Using Objects to Lay Out Your Drawing

Often when you are sketching with pencil and paper, you draw some lines to help lay out your sketch. You can do the same in AutoCAD using any object. But AutoCAD also provides a few tools specifically designed to help you lay out your drawing.

You can use Divide and Measure to mark off an object at regular intervals. If you are familiar with manual drafting tools, you can think of Measure as analogous to a divider. Measure marks off exact distances along an object. The Divide command is similar to Measure, but instead of marking off a known distance you specify, it marks divisions of an object to exact, equal segments. For example, if you want to mark off a line of unknown length into 12 equal divisions, you use the Divide command.

You can use point objects to mark exact points in a drawing. In fact, the Divide and Measure commands use points as markers. Point objects can be helpful in surveying to mark off datum locations or waypoints, for example.

Ray and Xline are two commands that create lines with special characteristics. Ray creates a line that starts at a selected point and extends into an infinite distance much like the rays of light from the sun. Xline creates a line that has an infinite length in both directions. Unlike rays, xlines do not have a beginning point. You specify a point through which the xline passes and a direction.

Marking Points in a Drawing

Point objects are AutoCAD objects that are commonly used to mark an exact point in a drawing. Point objects are used as markers by commands that mark off equal divisions on objects. You can also create point objects by using the Point command. To place a point in a drawing, choose Draw è Point è Single Point, or choose Draw è Point è Multiple Points.

Point objects can be difficult to see. Fortunately, you can alter their appearance to make them more visible. To see point objects more clearly, follow these steps:

1. Choose Format è Point Style to open the Point Style dialog box.

   

2. Click the x point style in the upper-right of the dialog box, click the Set Size Relative To Screen button, and then click OK.

3. If you have already used the Divide or Measure command or have placed points in your drawing, choose View è Regen, or enter Re↲. The point objects in the drawing change into x's, as shown in Figure 3.22.

   You can change the point style any time, and all the points in a drawing will change to the new style.

Figure 3.22: An example of point objects, appearing as X's, used to mark divisions on a polyline

If you are using point objects as visual markers only and do not want them to print, you can put them on a layer you create specifically for point objects and then set that layer as a nonprinting layer. See Chapter 7 for more about layers.

Marking Off Equal Divisions

You can use the Divide command to divide an object into a specific number of equal segments. The Divide command places a set of point objects on a line, an arc, a circle, a spline, or a polyline, marking off exact divisions. This exercise shows how it works:

1. Choose Draw è Point è Divide, or enter Div↲.

2. At the Select object to divide: prompt, select the object you want to mark off.

3. The Enter number of segments or [Block]: prompt that appears next asks you for the number of divisions you want on the selected object. Enter the number of divisions you want.

The command prompt now returns, and it might appear that nothing has happened. AutoCAD has placed several point objects on the selected object. These point objects indicate the locations of the divisions you requested. They do not actually cut the object. They just mark the object. You can use the Node osnap to select a point exactly at the point objects' locations.

Dividing Objects into Specified Lengths

The Measure command acts just like Divide; however, instead of dividing an object into equal-length segments, the Measure command marks intervals of a specified distance along an object. For example, suppose you need to mark off segments exactly 4 units long along a curve (see Figure 3.23).

Figure 3.23: Marking off 4-unit segments on a curve

The following steps describe how you use the Measure command to accomplish this task:

1. Choose Draw è Point è Measure, or enter Me↲.

2. At the Select object to measure: prompt, click the object closest to the end from which you want the measured divisions to start.

3. At the Specify length of segment or [Block]: prompt, enter the length you want. The point objects appear at the specified distance.

Using Construction Lines

Many graphics programs include an alignment guide, which is usually a nonprinting line that can be dragged into the work area. AutoCAD offers a similar function in the construction line, otherwise known as the Xline command.

Unlike the alignment guide of other programs, AutoCAD's construction line prints. You can also edit construction lines so that they become a standard line in the AutoCAD drawing, place them with accuracy, and rotate them to any angle you like.

MARKING OFF INTERVALS USING DRAWING ASSEMBLIES INSTEAD OF POINT OBJECTS

Marking off regular distances isn't the only use for the Divide and Measure commands. You can also place drawing assemblies, such as symbols or parts, at regular intervals along an object. For example, you can use the Block option of Divide or Measure to place a row of sinks equally spaced along a wall or place a row of parking spaces along a curb.

To replace the point objects with assemblies, you use the Block option in the Divide or Measure command. Blocks are an assembly of objects that form an image that can be readily copied, like a rubber stamp. (See Chapter 8 for more about blocks.) The blocks take the place of the point objects as markers.

Here's how to use blocks as markers:

1. Be sure the block you want to use is part of the current drawing file.

2. Start either the Divide command or the Measure command.

3. At the Specify length of segment or [Block]: prompt (or Specify number of segments or [Block]: prompt for the Divide command), enter B↲.

4. At the Enter name of block to insert: prompt, enter the name of a block.

5. At the Align block with object? [Yes/No] <Y>: prompt, press ↲ if you want the blocks to follow the alignment of the selected object. (Entering N↲ inserts each block at a 0° angle.)

6. At the Enter the number of Segments: prompt, enter the number of segments. The blocks appear at regular intervals on the selected object.

The block's insertion point is placed on the divided or measured object in the location where the point object would usually be placed.

Drawing Multiple Construction Lines through a Point

To draw multiple construction lines through a point, follow these steps:

1. Click the Construction Line tool in the 2D Draw control panel, choose Draw è Construction Line, or enter Xline↲ at the command prompt.

2. At the Specify a point or [Hor/Ver/Ang/Bisect/Offset]: prompt, select a point through which the construction line is to pass. If you don't have an exact location, you can always move the construction line later.

3. At the Specify through point: prompt, you'll see a temporary construction line that passes through the point you selected in step 2 and follows the cursor. Select another point to indicate the angle for the construction line.

4. You can continue to select points to draw several construction lines through the first point you selected in step 2.

5. Press ↲ to exit the Construction Line tool.

Once you have a construction line in the drawing, you can move, copy, and edit the line as you would other lines.

Drawing Multiple Horizontal, Vertical, or Angled Construction Lines

Using the default method shown in the previous exercise, you can draw multiple construction lines passing through the same point. But what if you want to draw multiple lines that are all vertical or horizontal or all even at an angle? The Construction Line tool offers several options that allow you to add multiple horizontal or vertical lines as well as lines at a specified angle. Here's how these options work:

1. Click the Construction Line tool in the 2D Draw control panel, choose Draw è Construction Line, or enter Xline↲ at the command prompt.

2. At the Specify a point or [Hor/Ver/Ang/Bisect/Offset]: prompt, enter H↲ for multiple horizontal lines or V↲ for multiple vertical lines.

3. Select points in the drawing to place your construction lines.

4. Press ↲ to exit the Construction Line tool.

For multiple construction lines at the same angle, do the following:

1. Click the Construction Line tool in the 2D Draw control panel, choose Draw è Construction Line, or enter Xline↲ at the command prompt.

2. At the Specify a point or [Hor/Ver/Ang/Bisect/Offset]: prompt, enter A↲, and then enter the angle for the lines you want to place in the drawing.

3. Select points in the drawing to place your construction lines.

4. Press ↲ to exit the Construction Line tool.

Optionally, in step 2, you can enter A↲ R↲ and then select an existing line whose angle you want to match.

Drawing Bisecting Construction Lines

If you need to draw a line that bisects the angle between two other lines, you can do so with the Bisect option of the Construction Line tool. Here's how the Bisect option works:

1. Click the Construction Line tool in the 2D Draw control panel, choose Draw è Construction Line, or enter Xline↲ at the command prompt.

2. At the Specify a point or [Hor/Ver/Ang/Bisect/Offset]: prompt, enter B↲.

3. At the Specify angle vertex point: prompt, use the Intersection osnap, and select the intersection of the two lines you want to bisect (see Figure 3.24). See "Selecting Exact Locations on Objects" in Chapter 2 if you need a little refresher on using osnaps.

4. At the Specify angle start point: prompt, use the Nearest osnap, and select one of the pair of lines you want to bisect.

5. At the Specify angle end point: prompt, use the Nearest osnap, and select the other line. A construction line appears that bisects the pair you selected.

6. You can continue placing bisecting construction lines, or you can press ↲ to exit the command.

Figure 3.24: Bisecting a pair of lines with a construction line

Creating Construction Lines Parallel to Existing Lines

The last option of the Construction Line tool lets you create a construction line that is parallel to an existing line. This option works just like the Offset command described earlier in this chapter, but instead of creating a copy of an object, the Offset option creates a straight construction line. Here's how:

1. Click the Construction Line tool in the 2D Draw control panel, choose Draw è Construction Line, or enter Xline↲ at the command prompt.

2. At the Specify a point or [Hor/Ver/Ang/Bisect/Offset]: prompt, enter O↲.

3. At the Specify offset distance or [Through] <Through>: prompt, indicate a distance by either entering a distance through the keyboard or selecting two points in the drawing area. You can use osnaps to indicate distances based on existing objects in the drawing.

4. At the Select a line object: prompt, select the object to which you want to create the construction line parallel.

5. At the Specify side to offset: prompt, select the side of the object where you want the copy to appear. AutoCAD creates a parallel construction line at the distance you specified in step 2.

6. Repeat step 4 for more parallel construction lines, or press ↲ to exit the Offset command.

Placing Ray Construction Lines

The construction line is unusual in that it has no endpoint. It extends into a virtual infinity in two directions. If you want a construction line that has a starting point, you can use a ray. A ray can be useful when editing circular objects because they can be easily rotated about an origin point. Here's how to place a ray in a drawing:

1. Choose Draw è Ray from the menu bar, or enter ray↲ at the command prompt.

2. At the Specify start point: prompt, select a point for the beginning of the ray.

3. At the Specify through point: prompt, select another point to indicate the direction of the ray.

4. Continue to place more rays by selecting points, or press ↲ to exit the command.

OTHER DRAWING METHODS

You create most 2D drawings in AutoCAD using the commands presented in this chapter, but you can use two other methods: the region and freehand sketching.

The region object acts more like a paper cutout shape. Regions are always closed outlines of shapes, and you can even convert a closed polyline into a region. You can add and subtract regions to build 2D shapes using what are called Boolean operations. (See Chapter 5 for information about Boolean operations.)

To create a region, first create a closed polyline. You can use the Polyline, Rectangle, or Polygon tool to do this. Next, issue the Region command by choosing Draw è Region or by clicking the Region tool in the 2D Draw control panel. Select the closed polylines you want to convert, and then press ↲. You can add and subtract regions using the Boolean operations described in Chapter 5.

The Sketch command lets you draw freehand, though this method of drawing really doesn't make sense unless you are using a drawing tablet. Even then, the Sketch command is rarely used.

If you'd like to find out more about regions and the Sketch command, check the AutoCAD Help system. You'll also find information about these features in Mastering AutoCAD 2008 and AutoCAD LT 2008, published by Sybex.