure 19.9. The topo.dwg file shows survey data portrayed in an AutoCAD drawing. Notice the dots indicating where elevations were taken. The actual elevation value is shown with a diagonal line from the point.

Turning Objects into Polylines and Polylines into Splines

At times, you'll want to convert regular lines, arcs, or even circles into polylines. You might want to change the width of lines or join lines to form a single object such as a boundary. Here are the steps to convert lines, arcs, and circles into polylines:

1. Click the Edit Polyline tool from the Home tab's expanded Modify panel, or type Pe

   

2. At the Select polyline or [Multiple]: prompt, pick the object you want to convert. If you want to convert a circle to a polyline, first break the circle (using the Break option on the Modify panel), so it becomes an arc of approximately 359°.

3. At the prompt

   Object selected is not a polyline. Do you want to turn it into one? <Y>:

   press

   

If you want to convert several objects to polylines, type M

To turn a polyline into a true spline curve, do the following:

1. Click the Edit Polyline tool from the Home tab's expanded Modify panel, or type Pe

   

2. Type S

   

3. Click the Spline tool on the Home tab's expanded Draw panel. Type Spl

   

4. At the Specify first point or [Object]: prompt, type O

   

5. At the Select objects: prompt, click the polyline spline. Although it may not be apparent at first, the polyline is converted into a true spline.

You can also use the Edit Spline tool on the Home tab's expanded Modify panel (or enter Spe

If you know you'll always want to convert an object into a polyline when using Pedit, you can turn on the Peditaccept system variable. Enter peditaccept

One of the Pedit options that I haven't yet discussed, Edit Vertex, is like a command within a command. Edit Vertex has numerous suboptions that enable you to fine-tune your polyline by giving you control over individual vertices.

To access the Edit Vertex options, follow these steps:

When using Edit Vertex, you must be careful about selecting the correct vertex to be edited. Edit Vertex has six options. You often have to exit the Edit Vertex operation and use Pedit's Fit option to see the effect of several Edit Vertex options on a curved polyline.

Edit Vertex Suboptions

After you enter the Edit Vertex mode of the Pedit command, you can perform the following functions:

• Break the polyline between two vertices.

• Insert a new vertex.

• Move an existing vertex.

• Regen the drawing to view the current shape of the polyline.

• Straighten a polyline between two vertices.

• Change the tangential direction of a vertex.

• Change the width of the polyline at a vertex.

These functions are presented in the form of the following prompt:

[Next/Previous/Break/Insert/Move/Regen/Straighten/Tangent/Width/eXit] <N>:

The following sections examine each of the options in this prompt, starting with Next and Previous.

The Next and Previous Options

The Next and Previous options let you select a vertex for editing. When you start the Edit Vertex option, an X appears on the selected polyline to designate its beginning. As you select Next or Previous, the X moves from vertex to vertex to show which one is being edited. Let's try this:

1. Press

   

2. Type P

   

Real World Scenario: Controlling A Polyline Or Spline Direction

One of more frequently asked questions I receive from readers is "How can I reverse the direction of a polyline?" It may seem like an odd question to someone new to AutoCAD, but reversing a polyline has quite a few uses. Perhaps the most common use is to turn a polyline that uses a complex linetype, one that includes text, right side up so that the text can be read more easily. (See Chapter 28 for an example of a linetype that includes text.) If for some reason you need to reverse the direction of a polyline or spline, you can do so by using the Reverse tool. You can find the Reverse tool on the Home tab's expanded Modify panel.

The Break Option

The Break option breaks the polyline between two vertices:

1. Position the X on one end of the segment you want to break.

2. Enter B

   

3. At the Enter an option [Next/Previous/Go/eXit] <N>: prompt, use Next or Previous to move the X to the other end of the segment to be broken.

4. When the X is in the proper position, enter G

   

Figure 19.10. How the Break option works

You can also use the Break and Trim options on the Modify panel to break a polyline anywhere, as you did when you drew the toilet seat in Chapter 3.

The Insert Option

Next, try the Insert option, which inserts a new vertex:

1. Type X

   

2. Type E

   

3. Press

   

4. Enter I

   

5. When the prompt Specify location for new vertex: appears, along with a rubber-banding line originating from the current X position (see Figure 19.11), pick a point indicating the new vertex location. The polyline is redrawn with the new vertex.

Figure 19.11. The new vertex location

Notice that the inserted vertex appears between the currently marked vertex and the next vertex, so the Insert option is sensitive to the direction of the polyline. If the polyline is curved, the new vertex won't immediately be shown as curved. (See the first image in Figure 19.12.) You must smooth it out by exiting the Edit Vertex option and then using the Fit option, as you did to edit the site plan. (See the second image in Figure 19.12.) You can also use the Stretch command (on the Modify panel) to move a polyline vertex.

Figure 19.12. The polyline before and after the curve is fitted

The Move Option

In this brief exercise, you'll use the Move option to move a vertex:

1. Undo the inserted vertex by exiting the Edit Vertex option (enter X

   

2. Restart the Edit Vertex option, and use the Next or Previous option to place the X on the vertex you want to move.

3. Enter M

   

4. When the Specify new location for marked vertex: prompt appears, along with a rubber-banding line originating from the X (see the first image in Figure 19.13), pick the new vertex. The polyline is redrawn (see the second image in Figure 19.13). Again, if the line is curved, the new vertex appears as a sharp angle until you use the Fit option (see the final image in Figure 19.13).

Figure 19.13. Picking a new location for a vertex with the polyline before and after the curve is fitted

You can also move a polyline vertex by using its grip.

The Regen Option

In some cases, the effect of an option does not appear in the drawing immediately. You can use the Regen option to update the display of the polyline and see any changes you've made up to that point.

The Straighten Option

The Straighten option straightens all the vertices between two selected vertices. Using the Straighten option is a quick way to delete vertices from a polyline, as shown in the following exercise:

1. Undo the moved vertex (from the previous exercise).

2. Start the Edit Vertex option again, and select the starting vertex for the straight line.

3. Enter S

   

4. At the Enter an option [Next/Previous/Go/eXit] <N>: prompt, move the X to the location for the other end of the straight-line segment.

5. After the X is in the proper position, enter G

   

Figure 19.14. A polyline after straightening

The Tangent Option

The Tangent option alters the direction of a curve on a curve-fitted polyline:

1. Undo the straightened segment from the previous exercise.

2. Restart the Edit Vertex option, and position the X on the vertex you want to alter.

3. Enter T

   

4. Point the rubber-banding line in the direction of the new tangent, and click the mouse. An arrow appears, indicating the new tangent direction. (See the second image in Figure 19.15.)

Figure 19.15. Picking a new tangent direction

Don't worry if the polyline shape doesn't change. You must use Fit to see the effect of Tangent. (See the final image in Figure 19.15.)

The Width Option

Finally, you'll try the Width option. Unlike the Pedit command's Width option, the Edit Vertex/Width option enables you to alter the width of the polyline at any vertex. Thus you can taper or otherwise vary polyline thicknesses. Try these steps:

1. Undo the tangent arc from the previous exercise.

2. Return to the Edit Vertex option, and place the X at the beginning vertex of a polyline segment you want to change.

3. Type W

   

4. At the Specify starting width for next segment <0.0000>: prompt, enter a value—12, for example—indicating the polyline width desired at this vertex.

5. At the Specify ending width for next segment <12.0000>: prompt, enter the width—24, for example—for the next vertex.

The width of the polyline changes to your specifications (see Figure 19.16).

Figure 19.16. A polyline with the width of one segment increased

The Width option is useful when you want to create an irregular or curved area in your drawing that is to be filled in solid. This is another option that is sensitive to the polyline direction.

As you've seen throughout these exercises, you can use the Undo option to reverse the last Edit Vertex option used. You can also use the Exit option to leave Edit Vertex at any time. Enter X

Enter an option [Close/Join/Width/Edit vertex/Fit/Spline/Decurve/Ltypegen/Undo]:

Filling In Solid Areas

You've learned how to create a solid area by increasing the width of a polyline segment. But suppose you want to create a solid shape or a thick line. AutoCAD provides the Solid, Trace, and Donut commands to help you draw simple filled areas. The Trace command acts just like the Line command (with the added feature of allowing you to draw wide line segments). Trace lets you create solid filled areas with straight sides, and Donut draws circles with a solid width.

You can create free-form, solid-filled areas by using the solid hatch pattern. Create an enclosed area by using any set of objects, and then use the Hatch tool to apply a solid hatch pattern to the area. See Chapter 7 for details on using the Hatch tool.

To create a spline curve, follow the steps described here. You don't have to do them now. Make a note of this section, and refer to it when you need to draw and edit a spline:

Figure 19.20. Starting the spline curve at the first data point

Figure 19.21. The last two prompts of the Spline command let you determine the tangent direction of the spline.

You now have a smooth curve that passes through the points you selected. These points are called the control points. If you click the curve, you'll see the grips appear at the location of these control points, and you can adjust the curve by clicking the grip points and moving them. (You may need to turn off the Data layer to see the grips clearly.)

You may have noticed two other options—Fit Tolerance and Close—as you were selecting points for the spline in the previous exercise. Here is a description of these options:

Spline curves are different from other types of objects, and many of the standard editing commands won't work on splines. AutoCAD offers the Edit Spline option, otherwise known as the Splinedit command, in the Home tab's expanded Modify panel for making changes to splines.

Controlling the Fit Data of a Spline

The Fit Data option of the Splinedit command lets you adjust the tangency of the beginning and endpoints, add new control points, and adjust spline tolerance settings. To get to these options, follow these steps:

1. 

2. At the Select spline: prompt, select the spline you drew in the previous exercise.

3. At the Enter an option [Fit data/Close/Move vertex/Refine/rEverse/Undo]: prompt, type F

   

4. At the [Add/Close/Delete/Move/Purge/Tangents/toLerance/eXit] <eXit>: prompt, enter the option you want to use. For example, to change the tangency of the first and last points of your spline, type t

   

The Refine option of the Splinedit command lets you control the pull exerted on a spline by an individual control point.

If you prefer, you can double-click on a spline to start the Splinedit command instead of selecting the Edit Spline tool in the Modify panel. If you have the Dynamic Input feature turned on, you can select Splinedit options from a menu that appears at the cursor (Figure 19.22) instead of typing in the option keyboard shortcuts.

Table 19.1. The Fit Data Options of the Splinedit Command

Option	Function
Add	Lets you add more control points
Close	Lets you close the spline into a loop
Delete	Removes a control point from the spline
Move	Lets you move a control point
Purge	Deletes the fit data of the spline, thereby eliminating the Fit Data option for the purged spline
Tangents	Lets you change the tangency of the first and last points
toLerance	Controls the distance between the spline and a control point

Figure 19.22. The Splinedit options

When Can't You Use Fit Data?

The Fit Data option of the Splinedit command offers many ways to edit a spline. However, this option isn't available to all spline curves. When you invoke certain other Splinedit options, a spline curve loses its fit data, thereby disabling the Fit Data option. These operations are as follows:

• Fitting a spline to a tolerance (Spline/Fit Tolerance) and moving its control vertices.

• Fitting a spline to a tolerance (Spline/Fit Tolerance) and opening or closing it.

• Refining the spline.

• Purging the spline of its fit data by using the Purge option of the Splinedit command. (Choose Edit Spline from the expanded Modify panel, or enter Splinedit

  

Also note that the Fit Data option isn't available when you edit spline curves that were created from polyline splines. See the sidebar "Turning Objects into Polylines and Polylines into Splines" earlier in this chapter.

If you'd like to learn more about the Splinedit options, check the AutoCAD Help window. It offers a detailed description of how these options work.

Convert a Spline into a Polyline

AutoCAD 2010 now allows you to convert a spline object into a polyline. This can be very useful when you want to edit a spline using the polyline edit tools instead of the spline editing tools. You will lose some precision in the conversion, but more often than not, this is not an issue.

To convert a spline to a polyline, double-click the spline, and then at the Enter and option prompt, type P

Use the Divide command to divide an object into a specific number of equal segments. For example, suppose you need to mark off the contour you've been working on in this chapter into nine equal segments. One way to do this is to first find the length of the contour by using the List command and then sit down with a pencil and paper to figure out the exact distances between the marks. But there is another, easier way.

The Divide command places a set of point objects on a line, an arc, a circle, or a polyline, marking off exact divisions. The following exercise shows how it works:

Figure 19.25. The Point Style dialog box

You can also change the point style by changing the Pdmode system variable. When Pdmode is set to 3, the point appears as an X.

The Divide command uses point objects to indicate the division points. You create point objects by using the Point command. They usually appear as dots. Unfortunately, such points are nearly invisible when placed on top of other objects. But, as you've seen, you can alter their shape by using the Point Style dialog box. You can use these X points to place objects or references to break the object being divided. (The Divide command doesn't cut the object into smaller divisions.)

Sketching With AutoCAD

AutoCAD offers the Sketch command, which lets you do freehand drawing. The Sketch command can be set to draw polylines. If you'd like to know more about Sketch, the AutoCAD Help window offers an excellent description of how it works. Press the F1 function key, open the Contents tab, and then expand the Command Reference listing to Command

The Measure command acts just like Divide. However, instead of dividing an object into segments of equal length, the Measure command marks intervals of a specified distance along an object. For example, suppose you need to mark some segments exactly 5″ apart along the contour. Try the following exercise to see how the Measure command is used to accomplish this task:

Bear in mind that the point you pick on the object to be measured determines where the Measure command begins measuring. In the previous exercise, for example, you picked the contour near its bottom endpoint. If you picked the top of the contour, the results would be different because the measurement would start at the top, not the bottom.