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Measurement Commands

The DIVIDE command divides an object into equally spaced sections. The MEASURE command divides an object into sections of a specified length. These commands are useful in many fields — you might need to space bolt holes evenly around the edge of a bushing, or place fence studs along the edge of a plot every 5 feet.

	Dividing objects
	The DIVIDE command divides an object into equal sections. DIVIDE does not break the
	object — it simply places point objects along the selected object. You can then use the Node
	object snap if you want to draw from those points.
	To divide an object, choose Draw Point Divide. Select the object you want to divide. The
	command responds with the Enter the number of segments or [Block]: prompt. Type
	in the number of segments that you want to create. AutoCAD places the point objects and
	ends the command.
Tip	Remember that you can set the point display by choosing Format Point Style. An easy-to-
	see point style is especially useful for the DIVIDE command. Specify the point style before
	using the command.
	To create eight segments, for example, you need to place seven point objects. If you have in
	your mind the number of point objects you want, add one when specifying the number of
	segments.
	You can use the Block option to place a block of your choice along the object instead of a
	point object. The block must exist in your drawing. (Chapter 18 covers blocks.) If you choose
	the Block option (right-click and choose Block), the option responds with the Enter name
	of block to insert: prompt. Type the name of the block. The prompt asks, Align block
	with object? [Yes/No] <Y>. Answer Y or N depending on whether you want to align the
	block with the object.
Note	Aligning a block is appropriate for curved objects and blocks that are not completely
	symmetrical.
	The prompt asks for the number of segments you want, and you type that number, as
	described earlier. Figure 12-11 shows an electrical schematic. Here you want to divide a line
	so that you can evenly space wires entering the ignition module. Four wires need to come in
	so that the line was divided into five segments, using an easy-to-see point object.

Measuring objects

The MEASURE command is similar to the DIVIDE command except that you specify the distance between point objects instead of the total number of segments. The command starts measuring from the endpoint closest to where you pick the object. MEASURE does not break the object — it simply places point objects along the object. You can then use the Node object snap if you want to draw from those points.

You can practice using the DIVIDE command after the next section.

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Point objects Divided line

Figure 12-11: Dividing a line into five segments by using point objects.

Thanks to Robert Mack of the Dexter Company, Fairfield, Iowa, for this drawing.

To measure an object, choose Draw Point Measure. Select the object you want to measure. The command responds with the Specify length of segment or [Block]: prompt. Type the segment length where you want to place the point objects and end the command.

Remember that you can set the point display by choosing Format Point Style. An easy-to- see point style is especially useful for the MEASURE command. Specify the point style before using the command.

As with the DIVIDE command, you can place a block along the object using the Block option, as long as the block exists in your drawing. The option prompts you for the name of the block and lets you choose if you want to align the block with the object. The prompt asks for the segment length, and you type in the lengths between the points, as described earlier. Figure 12-12 shows a plat drawing with one side of a lot measured into 20-foot segments.

Figure 12-12: Measuring a line into 20-foot segments by using point objects.

Thanks to Bill Maidment of Caltech, Inc. Fairfield, Iowa, for this drawing.

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On the	The drawing used in the following Step-by-Step exercise on using the DIVIDE and MEASURE
CD-ROM	commands, ab12-a.dwg, is in the Drawings folder on the CD-ROM.

STEP-BY-STEP: Using the DIVIDE and MEASURE Commands

1.Open ab12-a.dwg from the CD-ROM if it isn’t already open from the previous exercise.

2.If you didn’t do the previous exercise, use ZOOM Window to zoom in to the parcels labeled D and E, as shown in Figure 12-13.

3.Choose Format Point Style and choose the fourth style in the first row. Choose Set Size Relative to Screen and set the size to 5%. Click OK.

4. Choose Draw Point Divide. At the Select object to divide: prompt, choose 1 in Figure 12-13. At the Enter the number of segments or [Block]: prompt, type

3 . The command places two points along the line, dividing it into three segments. (If you want, draw lines from the points perpendicular to the opposite side of the parcel to divide it into three parcels.)

5.Choose Draw Point Measure. At the Select object to measure: prompt, choose

2 in Figure 12-13. At the Specify length of segment or [Block]: prompt, type

120 (10 feet). The command places two points along the line.

6.Do not save your drawing. Keep it open if you’re continuing to the next exercise.

2

1

Figure 12-13: The site plan zoomed in to parcels D and E.

AutoCAD’s Calculator

AutoCAD’s calculator is a geometric calculator that not only can calculate numbers like an ordinary calculator but also can calculate points and vectors. The calculator supports object snaps (except apparent intersection, extension, and parallel) and has its own functions so that it’s actually a simple programming language. In fact, you can even use AutoLISP variables in your expressions. Here I show you the basics of the calculator.

288 Part II Drawing in Two Dimensions

To start the calculator, type cal on the command line. If you’re in the middle of a command, type 'cal .

Calculating numbers

Calculating numbers is straightforward and uses standard rules of precedence. The following illustrates this point:

Command: cal

.>> Expression: 3*(2+3)/5-1 2.0

Because the 2+3 sum is in parentheses, it is calculated first so that the expression multiplies 3 by 5 (which is 15), divides it by 5 (which is 3), and subtracts 1 (which is 2).

Using CAL in this way is just like having a handheld calculator by your computer.

When you use CAL transparently, AutoCAD assumes you want the result to be a response to a prompt. Let’s say you want to draw a horizontal line. You know it has to be the total of two other lines whose length you know. Follow the prompts:

Turn on ORTHO.

Start the LINE command.

Specify first point: Pick the start point for the line. Move the cursor to the right to draw at a zero-degree angle and so you can use Direct Distance Entry.

Specify next point or [Undo]: ‘cal >> Expression: 3.953+6.8725 10.8255

End the LINE command. AutoCAD draws a line whose length is the sum of the two numbers.

You can add feet and inches as well. Use the format 6'5" or 6'-5". Don’t put any spaces between the feet and inches. With the calculator, all inches must be marked with a double prime ("), unlike regular AutoCAD command-line usage. (See the sidebar “The ins and outs of fractional inches in CAL.”)

Using coordinates

You can use coordinates in CAL expressions. Coordinates are enclosed in square brackets. Let’s say you want to draw a line that is equal to the length of two other objects in your drawing that you happen to know are 3.953 and 6.8725 units long. You want the line to be at a 20degree angle. At the Specify next point or [Undo]: prompt, start CAL transparently:

>> Expression: [@(3.953+6.8725)<20]

This creates a relative polar coordinate whose length is the sum of two numbers.

Using object snaps

You can use the object snaps as part of CAL expressions. When you press Enter after completing the expression, AutoCAD prompts you for the objects for each object snap in the expression, one after another.

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The ins and outs of fractional inches in CAL

Using fractional inches in CAL expressions is tricky. If you type 3'2-1/2" as a CAL expression, AutoCAD replies Error: Invalid feet’-inches” format. AutoCAD expects a hyphen only between feet and inches. Otherwise, it assumes a hyphen is a minus sign. To write out fractional inches, think of them as little division problems being added to the whole inches. Therefore, if you type the following expression

(3’2”+1”/2”)+(23”+3”/8”)

61.875

AutoCAD takes 3'2" and adds 1" divided by 2" to get 3'2-1/2". Similarly, in the second expression, AutoCAD adds 23" to 3" divided by 8" to get 23-3/8". Yes, it’s slightly awkward. If 3'-2" returns 38.0, as shown below (3' = 36" and 2 more inches is 38"), how do you subtract 2" from 3'?

>> Expression: 3’-2”

38.0

The trick is to put parentheses around the 3 feet so that AutoCAD doesn’t assume the next expression is part of the same feet-inches expression, as shown here:

>> Expression: (3’)-2”

34.0

Here AutoCAD takes the 3 feet (36") and subtracts 2" to get 34.

	A common use for object snaps in the CAL command is to find the midpoint between two
	points. In Figure 12-14, you want to draw a line starting from the midpoint between the cen-
	ters of two circles.
	To accomplish this, first make sure that OSNAP is off. Then start the LINE command and start
	CAL transparently at the Specify first point: prompt. Follow the prompts:
	>> Expression: (cen+cen)/2
	>> Select entity for CEN snap: Select the first circle.
	>> Select entity for CEN snap: Select the second circle.
	(4.86897 7.73008 0.0)
Tip	You can now use the new Mid Between 2 Points object snap to find the midpoint between
	two points. You can find this object snap on the OSNAP shortcut menu (Shift+right-click). At
	the prompts, specify the two points to immediately find their midpoint. For example, you can
	use this midpoint as the start or end of a line.

To calculate the length of a line, use the abs function. (See the list of mathematical functions in Table 12-3.) The following expression shows how this works:

>>Expression: abs(end-end)

>>Select entity for END snap:

>>Select entity for END snap:

61.0

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First circle

Midpoint between the circles' centers

Second circle

Figure 12-14: Drawing a line from the midpoint between the centers of the two circles.

You can easily use CAL as a substitute for the From object snap. For example, at the Specify first point: prompt you can enter ' cal and type mid+[3,–2.5] . AutoCAD prompts you for the object for which you want the midpoint and starts the line (3,–2.5) units from there.

Using mathematical functions

CAL supports many mathematical functions typical of a scientific calculator. Table 12-3 lists these functions.

Note A real number is any positive or negative number. Type large numbers without commas. AutoCAD restricts you to integers between –32768 and +32767 but real numbers (numbers with decimal places) can be larger.

Table 12-3: CAL Mathematical Functions

Function

What It Does

sin(angle) Calculates the sine of the angle cos(angle) Calculates the cosine of the angle tang(angle) Calculates the tangent of the angle asin(real) Calculates the arc sine of the real number acos(real) Calculates the arc cosine of the real number atan(real) Calculates the arc tangent of the real number

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Function	What It Does
ln(real)	Calculates the natural log of the real number
Log(real)	Calculates the base-10 log of the number
exp(real)	Calculates the natural exponent of the real number
exp10(real)	Calculates the base-10 exponent of the real number
sqr(real)	Calculates the square of the real number
sqrt(real)	Calculates the square root of the real number
abs(real)	Calculates the absolute value of the real number (the number not including its + or
	– sign); also used to calculate lengths
round(real)	Rounds the number to its nearest integer
trunc(real)	Truncates any decimal value leaving only the integer
r2d(angle)	Converts radian angles to degrees
d2r(angle)	Converts degree angles to radians
pi	Returns the constant pi

Using CAL’s special functions

CAL has a set of special functions that you can use to find points. Table 12-4 lists most of these functions and what they do. You can find a complete list in the AutoCAD Command Reference.

	Table 12-4: Special CAL Functions
Function	What It Does
rad	Gets the radius of the selected object
cur	Gets any point that you pick
@	Gets the last point calculated
vec(p1,p2)	Calculates the vector from point p1 to point p2
vec1(p1,p2)	Calculates a one-unit vector from point p1 to point p2
pld(p1,p2,dist)	Calculates a point on the line from point p1 to point p2 that is dist units from
	point p1; if dist is 0.327, calculates the point 0.327 units from p1
plt(p1,p2,t)	Calculates a point on the line from point p1 to point p2 that is t proportion
	from point p1; if t is 0.45, calculates the point 0.45 of the distance from p1 to
	p2 (or almost halfway between them)
dist(p1,p2)	Calculates the distance between point p1 and point p2
dpl(p,p1,p2)	Calculates the distance from point p to the line from point p1 to point p2

Continued

292 Part II Drawing in Two Dimensions

		Table 12-4 (continued)
	Function	What It Does
	ang(p1,p2)	Calculates the angle between the X axis and the line from point p1 to point p2
	ang(v)	Calculates the angle between the X axis and a vector you define; an example
		of a vector would be (end-end) where you pick the two endpoints of a line
	ang(apex,p1,p2)	Calculates the angle between the lines from apex to point p1 and apex to
		point p2; (the apex is the vertex of the angle).
	ill(p1,p2,p3,p4)	Calculates the intersection of two lines from p1 to p2 and from p3 to p4
Note
	A vector is a direction, which is expressed as delta X, delta Y.

Remember that you can specify these points in many ways, most commonly by object snaps. You can use the cur function to pick any point on the screen.

On the	The drawing used in the following Step-by-Step exercise on using the CAL command, ab12-a.
CD-ROM	dwg, is in the Drawings folder on the CD-ROM.

STEP-BY-STEP: Using the CAL Command (AutoCAD Only)

1.Open ab12-a.dwg from the CD-ROM if you don’t have it open from the previous exercise.

2.Save the drawing as ab12-01.dwg in your AutoCAD Bible folder.

3.If you did not do the previous exercise, use ZOOM Window to zoom in on the parcels labeled D and E, as shown in Figure 12-15.

4 5 2

1

3

Figure 12-15: Parcels D and E in the civil engineering drawing.