AutoCAD For Dummies. Ralph GrabowskiЧитать онлайн книгу.

RAY: Draws a line (known as a ray) that starts at a point and extends to infinity at a specified angle away from the start point.

You use the RAY and XLine commands to draw construction lines that guide the construction of other geometry. Using construction lines is less common in AutoCAD than in certain other CAD programs and is far less common than in pencil-and-paper drawings. The many precision techniques in AutoCAD usually provide methods for creating new geometry that are more efficient than adding construction lines to a drawing. In particular, object snap tracking (discussed in Chapter 8) and parametrics (discussed in Chapter 19) usually eliminate the need for construction geometry or even for a mitre line when creating orthographic views.

Although xlines and rays are infinitely long, they don’t increase the extents of your drawing to infinity. The question of the day is, “Which is longer: an XLine that extends to infinity in both directions or a RAY that extends to infinity in one direction?”

Drawing Lines and Polylines

The Line command works well for many drawing tasks, but the PLine command works better for others. Experience can help you choose which one works best for your design needs. As the PLine command draws polylines, you often hear CAD drafters refer to polylines as a p-lines (rhymes with “bee-lines,” not to be confused with queues in busy restrooms).

Here are the primary differences between the Line and PLine commands:

The Line command draws a series of separate line segments. Even though they appear to be connected onscreen, each one is a separate object. If you move one line segment, none of the other segments you drew at the same time move with it.

The PLine command draws a single, connected, multisegmented object. A polyline is what a line appears to be; each segment is connected with the others to form a single object. If you select any one segment for editing, the change affects the entire polyline, in most cases. Figure 6-1 shows how the same sketch drawn with the Line and the PLine commands responds when you select one of the objects. A polyline is not a pickup line used by parrots in a bar.FIGURE 6-1: Results of drawing with the Line and PLine commands. Use the PLine command rather than the Line command in most cases where you need to draw a series of connected line segments. If you’re drawing a series of end-to-end segments, those segments may well be logically connected. For example, they might represent the outline of a single object or a continuous pathway. If the segments are connected logically, it makes sense to keep them connected in AutoCAD. The most obvious practical benefit of grouping segments into a polyline is that many editing operations are more efficient when you use polylines. When you select any segment in a polyline for editing, the entire polyline is selected. As covered in Chapter 19, using parametrics on line segments can often produce the same results as using the PLine command.

The PLine command can draw curved segments as well as straight ones. If you want a combination of separate linear and curved segments, you must switch between the Line and Arc commands. (I cover arcs in Chapter 7.) Using the PLine command, though, you can switch between linear or circular-curve segments in a single polyline.

A polyline can have width. Polyline segment width is visually similar to the lineweight object property in AutoCAD (which I discuss in Chapter 9) except that polyline width can vary from segment to segment, and individual segments can be tapered. Polylines are often used for the copper conductors on electronic printed circuit boards.

Polylines can be smooth curves. After drawing a polyline, you can use the PEdit command to automatically reshape the polyline into a smooth, flowing curve based on the vertex points you selected. I touch on this topic in Chapter 11.

The following sections show you how to create a line and a polyline.

Toeing the line

Unlike many AutoCAD drawing commands, Line offers limited options. It has a Close option only to create one more segment back to the first point you picked in the current run of the command, and it has an Undo option to remove the most recently drawn segment. You can repeat the Undo option back to the start of the current run of the command.

The Line command draws continuous lines. Real-world drawings include several different looks of lines, such as hidden, center, and section. Chapter 9 covers how to apply these and several other properties to lines.

Follow these steps to use the Line command:

1 Start the Line command by clicking the Line button on the Draw panel on the Ribbon, or by entering L and then pressing Enter.

2 Draw line segments by picking several random points.

3 Terminate the command by pressing Enter, Esc, or the spacebar.

4 Press Enter or the spacebar to repeat the Line command. In AutoCAD, pressing Enter or the spacebar when no command is underway always repeats the last command.

5 Draw more line segments to complete the figure.If you need to undo some line segments, enter U and press Enter.

6 Enter C and press Enter to close the figure, which draws one more segment back to the first point you picked.The Close option doesn’t appear until you've created the first two line segments. You can’t close a single line.

Pressing Enter or the spacebar whenever AutoCAD asks for a first point automatically selects the last point you picked, regardless of the previous or current command.

Connecting the lines with polyline

Drawing polylines composed of straight segments is much like drawing with the Line command, as shown in the steps in this section. The PLine command has a lot more options, however, so watch the prompts. If the Dynamic Input feature is on, press the down-arrow key to see the options listed near the cursor, or right-click to display the PLine right-click menu, or simply read the command line.

To draw a polyline composed of straight segments, follow these steps:

1 Click the Polyline button on the Draw panel of the Ribbon, or type PL at the command line and press Enter.AutoCAD starts the PLine command and prompts you to specify a start point.

2 Specify the starting point by clicking a point or typing coordinates.Now you truly do need to read the command line, because the Dynamic Input tooltip at the cursor doesn’t display any of the options. You can right-click or press the down-arrow key to see a list of the options at the cursor, as shown in Figure 6-2, but it’s usually faster to use the command line.AutoCAD displays the current polyline segment line width at the command line and prompts you to specify the other endpoint of the first polyline segment:Current line-width is 0.0000Specify next point or [Arc Halfwidth Length Undo Width]:

3 If the current line width isn’t zero, you can change it to zero by typing W to select the Width option and then entering 0 as the starting and ending widths, as shown in this command-line sequence: Specify next point or [Arc Halfwidth Length Undo Width]: WSpecify starting width <0.0000>: 0Specify ending width <0.0000>: 0Specify next point or [Arc Halfwidth Length Undo Width]: Despite what you may think, a zero-width polyline segment isn’t the AutoCAD

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