174 Part II: Let There Be Lines
Figure 8-5: A plethora of polylines.
The LINE and PLINE commands work well for drawing a series of end-to-end single lines, but what if you want to draw a series of double lines to represent, for example, the edges of a wall or roadway? Here are some options:
Use the AutoCAD MLINE command to draw multilines — series of two or more parallel straight lines. The AutoCAD multiline feature was full of limitations when it debuted way back in 1994 (in the notorious
Release 13), and despite some minor tweaks in AutoCAD 2006, it hasn’t improved significantly since then. It exists mostly for compatibility with MicroStation files. Look up the MLINE and MLSTYLE commands in AutoCAD’s online help system if you’d like to tangle with this feature, but be prepared to spend time experimenting and struggling.
Use the PLINE command to draw a single set of connected line and/or arc segments, and then use the OFFSET command to create one or more sets of parallel segments. Chapter 11 covers the OFFSET command.
In AutoCAD LT only, use the DLINE (DL), or Double Line, command to draw pairs of parallel line and/or arc segments. AutoCAD LT doesn’t include the MLINE command, which, given MLINE’s problems, is more of a blessing than a limitation. AutoCAD, on the other hand, doesn’t include the DLINE command. (Score one for the little brother!)
Squaring off with rectangles
You can use the PLINE or LINE command to draw a rectangle, segment by segment. In most cases, though, you’ll find it easier to use the specialpurpose RECTANG command. The following procedure demonstrates how:
1.Set an appropriate layer to be current.
2.Click the Rectangle button on the Home tab’s Draw panel, or type REC and press Enter.
www.it-ebooks.info
Chapter 8: Along the Straight and Narrow 175
AutoCAD starts the RECTANG command and prompts you to specify a point for one corner of the rectangle. The command line shows
Specify first corner point or [Chamfer/Elevation/ Fillet/Thickness/Width]:
You can add fancy effects with the additional command options. The default options work best for most purposes. Look up RECTANG in the AutoCAD help system if you want to know more about the options.
3. Specify the first corner by clicking a point or typing coordinates.
AutoCAD prompts you to specify the other corner of the rectangle — the one that’s diagonally opposite from the first corner.
Specify other corner point or [Area/Dimensions/
Rotation]:
4. Specify the other corner by clicking a point or typing coordinates.
If you know the size of the rectangle that you want to draw (for example, 100 units long by 75 units high), type relative coordinates to specify the dimensions — for example, @100,75, or just 100,75 if Dynamic Input is enabled. (Chapter 7 describes how to type coordinates.)
AutoCAD draws the rectangle.
Unlike the neglected MLINE command, the RECTANG command has improved considerably since its debut. You can specify a rotation angle and — very handy for space planners — you can provide one dimension and an area. RECTANG will calculate the length of the other side and draw the rectangle.
Choosing your sides with polygon
Rectangles and other closed polylines are types of polygons, or closed figures with three or more sides. The AutoCAD POLYGON command provides a quick way of drawing regular polygons — polygons in which all sides and angles are equal. This is different from an escaped parrot.
The following procedure demonstrates the POLYGON command:
1.Set an appropriate layer to be current.
2.Click Polygon on the Home tab’s Draw panel’s Rectangle drop-down button, or type POL and press Enter.
AutoCAD starts the POLYGON command and prompts you to enter the number of sides for the polygon.
Enter number of sides <4>:
3.Type the number of sides for the polygon that you want to draw and press Enter.
Your polygon can have between 3 and 1,024 sides.
www.it-ebooks.info
176 Part II: Let There Be Lines
AutoCAD prompts you to specify the center point of the polygon.
Specify center of polygon or [Edge]:
You can use the Edge option to draw a polygon by specifying the length of one side instead of the center and then the radius of an imaginary inscribed or circumscribed circle. The imaginary circle method is much more common.
4. Specify the center point by clicking a point or typing coordinates.
AutoCAD prompts you to specify whether the polygon will be inscribed in (that is, the corners touch the circumference of the circle) or circumscribed about (that is, the sides are tangent to the circle) an imaginary circle whose radius you will specify in Step 6. Note that circumscribed has nothing to do with being Jewish.
Enter an option [Inscribed in circle/Circumscribed about circle] <I>:
5. Type I (for inscribed) or C (for circumscribed), and press Enter.
The command line prompts you to specify the radius of an imaginary circle.
Specify radius of circle:
6.Specify the radius by typing a distance or clicking a point.
AutoCAD draws the polygon.
If you type a distance or you click a point with ortho turned on, the polygon will be aligned orthogonally, as shown in Figure 8-6.
Rectangles and polygons aren’t special object types. They are simply regular polylines that have been constructed by special command macros.
Figure 8-6 shows the results of drawing plenty of polygons — a practice known as polygony, which, as far as we know, is legal nearly everywhere.
Figure 8-6: A polygonal part.
www.it-ebooks.info
9
Dangerous Curves Ahead
In This Chapter
Rounding the curves with circles, arcs, splines, and clouds
Eccentric ellipses
Dunking for donuts
Making your points
Although straight-line segments predominate in many CAD drawings, even the most humdrum, rectilinear design is likely to have a few
curves. And if you’re drawing Audi car bodies or Gaudí buildings, your drawings are going to contain a lot of curves! Your drawings should also have a point; in fact, they may have several points, so at the end of this chapter, we fill you in on creating point objects in AutoCAD. But to begin, we show
you how to use the following AutoCAD curve-drawing commands:
CIRCLE: Draws circles. (You were expecting hyperbolic paraboloids, maybe?)
ARC: Draws circular arcs — arcs with center points and fixed radii, not arcs cut from ellipses, parabolas, or some other complex curve.
ELLIPSE: Draws ellipses and elliptical arcs.
SPLINE: Draws smoothly flowing curves of a variety of shapes.
DONUT: Draws filled-in rings and circles. Unfortunately, the filling isn’t jelly.
REVCLOUD: Draws freeform “clouds,” the most common application of which is to indicate revised areas in the drawing.
www.it-ebooks.info