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Inside AutoCAD 14

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- 7 -

Creating Elementary Objects

by David M. Pitzer

No matter how complicated a drawing is, and no matter how many layers and linetypes it contains, almost all AutoCAD drawings are comprised of a few relatively basic shapes and forms. Circles, arcs, lines, rectangles, polygons, and ellipses are the basic elements from which both simple and complicated drawings are made. This chapter shows you the tools you will need to construct and control AutoCAD's basic drawing objects.

This chapter covers the following information:

Using the LINE Command

Perhaps the most common object in a typical AutoCAD drawing is the line. In addition to representing the shortest distance between two points, lines serve a myriad of other useful purposes; centerlines locate other geometry, border lines indicate an area's constraints, and hidden lines represent objects or boundaries that are not visible from a given point of view. All these lines are usually further identified functionally by their linetype--the period pattern of interruptions in the line's continuity. Then, of course, "normal" continuous lines are representative of things such as walls or the sides of objects. Lines are very versatile. Drawing a line is one of the most basic operations in AutoCAD.

In the following exercise, you will learn the basics of using the LINE command as you begin drawing a fixture base.

NOTE: The exercises in this chapter use the templates IAC701.dwg and IAC702.dwg files found on the accompanying CD-ROM. These drawings have most settings, linetypes, and layers already set or defined for you. In the first part of the chapter, you learn about lines, circles, arcs, and polygons. When you finish this first section, your drawing will resemble figure 7.1. Later in the chapter, you will begin a new drawing in which you will practice constructing and accurately placing ellipses.

Figure 7.1 The completed fixture base.

USING THE LINE COMMAND TO DRAW A FIXTURE BASE

1. Begin a new drawing called chap701.dwg using the IAC701.dwg as a template. Using template drawings is discussed in Chapter 3, "Setting Up the AutoCAD 14 Drawing Environment." Ensure that the current layer is Center.

2. Begin the LINE command by choosing Draw, Line. At the From point: prompt, type 38,88 and press Enter.

3. Use relative polar coordinate entry by typing @208<0 and pressing Enter at the To point: prompt. Note that the line segment is drawn with a linetype of Hidden. End the LINE command by pressing Enter.

4. Restart the LINE command by pressing the spacebar. Answer the From point: prompt by typing 112,32 and pressing Enter. Ensure that the ORTHO mode is active by double-clicking the ORTHO button on the status bar.

5. Use direct distance entry by moving the cursor above the last point and answering the To point: prompt by typing 112 and pressing Enter. End the LINE command by pressing Enter. Note that the line segment is drawn 112 units at 90 degrees to the startpoint.

6. Ensure that SNAP mode is on and restart the LINE command by typing L and pressing Enter. Respond to the From point: prompt by pressing F6 until the Coordinate display on the status bar displays absolute coordinates. Then find and pick point 156,144.

NOTE: If you miss the point in the preceding step, press Esc to cancel the LINE command. Restart the command by pressing either Enter or the spacebar.

7. At the To point: prompt, type the relative rectangular coordinate @0,-112 and press Enter. End the LINE command by pressing Enter. Your drawing should now resemble figure 7.2.

Figure 7.2 Setting up the centerlines for the fixture base.

In the preceding exercise, you used several different methods of specifying coordinate point entry while using the LINE command. You also saw how the coordinate display, which is located on the status bar at the bottom of AutoCAD's display, can be helpful in locating both absolute and relative coordinate points. Keep in mind, depending on how your snap grid is set up and the value of the actual points, the snap feature can make finding many points much easier. For points that do not lie on your current snap grid, direct coordinate entry through the keyboard is the only practical method of having line segments begin and end where you want.

TIP: In many situations, you will find yourself frequently changing the coordinate display mode as well as turning ORTHO and SNAP on and off. It is more convenient to use the function key shortcuts to control these functions. F6 controls the coordinate display, F8 toggles the ORTHO mode on and off, and F9 toggles the SNAP function.

In the following exercise, you will continue to use the LINE command as you outline the fixture base. After establishing the first corner of the base, you will use the efficient direct distance method of entering points that are orthogonal to the previous point.

USING THE LINE COMMAND TO DRAW THE FIXTURE BASE OUTLINE

1. Continue from the previous exercise. Change the current layer to OBJECT. Refer to figure 7.3 to help you identify the following points.

2. First, you will deliberately enter the wrong point to see how easy it is to recover from such a mistake. Begin the LINE command and specify the following From point: 150,48 and press Enter. Note that the point 1 falls short of the right centerline.

Figure 7.3 Completing the fixture outline.

3. To recover from your mistake, use the LINE command's Undo option by typing U and pressing Enter, and then re-enter the point at 2 by typing 156,48 and pressing Enter.

4. Now with ORTHO on and the cursor placed to the left of the previous point, use direct distance entry to specify the point at 3 by typing 108 and pressing Enter.

5. Move the cursor above the preceding point, enter 80, and press Enter to draw a line segment to 4.

6. Move the cursor to the right of 4 and enter: 108 and press Enter. The line segment from 4 to 5 is drawn.

7. Now close the outline by using the Close option of the LINE command by typing C and pressing Enter at the To Point: prompt. This completes the LINE command.

8. The line segment from 5 to 2 was drawn by mistake; it is not wanted. At the Command: prompt, issue the U command by typing U and pressing Enter. Note that all four line segments completed during the LINE command are erased. At the Command: prompt, issue the REDO command by typing REDO and pressing Enter. All four segments are redrawn.

9. To erase the last line segment, issue the ERASE command by typing E and pressing Enter at the Command: prompt. At the Select objects: prompt, type L and press Enter. Note that the last completed line segment is highlighted. Now, with the Select objects: prompt still current, press Enter. The line is erased. Your drawing should now resemble figure 7.4.

Figure 7.4 Three sides of the fixture base.

The LINE Command Options

The LINE command is straightforward and easy to use. It offers the following features:

Keep in mind that the LINE command draws line segments whose only connection is that the endpoint of one segment shares the same coordinate as the startpoint of the next segment.

TIP: If you are constructing a long series of line segments using the LINE command, break the continuity of the chain occasionally by pressing Enter three times. This has the effect of ending the series, restarting the command, and beginning a new series from the end of the last. Then if you perform a U option at a Command: prompt, it will undo only the last LINE command's series of line segments, instead of all the segments.

You can end or exit the LINE command at any time by pressing Esc or by pressing Enter at any To point: prompt.

Using the ARC Command

The ARC command is used to draw circular arcs. Its several options make constructing an arc with a variety of known parameters such as center, startpoint, chord length, radius, and so on much easier than with traditional manual drafting methods.

In the following exercise, you will draw an arc by specifying three points on its circumference. After completing the arc, you will erase it and then draw two small arcs to round the corners of the fixture base. Use the coordinate display on the status bar and the Snap feature to identify points.

USING THE ARC COMMAND TO DRAW CIRCULAR ARCS

1. Continue with the drawing from the preceding exercise. If necessary, set the SNAP mode to on by pressing the F9 key. Begin the ARC command by clicking on the ARC tool on the Draw toolbar. Respond to the arc Center/<Start point>: prompt by picking the point at 1 by typing 156,48 and pressing Enter.

2. At the prompt for the <Second point>:, pick the point at 2 by typing 196,88 and pressing Enter. Note that the arc now drags as you move the cursor.

3. At the End point: prompt, pick the point at 3 by typing 156,128 and pressing Enter. The ARC command draws the arc and terminates. Your drawing should resemble figure 7.5.

Figure 7.5 Drawing an arc using the three-point method.

4. At the Command: prompt, issue the U command by typing U and pressing Enter, and note that the arc is deleted.

5. Start the ARC command again by typing A and pressing Enter. The following prompt appears:

Center/<Start point>:

6. Respond to this prompt by typing 56,128 and pressing Enter. See 4 in figure 7.6.

Figure 7.6 Creating rounded corners with the ARC command.

7. Respond to the next prompt by typing C and pressing Enter to select the Center option. Then, at the Center: prompt, pick the point at 5 by typing 56,120 and pressing Enter.

8. Make sure that ORTHO is on (press F8 if necessary) and note that as you move the cursor the arc snaps in 90-degree increments. Move the cursor to any point near 40,120 and pick. The ARC command draws the arc; ORTHO forces it up 90 degrees.

9. Restart the ARC command by pressing Enter. At the <Start point:> prompt, type 48,56 and press Enter. The arc starts at 6.

10. At the Center/End/<Second point:> prompt, type C and press Enter to start the center option, and then enter the relative rectangular coordinate @8,0 and press Enter. This specifies the center of the arc at 7 and the Angle/Length of chord/<End point:> prompt appears.

11. Disable ORTHO mode by pressing F8 and notice that the arc drags with the cursor. Answer the current prompt by typing A and pressing Enter. Turn ORTHO back on with F8 and move the cursor anywhere above the center point. Note that the arc now snaps to 90-degree points. Pick any point directly above the center point near 8 to complete the arc and end the ARC command.

12. Save your drawing with the Quick Save option by pressing Ctrl+S.

Whenever you draw an arc, you know either its center or its startpoint and can supply the other necessary information from existing geometry in the drawing. Figure 7.7 shows the Arc cascade submenu from AutoCAD's Draw menu. This submenu conveniently lists the various choices that can be made depending on the information supplied. Starting the ARC command by using this submenu provides a shortcut through the longer prompt choices provided at the Command: prompt.

Figure 7.7 The Arc submenu offers 10 choices.

The ARC Command Options

The ARC command requires three pieces of information to complete an arc, one of which must be either the center or startpoint. The other required parameters can be supplied in various combinations. The following list explains these combinations:

TIP: There probably is no other AutoCAD command that seems at times to be as "uncontrollable" as the ARC command. The trick in drawing arcs with other than the basic and simple 3-point or start-center-end options is knowing how to force the arc in the direction you desire. Understanding that AutoCAD, by default, thinks of arcs as developing counterclockwise from the startpoint is the key. To force an arc to proceed clockwise requires you to input a negative angle, for example, or to supply a negative distance for a length of chord parameter. The same type of entries control whether an arc is drawn as a minor or major arc. Armed with this knowledge and a little practice, your arcs can come out correctly on the first try.

The ARC command's Continue option is often convenient when arcs are associated with line segments. The following exercise demonstrates this feature of the ARC command.

PUTTING LINES AND ARCS TOGETHER

1. Continue from the drawing in the preceding exercise. Make sure ORTHO mode is active. Refer to figure 7.8 for this exercise.

Figure 7.8 Use Continue options to draw slots.

2. Start the LINE by typing L and pressing Enter, or clicking on the Line tool on the Draw toolbar. At the From point: prompt, pick at point 1 by typing 64,56. Then at the To point: prompt, type the relative coordinate @12,0 and press Enter. See 2 for reference.

3. Click on the Arc tool to cancel the LINE command and start the ARC command. Press Enter at the following prompt:

_Center/<Start point:>

4. This activates the Continue option of the ARC command and starts an arc tangent to the line. Now pick the point at 3 by typing 76,76.

5. Now restart the LINE command by clicking the Line tool again. Press Enter at the From point: prompt. This activates the Continue option and starts the line tangent to the arc. A new prompt appears. Respond as follows:

Length of line: 12 ¯

6. Draw a line to 4. Now again choose the ARC command. Note that the LINE command is canceled. At the Center/<Start point:>, press Enter. The new arc starts tangent to the line. Pick the endpoint of the lower slot line at 1.

7. Your drawing should now resemble figure 7.8. Press Ctrl+S to save this drawing in its present form.

The drawing shows the fixture base with rounded corners on the left side. After the preceding exercise, you now have the tools to create such corners with the Continue options of the ARC and LINE commands.

NOTE: Chapter 11, "Advanced Geometry Editing," explains the use of the FILLET command, which provides an easy alternative way to create arcs tangent to lines.

Using the CIRCLE Command

Another basic AutoCAD shape is the circle. Circles are used to represent holes, wheels, shafts, columns, trees, and so on. Several methods of drawing circles exist and, unlike manual drafting, constructing circles in AutoCAD is quick and accurate. Circles have centers, diameters, radii, and tangent points. Providing a combination of these parameters will enable you to draw any circle anywhere you want.

In the following exercise, you construct a few basic circles as you add holes and sleeves to the fixture base.

ADDING HOLES AND SLEEVES BY DRAWING CIRCLES

1. Continue in the drawing from the previous exercise. Refer to figure 7.9 during this exercise.

Figure 7.9 Drawing and placing circles.

2. Start the CIRCLE command by typing C and pressing Enter, or picking the Circle tool from the Draw toolbar. The following prompt appears:

CIRCLE 3P/2P/TTR/<Center point>:

3. Respond to this prompt by picking a point at 1 by typing 156,88. Move the cursor and watch the radius and circle drag. The coordinate display should show changing X,Y coordinates. If it doesn't, click on the display until it does. Now click twice in the coordinate display to change to a polar coordinate display. Slowly move the cursor and pick the point 4.00@<0.00 at 2. AutoCAD draws the circle.

4. Press Enter or the spacebar to restart the CIRCLE command. At the circle prompt, type @ and press Enter. Note that key combination re-enters the last point and establishes the center of a new circle. Respond to the next prompt as follows:

Diameter/<Radius> <4.00>: D ¯

5. This causes the command to prompt for a diameter. Type 20 and press Enter. This specifies the diameter and draws the circle.

6. Now choose Draw, Circle, 3 Points. The following prompt appears:

_circle 3P/2P/TTR/<Center point>: _3p First point:

7. Respond to this prompt by picking the point 104,88 at 3. This sets the first of the three points at 8 units to the left of the centerlines. Respond to the prompts for the other two points as follows:

Second point: pick the point 112,96 at 4

Third point: pick the point 120,88 at 5

8. AutoCAD draws the circle with the three points you picked on the circumference. Now press Enter to restart the CIRCLE command with the default center-radius mode:

CIRCLE 3P/2P/TTR/<Center point>:

9. At the preceding prompt, pick point 112,88 at 6. This sets the center point. Now experiment with the effects of ORTHO mode. Turn ORTHO mode off by pressing F8. Move the cursor around while watching the polar coordinate display. Pick when a radius of 20 displays. AutoCAD draws the circle with a radius of 20 units.

CIRCLE Command Options

The CIRCLE command provides you with several options to control the sequence in which you create circles. In addition to the default center-point, radius mode, you can create a circle by specifying three points on the circumference or by selecting two objects (lines, circles, or arcs) to which the circle is to be tangent and then specifying a radius. The CIRCLE command offers the following options:

NOTE: Note the difference between Center point/Diameter and the 2P option. Both options enable you to specify a diameter, but if you pick the second point with Center point/Diameter, it merely indicates the diameter's distance and the circle does not draw through the point. If you pick two points with 2P, a circle appears between those two points and the distance is the diameter. The 2P option enables you to draw a diameter circle the way most of us intuitively think about the term diameter.

In the following exercise, you practice using the TTR option of the CIRCLE command.

PRACTICING CIRCLES WITH THE TTR OPTION

1. Continue in the drawing from the preceding exercise. Refer to figures 7.10 and 7.11 during this exercise.

Figure 7.10 Placing circles using the Tangent-Tangent-Radius method.

2. Start the CIRCLE command by clicking the Circle tool from the Draw toolbar. Respond to the prompt as follows:

_circle 3P/2P/TTR/<Center point>: T ¯

3. This specifies the TTR option. The Enter Tangent spec: prompt appears.

4. Respond to this prompt by picking anywhere on the line 1. The Enter second Tangent spec: prompt appears.

5. Respond to this prompt by picking anywhere on the circumference of the circle at 2. Respond to the following prompt as shown:

Radius: 20 ¯

6. AutoCAD draws the only circle 5 that is tangent to both the circle at 2 and the line at 1 having a radius of 20 units (see fig. 7.11). Issue the Undo command to delete the last circle. Note that the circle is deleted.

7. Now repeat steps 2 through 5, but at step 5 type 50 and press Enter. Once again, AutoCAD draws the only possible circle 6 tangent to both the circle at 3 and the line at 4 having a radius of 50 units (see fig. 7.11).

Figure 7.11 Drawing circles with the TTR option.

8. Issue the Undo command again to delete the last circle drawn.

9. Save your drawing by pressing Ctrl+S.

NOTE: When specifying the TTR option, you may encounter the message Circle does not exist. This indicates that no possible circle of the radius you specified or tangent to the two points you chose, or both, exists. Most often, the radius specified is too small.

Using the POLYGON Command

In AutoCAD, the POLYGON command is used to create regular polygons with sides of equal length. You can draw a polygon composed of from 3 to 1,024 sides. After you specify the number of sides, several options are available to complete the polygon.

In the following exercise, you practice drawing a polygon representing a mounting hole on the fixture base.

ADDING A MOUNTING HOLE WITH THE POLYGON COMMAND

1. Continue in the drawing from the preceding exercise. Refer to figure 7.12 during this exercise.

Figure 7.12 Adding mounting holes with the POLYGON command.

2. Start the POLYGON command. Choose Draw, Polygon. Answer the prompts as follows:

Polygon Number of sides <4>: 6 ¯ Edge/<Center of polygon>: 62,112 ¯ 1 Inscribed in circle/Circumscribed about circle (I/C) <I>: C ¯ Radius of circle: 6 ¯

3. AutoCAD draws the hexagon. Note that the bottom edge of the hexagon 2 is drawn at 0 degrees.

4. Press the spacebar to restart the POLYGON command. Answer the prompts as follows:

Polygon Number of sides <6>: ¯ Edge/<Center of polygon>: 80,112 ¯ 3 Inscribed in circle/Circumscribed about circle (I/C) <I>: I ¯ Radius of circle: 6 ¯

5. AutoCAD draws the hexagon 4. Note that the default number of sides changed from 4 to 6 for the repeated command. Also note the difference in size between the inscribed and circumscribed figures (refer to fig. 7.12).

TIP: AutoCAD's POLYGON command produces polygons that are composed of Light Weight Polylines. Light Weight Polylines are beneficial because they can be exploded into individual line segments for editing. Their width can be changed by using the PEDIT command. You'll learn about both of these techniques later in this book.

AutoCAD's POLYGON command provides a convenient way to draw regular (equilateral) multi-sided polygons, including triangles. Several options make sizing and placing of the final polygon relatively easy.

The fixture base drawing that has gradually grown during this chapter is almost complete. In the following exercise, you will use the line/arc continue method of "rounding corners" that you learned earlier in this chapter to complete the drawing.

COMPLETING THE FIXTURE BASE WITH A ROUNDED CORNER

1. Continue with the drawing from the preceding exercise. Refer to figure 7.13 during this exercise. Make sure that coordinate readout is active. If necessary, press F6 to make it active.

2. Start the LINE command by typing L and pressing Enter. At the From point: prompt, find and pick the point 156,128 1.

3. At the To point prompt:, type the relative coordinate: @48,-24 and press Enter. A line is drawn to 2.

Figure 7.13 Finishing the fixture base with a rounded end.

4. End the LINE command by pressing Enter. Start the ARC command by typing A and pressing Enter. Press Enter again to use the Continue option. At the End point: prompt, type the relative polar coordinate: @32<270. AutoCAD draws the arc 3.

5. Now start the LINE command again and press Enter to activate the Continue option. At the Length of line: prompt, find and pick point 156,48 4. (If necessary, press F6 until the coordinate display shows absolute coordinates.) Press Enter to end the LINE command.

6. This completes the fixture base and your drawing should look like figure 7.1 at the beginning of this chapter. You are now finished with this drawing.

So far in this chapter you have learned about the basic AutoCAD drawing elements of lines, circles, arcs, and polygons. You will use these elements over and over again in most of your drawings. You have also learned how AutoCAD gives you a large amount of flexibility in constructing and placing these basic elements. Next you will learn how to draw ellipses.

Drawing Ellipses

Until AutoCAD Release 13, AutoCAD constructed ellipses using a special line object called a polyline. Polylines are very versatile drawing elements, and you will learn about them in Chapter 8, "Creating Polylines and Splines," but they do not make true ellipses. In Release 14, AutoCAD can draw mathematically true ellipses with geometric centers and accurate quadrant points.

AutoCAD is still capable of constructing elliptical representations of ellipses using polylines; however, now the system variable PELLIPSE determines the type of ellipse drawn. A value of 1 creates a polyline representation; a value of 0 creates a true ellipse.

TIP: In Release 14, the default method of drawing ellipses is to draw true ellipses. Unless you have a specific reason to use the less-accurate polygon approximation, leave the system variable PELLIPSE set to 0 and draw true ellipses. Polygon ellipses offer little, if any, advantage.

Ellipses are somewhat complicated geometric figures, but if you have a basic understanding of the geometry of an ellipse, AutoCAD enables you to draw them easily. Ellipses have both a major axis and a minor axis, as shown in figure 7.14. Although from a mathematical point of view an ellipse has two "centers" or foci, AutoCAD considers the geometric center to be the intersection of the two axes. The quadrants of an ellipse are the points of intersection between the axes and the ellipse. In AutoCAD, you can use both the quadrants and center of an ellipse as object snap points.

Figure 7.14 The geometry of an ellipse.

AutoCAD offers you several ways to specify the various parameters of an ellipse.

ELLIPSE Command Options

When you issue the ELLIPSE command, the following prompt appears:

Arc/Center/<Axis endpoint 1>:

NOTE: In reckoning angles for elliptical arcs, the direction of the first point of the major axis is considered 0 degrees. If the system variable ANGDIR is set to 0 (the default), angles for the elliptical arc are measured counterclockwise; if set to 1, they are measured clockwise. If the minor axis is defined first, the major axis zero point is 90 degrees in a counterclockwise direction. If you choose the Included angle option, the angle is measured from the startpoint, not the 0 degree point.

TIP: When specifying elliptical arc angles, it is helpful to set the coordinate display on the status bar to indicate polar coordinates. Cycling through the coordinate display modes by pressing the F6 key enables you to do this.

In the following exercises, you practice drawing ellipses in a typical 3-view mechanical drawing. During the exercises, you will utilize the object snap techniques learned in Chapter 6, "Creating Drawings with R14." In this exercise, you first use a full set of construction lines to draw an ellipse in one view, then a reduced set of construction lines provides the information you need to draw an ellipse in another view.

DRAWING ELLIPSES IN A 3-VIEW DRAWING

1. Begin a new drawing called CHAP7-2.dwg. Use the IAC702.dwg template found on the accompanying CD-ROM. Your drawing will initially resemble figure 7.15. Your first step will be to add an ellipse to the top view.

Figure 7.15 You will add ellipses to this 3-view drawing.

2. Start the ELLIPSE command by clicking on the Ellipse tool on the Draw toolbar. The following prompt appears:

Arc/Center/<Axis endpoint 1>:

3. Choose the default endpoint option by typing int and pressing Enter to activate the Intersection osnap mode. Move the osnap box over the intersection at 1 of figure 7.15 and pick. When the following prompt appears, type the following:

Axis endpoint 2: int ¯

4. Move the osnap box over the intersection at 2 and pick. These two picks establish one axis of the ellipse. The following prompt appears:

<Other axis distance>/Rotation:

5. Note that the hole you are representing is 1 unit in diameter and that the "other" axis distance is half that distance from the center of the ellipse. Therefore, respond to the above prompt by entering: .5 and pressing Enter. AutoCAD draws the ellipse.

Ensure that the ORTHO mode is active before beginning the next step.

6. Restart the ELLIPSE command by pressing Enter. This time, choose the Center option by answering the initial prompt as follows:

Arc/Center/<Axis endpoint 1>: C ¯

7. Respond to the Center of ellipse: prompt by invoking the Intersection osnap again (int and press Enter) and picking the intersection at 3.

8. Respond to the Axis endpoint: prompt using direct distance entry. Drag the cursor to the left or right of the center point established in step 7 and enter .5 and press Enter. The ellipse is started and the following prompt appears:

<Other axis distance>/Rotation:

9. Note that you do not have the information immediately available to establish the other axis distance in this view. Therefore, select the Rotation option by entering r and pressing Enter at the current prompt. The following prompt appears:

Rotation around major axis:

10. Notice that the hole you are representing is at an angle of 45 degrees to this view. Therefore, respond to the current prompt by entering: 45 and pressing Enter. AutoCAD draws the ellipse. You are finished with this drawing.

In the preceding exercise, you constructed an ellipse by specifying the axes and then by specifying the center and a rotation about the major axis.

NOTE: Although construction lines were used in the preceding exercise to assist in visualizing the geometry of the ellipses, both of the ellipses could have been constructed utilizing only point filters and object snaps methods.

Summary

In this chapter, you have learned to use the commands AutoCAD provides for drawing basic objects, from simple lines to complicated arc segments. Mastering their use forms the basis of the range of skills required to use AutoCAD effectively.

Although the LINE command involves few options, used in combination with the other basic objects and drawing aids, such as ORTHO and object snaps, it is a fundamental component of most AutoCAD drawings.

When drawing circles and arcs, several methods are available. The method you select depends on the information that you have available. You can often use more than one of the methods to accomplish the task. Understanding how and when to use each method enables you to quickly construct complex designs.

Polygon objects are common figures found in many AutoCAD drawings. Knowing how to construct them quickly and accurately increases your efficiency.

True mathematical ellipses and elliptical arcs are possible in AutoCAD. Ellipses have true center and quadrant points to which you can snap. These objects are also frequently used to represent circular objects viewed in axonometric views.

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