Other Dimensions

Several other dimensioning types are worth mentioning. These dimension types are not linear and serve specific purposes. Depending on your discipline, you may have a use for some of these types. For example, a mechanical part designer will make heavy use of radius and diameter dimension types, whereas a civil engineer will make use of datum dimension types.

Radius and Diameter Dimensions

Radius and diameter dimensions are used to dimension the size of an arc or circle, regardless of the type of object. If you create a polyline with an arc in it, for example, you can use either dimension type to dimension the arc. If you select the Center Mark check box in the Dimension Styles dialog box, the center mark will automatically be used with radius and diameter dimensions when the dimension text is placed outside the circle or arc. Other than that, the placement of radius and diameter dimensions is relatively straightforward. With these dimension types, you simply pick the arc or circle to dimension, then the dimension line location. Features of the Dimension Style dialog box will be presented in Chapter 18.

Angular Dimensions

Angular dimensions are used to dimension the angle between two non-parallel lines. Of course, when you dimension angles between two lines, four angles are possible: one on each side of the intersection point of the two lines. Where you place the dimension line determines which angle is measured. Like radius and diameter dimensions, angular dimensions are straightforward.

The following exercise demonstrates how to make use of the DIMANGULAR and DIMRADIUS commands.

Exercise 17.5 Dimensioning Angles and Radii

1.	Load the file 17TUT06.DWG from the accompanying CD. This file contains a simple filleted triangular object that you will dimension.
2.	To start, choose Dimension, Radius to activate the DIMRADIUS command.
3.	You will be prompted to select a circle or an arc. Select one of the filleted corners of the object.
4.	You will immediately see the dimension appear. By moving the mouse around, you can see different looks for the dimension. Place the dimension outside the triangular area.
5.	Now, select Dimension, Angular to invoke the DIMANGULAR command.
6.	You will be prompted to select a line, arc, or circle or a first vertex. Click on the left vertical line of the shape.
7.	You will then be prompted to select a second line. Click on the angled line on the top of the shape.
8.	Now, move the mouse around in a circle around the upper-left corner of the shape. You will see that you have four possible dimensions. Place the dimension inside the shape so it measures the angle as 57 degrees.
9.	Close this drawing without saving.

Ordinate Dimensions

Ordinate dimensions are used to dimension a specific coordinate, such as a point from a civil survey. For example, a civil survey relies upon a set of three-dimensional data points on which to base a topography. These coordinates are labeled using an ordinate dimension type, which labels the point’s exact X and Y coordinates.

When using ordinate dimensions, you may dimension the X- or Y- axis points, called datums. You also have the option to create a leader-like ordinate dimension that has text before or after the coordinate. Figure 17.11 shows you an ordinate dimension.

The ordinate dimension command can be accessed on the pull-down menu, on the toolbar, or by typing DIMORD at the Command: prompt. When you select this command, you are prompted to select the feature, or the coordinate, to dimension. After you select the coordinate, you can select the type of ordinate dimension you want to use.

The four types of ordinate dimensions are X datum, Y datum, Mtext, and Text. The X and Y datum points produce the corresponding coordinate. Mtext pops up the Multiline Text Editor dialog box so you can add text before and after the Datum dimension. The datum dimension appears as <> in the Multiline Text Editor dialog box. In fact, the first set of <> are used by all dimensions to produce the default dimension value. Figure 17.12 shows you the Multiline Text Editor dialog box when used with the ordinate Mtext option. The Text option enables you to modify the text of the Datum dimension, without having to use the Multiline Text Editor.

The following exercise shows you how to use ordinate dimensions to dimension several survey points. In this exercise, the PDMODE system variable has been set so that points appear as crosses.

Exercise 17.6 Using Ordinate Dimensions

1.	Load the file 17TUT03.DWG from the accompanying CD.
2.	Choose Ordinate from the Dimension pull-down menu or toolbar if it is open.
3.	Using a node object snap mode, click on one of the crosses and place the dimension to the right of the point. Be sure you use the Polar Snap feature to place the dimension along the X-axis.
4.	Repeat steps 3 and 4, but place the dimension above the cross this time.
5.	Repeat steps 3 through 5 for several other crosses so you get a little practice. Figure 17.13 shows you this file with a few ordinate dimensions added. Figure 17.13. The points dimensioned with ordinate dimensions.
6.	Close the drawing without saving it.

Tolerance Dimensions

Another dimension type is the tolerance dimension. Tolerances are used to provide constraints within which you can construct the drawn object. For example, you might construct a mechanical part and specify that its length may be 2.0 cm + or – 0.001 cm.

AutoCAD provides you with methods of creating tolerance dimensions. One method is to specify the tolerances in the Dimension Styles dialog box. The tolerances are then automatically added to the dimension text as you place dimensions. The second method is to use the tolerance command and place tolerance symbols on the drawing. The second method is the method discussed in the following section. Figure 17.14 shows a standard tolerance symbol inside of AutoCAD.

Placing Tolerance Symbols in a Drawing

Under the Dimension menu and toolbars, you find a Tolerance option. Choosing this option displays the Geometric Tolerance dialog box, shown in Figure 17.15. The Geometric Tolerance dialog box is used to select the appropriate type of tolerance you want to use, through the use of industry standard tolerance symbols.

In the Geometric Tolerance dialog box, you can specify values for tolerances 1 and 2, as well as round symbols. You can also specify up to three datums, such as a material condition and a value for that condition. You can also specify height, projected tolerance zones, and datum identifiers.

At the far left of the Geometric Tolerances dialog box, you will find two black boxes for symbols. If you click on one, you will see the Symbols dialog box (see Figure 17.16). In this dialog box, notice the several different symbols, each representing a different geometric characteristic. When you choose one of the symbols, the selected tolerance method is then placed in the tolerance dimension itself. After you click on a geometric tolerance type, you are transferred back to the Geometric Tolerance dialog box where you may then enter the values for the tolerances.

Creating Annotation with a Leader

Leaders are the most popular method of adding notes and pointing out specific aspects of a drawing. A leader is a line with an arrowhead pointing to a specific feature with some sort of text or graphics at the end of the line. For example, you might create a wall section of a house and use leaders to point out specific materials in the section.

A leader is easily created by selecting the LEADER command from the Dimension pull-down menu. When prompted for the first point, select the point where you want the arrowhead of the leader to appear. Then, you simply draw as many straight leader segments as you like. When you are done, press Enter, enter your text, and press Enter twice more to exit the command. This chapter will focus on several more advanced features of leaders, such as using the Multiline Text Editor dialog box to enter multiline text and using splines instead of straight line segments in your leaders.

Leader Options

When you select the LEADER command, you are prompted for a point. This point is, of course, the location of the arrowhead. After you select the start point and then the second point, you are presented with the options for the LEADER command. Usually, you type in a single line of text to complete the LEADER command. Occasionally, however, you may want to select one of the three options available to you. These options are as follows:

• Format. This option enables you to specify a variety of formats for the leader, such as using splines instead of straight-line segments, or whether you need to have an arrowhead.

• Splines. A spline is a smooth curved line, instead of straight-line segments. When you select this option, your leader line is drawn using the AutoCAD Spline command. Note that this is not a smooth polyline, but a true spline.

• Straight. The Straight option creates a series of straight-line segments. You may select either straight or spline, but you cannot have both. AutoCAD does not enable you to draw a leader line with both straight and curved segments. Figure 17.17 shows you one leader with splines and another leader with straight lines.

  Figure 17.17. A leader with splines versus one without splines.

  

• Arrow. The Arrow option defines whether an arrowhead is drawn. If you want to change the arrowhead to something other than a standard arrow, you must do so in the Dimension Styles dialog box, discussed in Chapter 18.

• None. This option removes all formatting, including arrowheads, and draws straight-line segments.

  Tip

  Each of the format options must be set each time you use the LEADER command.

  
  

• Annotation. This option, which is the default, enables you to control how you place your text in the LEADER command.

• Undo. This option removes the last line segment you drew in the LEADER command.

Annotation Options

The annotation options provide you with some control over what is placed at the end of the leader line. When you select the Annotation option, you are presented with five options at the command line: Tolerance, Copy, Block, None, and Mtext, which is the default. All text in leaders is now placed using Mtext. If you select this option, you are presented with the Multiline Text Editor dialog box, where all the options of formatting Mtext are available to you. See Chapter 15, “Text Annotation,” for more information about the Mtext command.

Three of the four other annotation options enable you to place a variety of objects rather than text at the end of the leader. You can place a tolerance dimension, copy an object from somewhere else in the drawing, or insert a block. Selecting one of these options launches the respective command. The last option is None, which removes all formatting.

The following exercise shows you how to create leaders on a simple architectural wall section.

Exercise 17.7 Creating Leaders in AutoCAD 2002

1.	Load the file 17TUT04.DWG from the accompanying CD. Figure 17.18 shows you how the drawing should appear at the end of this exercise. Use it as a reference for completing this exercise. Figure 17.18. The wall section as it will appear at the end of the exercise.
2.	On the left side of the wall, create straight leaders by choosing the LEADER command from the Dimension pull-down menu or toolbar.
3.	When asked for the first point, select a point close to the arrowhead location of the 2 × 4 Wood Stud leader.
4.	Select the second point of the leader, as shown in Figure 17.18.
5.	At this point, you are presented with the leader options at the Command: prompt. Press Enter to accept the default Annotation Option, which enables you to add text to your leader.
6.	Type 2 × 4 Wood Stud and press Enter to complete the leader.
7.	Repeat steps 3 through 5 for the rest of the straight leaders shown in Figure 17.18.
8.	For the spline leaders shown in Figure 17.18, again enter the Leader command.
9.	Select your start point and a second point so you are presented with the options for the command.
10.	Type F for the format options.
11.	Type S for spline. Now the line is a spline. Draw the rest of the line and enter the appropriate text.
12.	The detail is now complete. Close the drawing without saving it.