Drawing Straight Lines

The basic object in AutoCAD is the line. If you worked through the exercises in earlier chapters, you've already used lines. Drawing lines consists of four basic steps:

1. Click the Line tool in the 2D Draw control panel, or enter L↲ at the command prompt.

2. Click a start point, or enter a coordinate.

3. Continue to select points, either by clicking them or by entering coordinates, to place a series of contiguous line segments.

4. Press ↲ to exit the Line command, or enter C↲ to join the last line endpoint with the first.

When you draw a series of contiguous line segments using the Line command, each line segment behaves like an individual object. You can move the segments separately or change their individual properties.

You typically don't just draw a line and leave it alone. Lines tend to get edited a lot. Some of the most commonly used editing commands for lines are Trim, Extend, Fillet, and Offset. Trim and Extend either trim lines to intersecting lines or extend lines to other objects. Fillet joins two lines exactly end to end or adds an arc between them. And Offset makes a parallel copy of a line at a specific distance.

As useful as lines are, you might find that you need your contiguous line segments to behave as a single object instead of as a series of individual lines. Another type of object called a polyline is just such an object. Using the Polyline command, you can draw a series of line segments, and they will behave as a single object. In fact, the rectangle is really a polyline that is closed. So are regular polygons created by the Polygon command, described later.

To draw lines with the Polyline command, click the Polyline tool in the 2D Draw control panel, or choose Draw è Polyline. Then start selecting points, just as you would with the Line command. Press ↲ when you finish drawing your lines.

When you click a polyline, instead of just selecting a line segment, you select the entire polyline. You can "break down" a polyline into its constituent parts by using the Explode command. (See Chapter 4 for more about Explode.)

Polylines can help you construct some types of objects quickly. Figure 3.1 shows some examples of polylines that have been created from standard AutoCAD commands or edited to form complex shapes.

Figure 3.1: Although different commands were used to create them, these objects are all polylines and can be edited as such.