When you draw in AutoCAD or AutoCAD LT, you draw in undefined units. A line from point 3,0 to point 6,0 is three units long. While you're drawing, these units can be anything — a millimeter, a centimeter, a meter, an inch, a foot, or a mile. In reality, you should know exactly what the units represent. After all, you don't want your 36-foot-wide house to end up 36 inches wide!

When you set up a drawing, you specify how units are displayed — for example, whether partial units show as decimal points or fractions. (I cover units in Chapter 5.) However, you don't actually specify what the units represent until you print or plot your drawing — covered in Chapter 17.

To ensure accuracy, you should draw full size. If you're drawing a plan for a factory that will be 120 feet long, for example, you create lines with those measurements. On the screen, you can zoom in to see small details or zoom out to see the whole factory, so that you have no reason not to use the actual line lengths. It's only when you need to print those 120-foot-long lines on a real sheet of paper that you have to specify how to plot out your drawing at a reduced scale.

Users are typically familiar only with the type of notation used in their own field of specialty, whether scientific, architectural, engineering, or whatever. However, you should be at least somewhat familiar with all the major forms of measurement notation.

Dynamic Input enables you to enter text input near the cursor. In Chapter 3, I explain how to use the Dynamic Input tooltip for commands and command options. Here I explain how to use it to enter coordinates.

Typing coordinates in the Dynamic Input tooltip

You can type 2D coordinates in the Dynamic Input tooltip in the same way that you type them on the command line — in the format x,y. You can press Tab between the X and Y coordinates instead of typing a comma, but typing the comma is probably easier and therefore more accurate.

When you draw a line, after you specify the first point, you see only one tooltip box because AutoCAD assumes that you want to enter only the distance, using the current angle of the temporary line shown on the screen. However, as soon as you type a comma or press the Tab key, a second box appears so that you can enter the Y coordinate, as shown in Figure 4.2. The same situation applies when you want to move or copy an object and want to specify an X,Y displacement.

In Figure 4.2, note the lock next to the X coordinate. Before you type any part of the coordinate, both the X and Y values vary as you move the mouse. When you enter a value for the X coordinate, you fix this value, as the lock indicates. However, the Y coordinate is still unlocked until you type a value.

Figure 4.2. As you enter an X,Y coordinate, two boxes appear, one for each part of the coordinate.

Specifying Dynamic Input settings

You can specify how Dynamic Input works for coordinates that you type. Changing the settings gives you very different results when you type coordinates, so you should familiarize yourself with the settings. To specify settings for the Dynamic Input feature, right-click the Dynamic Input button on the status bar and choose Settings to display the Dynamic Input tab of the Drafting Settings dialog box, as shown in Figure 4.3.

Figure 4.3. Use the Dynamic Input tab of the Drafting Settings dialog box to specify how your Dynamic Input works when you type coordinates.

Pointer Input section

The Enable Pointer Input check box is selected by default, which means that the Dynamic Input tooltip includes an input box where you can type coordinates at the start of any command. If you uncheck this check box, you see these first coordinates only on the command line as you enter them. However, whether the check box is checked or not, as long as the Dynamic Input button is selected on the status bar, you see the input box for subsequent coordinates in a command. For example, if you are drawing a line, and the Enable Pointer Input check box is not checked, you don't see coordinates that you type for the start point in the Dynamic Input tooltip, but for the next point, you see the input box and coordinates that you type appear in that box.

Click the Settings button to open the Pointer Input Settings dialog box. Here you can make the following choices:

• Default format for second or next points. You can choose to default to polar or Cartesian format. The default is polar format, which shows distances. I explain polar format in the "Polar coordinates" section, later in this chapter. You can also choose between relative and absolute coordinates, as shown in Figure 4.4. The default is relative coordinates, which indicate a distance and direction from a previously specified point. I explain both absolute and relative formats in the next few sections of this chapter.

• Tooltip visibility. You can specify that you see the tooltip only when you start typing a point in response to a prompt, automatically at a prompt for a point (the default), or always.

Figure 4.4. The Pointer Input Settings dialog box sets important options for Dynamic Input.

Warning

The settings in this dialog box are very important for determining how all of your coordinate entries work when Dynamic Entry is turned on. If you are upgrading from an earlier version of AutoCAD, you are used to the entry of X,Y coordinates denoting absolute, not relative, coordinates. However, with Dynamic Input turned on, the default is relative coordinates. This is a great default and will speed up your coordinate entry, but can be very confusing if you are unaware of this setting or where to change it.

Dimension Input section

The Enable Dimension Input Where Possible check box is selected by default. This section has nothing to do with dimensions! Instead, it refers to distances or lengths as well as angles, as opposed to points or coordinates. With this check box selected, after you indicate a first point, such as the start of a line or the center of a circle, you see a dimension tooltip that shows the length of the line segment or radius of the circle, as shown in Figure 4.5. You specify the length by typing in this tooltip. If you uncheck the check box, you don't see this dimension tooltip.

Figure 4.5. The so-called dimension input tooltip shows distances and angles.

Click the Settings button in this section of the dialog box to open the Dimension Input Settings dialog box. Here you can change settings relating to dimension input during grip editing. I discuss grip editing in Chapter 10.

Note

If you uncheck both the Enable Pointer Input and the Enable Dimension Input Where Possible check boxes, you turn off Dynamic Input.

Dynamic prompts section

The Show Command Prompting and Command Input Near the Crosshairs check box enables the display of command prompts and your input in response to these prompts in the Dynamic Input tooltip. This part of Dynamic Input is supposed to take the place of the command line. However, the prompts are not an exact echo of what you see on the command line, and certain prompts do not appear in the tooltip.

Note

If you like Dynamic Input, try turning off the command line by using the COMMANDLINEHIDE command or by pressing Ctrl+9. You can get the command-line window back with the COMMANDLINE command or by pressing Ctrl+9 again. You can also undock the Command Line window, right-click its title bar, and choose Auto-hide. Then the Command Line window collapses to just its title bar; when you place the cursor over it, it automatically expands again.

Click the Drafting Tooltip Appearance button to open the Tooltip Appearance dialog box. Here you can change the color of the tooltip, change its size and transparency, and apply the settings to all drafting tooltips in AutoCAD.

When you type a line and enter the actual coordinates, such as a line from point 3,2 to 6,9, you are using absolute Cartesian coordinates. Absolute coordinates are measured from 0,0.

If you have Dynamic Input on with the default setting of relative units, you must enter the # symbol before entering the X portion of an absolute Cartesian coordinate when specifying the second or next point, as explained in the previous section. In this exercise, you practice entering absolute Cartesian coordinates.

STEPS: Entering Absolute Cartesian Coordinates

You can now see that you've drawn a simple window, as shown in Figure 4.6.

Two questions may have occurred to you during this exercise. First, isn't there a better way of entering absolute coordinates? Typing them in is slow and prone to error. Second, how do you know the absolute coordinates for what you're drawing? Read on for the answers.

Figure 4.6. A window drawn with absolute coordinates.

In practice, you usually don't know the absolute coordinates of the points you need to specify in order to draw an object. Whether you're drawing an architectural layout, a physical object (as in mechanical drawing), or an electrical schematic, you don't have X,Y coordinates from which you can work. However, you often do have the measurements of what you're drawing. Usually, you start from any suitable point and work from there. In this situation, you know only the length of the lines you're drawing (if you're drawing lines). Real life doesn't have a 0,0 point. Relative coordinates were developed for these situations.

Relative coordinates specify the X and Y distance from a previous point. They are called relative coordinates because they have meaning relative only to a point previously specified. Suppose that you need to draw a window. You can start the window from any point. From there, you have the measurements you need.

If you have Dynamic Input on — set to the default option of relative units — X,Y coordinates are automatically relative. If you have Dynamic Input off or have set Dynamic Input to absolute coordinates, as described earlier in this chapter, you specify that the coordinates are relative by using the @ symbol. For example, if you start a line by picking any point with the mouse, and you know it should be two units long, you can specify the next point as @2,0. The result is a line starting with the first point you picked and ending two units along the X axis, as shown in Figure 4.7. The line is horizontal because the Y coordinate is 0. In a relative coordinate, this means that the Y distance does not change.

Relative Cartesian coordinates are often used for lines drawn at 90-degree angles (that is, they are either horizontal or vertical). These are called orthogonal lines. However, when you create a diagonal line from point 3,3 to point @2,5, the length of the line is not immediately obvious.

Figure 4.7. A line whose start point could be anywhere and whose endpoint is specified with the relative point @2,0 is a horizontal line two units long.

When you specify a positive number, such as the 2 in @2,0, the direction is positive. If you want to draw a line in the negative direction of an axis, type a minus sign before the number. Figure 4.8 shows how to draw lines in four directions, using relative coordinates.

Figure 4.8. Drawing lines in the four orthogonal directions with relative coordinates. The arrow on each line shows the direction of the line.

Another common situation is to know the distance and angle of a point from either 0,0 or a previous point. In this case, you can use polar coordinates, which can be either absolute or relative. Most commonly, you use relative polar coordinates.

Polar coordinates take the form distance<angle. (To type the angle symbol, use the less-than symbol on your keyboard.) If you have Dynamic Input on, set to the default options of relative coordinates, polar coordinates are automatically relative. If you have Dynamic Input off or have set Dynamic Input to absolute coordinates, as described earlier in this chapter, you need to add the @ sign before a relative polar coordinate. If you also have the default option of polar format selected, you first see coordinates in polar format. Enter the distance, press the Tab key, and then enter the angle. You can also type the angle (<) symbol instead of using the Tab key. To switch to Cartesian format, just type a comma between the X and Y coordinates.

With Dynamic Input on, angles are measured from 0 to 180, with 0 to the right, going either clockwise or counterclockwise. Watch the dotted lines near the angle's tooltip to see exactly what the angle shown in the tooltip is measuring. You can use negative angles. With Dynamic Input off, angles are measured counterclockwise, with 0 to the right, ranging from 0 to 360.

In the following series of steps, you draw part of a portico, the decorative molding above a door or window. You'll use architectural units. In this case, only inches are used, which don't need to be specified. You can specify feet by using an apostrophe (also called a prime) after any number.

When typing architectural units, partial inches are indicated by fractions in the form a/b. You need to separate the fraction from the whole inches by a hyphen. This can be a little confusing because the hyphen is also used for negative numbers. For example, to draw a horizontal line of 5¼ inches in the negative direction of the X axis, you would type -5-1/4,0. (The 0 indicates no change in the Y axis because it is a horizontal line.)

STEPS: Using Relative and Polar Coordinates

Tip

You can type @

Notice that using relative coordinates, both Cartesian and polar, is much more realistic than using absolute coordinates. However, typing in coordinates is still awkward. Typing in coordinates is often the only way to get exactly what you want. Nevertheless, several other techniques for specifying coordinates are easier in many circumstances. I discuss these techniques in the next few sections.

One shortcut for entering coordinates is direct distance entry. After you specify the start point of a line, at the Specify next point or [Undo]: prompt, simply move the mouse cursor in the direction you want the line to go and type in the line's length. It works best in orthogonal mode or with polar tracking (discussed in the following section), which makes specifying the exact angle easy.

Lines drawn at 0, 90, 180, and 270 degrees are called orthogonal lines. When in orthogonal mode — ortho for short — you can only draw orthogonal lines with the mouse. Ortho Mode also affects editing. For example, with Ortho Mode on, you can move objects only vertically or horizontally. Combined with snap and grid, Ortho Mode makes drawing easier and more efficient. Ortho Mode is also great for direct distance entry.

Polar tracking guides you, using a tooltip and vector line, when you want to draw (or edit) at an angle other than the four orthogonal angles, as shown in Figure 4.10. You can use polar tracking for orthogonal angles as well. If you have Dynamic Input on, just look for the word "Polar" to distinguish between the Dynamic Input and the polar tooltips.

Figure 4.10. When polar tracking is on, a tooltip appears when you move the cursor close to one of the polar angles. Here you see a tooltip indicating an angle of 45 degrees.

Polar tracking makes it easy to use direct distance entry to specify distances for many angles. To use polar tracking, you first set the angles that you want to use.

Setting polar tracking angles

To set polar tracking, you can define two types of angles:

• Increment angle. To set the increment angle, click the Increment Angle drop-down arrow, where you can pick from angles that range from every 90 degrees to every 5 degrees. You can also type your own incremental angle in the text box. Polar tracking will then apply to that angle and its multiples.

• Additional angles. If you think that you'll need other angles, check Additional Angles, click New, and then type in an angle. You can add up to ten angles. Note that additional angles are not incremental angles — if you type 35, only 35 degrees will be marked, not 70 degrees or other multiples of 35. To delete an additional angle, select it and click Delete.

Figure 4.11. The Polar Tracking tab of the Drafting Settings dialog box.

To customize how polar tracking works, click Options in the Drafting Settings dialog box to open the Options dialog box with the Drafting tab on top. The following settings in the AutoTracking Settings section apply to polar tracking:

• Display polar tracking vector turns on and off the polar tracking vector, which is the faint dotted line that extends to the end of the screen.

• Display AutoTrack tooltip turns on and off the tooltip that tells you the distance and angle.

The SNAP command is often an alternative to tedious entry of coordinates. This command restricts the cursor to an incremental distance that you choose, such as 0.5 units. You can set the snap size to anything you want. For example, if all your measurements are rounded off to the nearest 0.25 units, you can set your snap to 0.25.

The snap technique is not very useful when you need to draw to three or more decimal places of accuracy. And when you're zoomed out in a large drawing, the snap points may be so close together that you cannot easily find the one you want. But in the right situation, snap is one of the quickest, most accurate drawing techniques available. AutoCAD and AutoCAD LT provide two types of snap settings, Grid Snap and PolarSnap.

Snapping to a grid

When you snap to a grid, an invisible grid becomes active (which you can make visible by using the GRID command, discussed in the next section). As soon as you turn on Grid Snap, the mouse cursor can move only to the Grid Snap points.

Figure 4.15. The Snap and Grid tab of the Drafting Settings dialog box. (The AutoCAD LT dialog box is slightly different.)

Note

In Chapter 8, I discuss rotating the angle of the snap and grid. Chapter 8 also discusses Isometric snap, used for isometric drawing.

Usually you want the X spacing (going across) to be the same as the Y spacing (going up and down). By default, the Equal X and Y Spacing check box is selected, so you need to specify only the X spacing; the Y spacing changes automatically to equal the X spacing. X and Y spacing will be different only if you type a different number in the Snap Y Spacing text box.

The grid

Some users find the grid annoying, but when you first start to use AutoCAD or AutoCAD LT, you may find it helpful. Even accomplished users can take advantage of the grid, especially when starting a new drawing.

Tip

If you're working with a small snap spacing and the dot grid is too dense, set the dot grid to two or more times the size of the snap spacing.

As with the snap feature, you usually want the X spacing (going across) to be the same as the Y spacing (going up and down). You only need to specify the X spacing; the Y spacing automatically changes to be the same, as long as the Equal X and Y Spacing check box is selected in the Drafting Settings dialog box. X and Y spacing will only be different if you type a different number in the Grid Y Spacing text box.

You can turn on the grid in this dialog box by clicking the Grid On check box, but it's easier to click Grid Display on the status bar (or press F7).

In the following exercise, you practice using PolarSnap and Grid Snap points as well as grid dots.

Figure 4.16. A portion of a drawing with the grid turned on and set to 6 inches.

Note

The drawing used in the following exercise on using snap points and grid dots, ab04-b.dwg, is in the Drawings folder on the DVD.

STEPS: Using Snap Points and Grid Dots

1. Open ab04-b.dwg from the DVD. Close any palettes that may be open.

2. Save the drawing in your AutoCAD Bible folder as ab04-04.dwg.

3. 

4. In the Snap Spacing section, the Snap X Spacing should be 0.5.

5. In the Grid Spacing section, the Equal X and Y Spacing check box should be selected. The Grid X Spacing should be 0.5. Click OK.

6. On the status bar, click Snap Mode, Grid Display, and Ortho Mode. The grid appears. Make sure that the Object Snap and Object Snap Tracking buttons on the status bar are off.

7. Choose View tab

   

8. Move the mouse around and watch the coordinates on the status bar. (Right-click the coordinate and choose Absolute if they are in static mode.) They show halves of units because you have set the snap to 0.5.

9. Choose Home tab

   

10. Move the mouse around and watch the coordinates. If you don't see polar coordinates (for example, 3.0000<0), right-click the coordinates and choose Relative.

11. Move the mouse to the right until the coordinates read 8.5000<0 and click. You have drawn a horizontal line with a length of 8.5 units.

12. Right-click and choose Enter to end the LINE command.

13. Move the mouse cursor away from the end of the new line and back to it again, and the absolute coordinates appear. They should be 10.5000,2.0000.

14. Right-click and choose Repeat LINE to start the LINE command again. Use the coordinate display to start the line at 1.5000,1.5000. (For the rest of this exercise, ignore the Dynamic Input tooltip.) Continue to pick points (rather than type them) and draw the following line segments, as shown in the coordinate display:

    0.5000<0
    3.0000<90
    0.5000<180
    3.0000<270

15. End the LINE command.

16. Start the LINE command and pick points, drawing the following line segments (as shown in the coordinate display) starting from 10.5000,1.50. Then end the LINE command:

    0.5000<0
    3.0000<90
    0.5000<180
    3.0000<270

17. Starting from 2.0000,4.0000 draw an 8.5-unit line at 0 degrees. End the LINE command.

18. Start the LINE command again. At the first prompt, pick 11.0000,2.0000. Right-click the Snap Mode button on the status bar and choose Settings. In the Snap Type section, choose PolarSnap. (This is equivalent to choosing the PolarSnap On feature on the Snap Mode button's shortcut menu.) In the Polar Spacing section, change the Polar Distance to 0.5. Choose the Polar Tracking tab and set the Increment Angle to 45 degrees. Click OK. Click Polar Tracking on the status bar.

19. Move the cursor in a 45-degree direction from 11.0000,2.0000 until you see the tooltip. Move along the polar tracking vector until the tooltip says 3.5000 < 45° and click. End the LINE command.

20. Right-click the Snap Mode button and choose Grid Snap On. Start the LINE command and, at the Specify first point: prompt, choose 11.0000,4.0000.

21. Right-click the Snap Mode button and choose PolarSnap On. Move the cursor in a 45-degree direction until the tooltip says 3.5000 < 45° and click. End the LINE command.

22. Save your drawing. Your drawing should look like Figure 4.17.

As you no doubt experienced, this is a much easier way to draw compared to typing in coordinates. Note that drawing with Snap on works better when you're drawing small objects. However, even when drawing an office building, you spend a great deal of time working on small details that may be easier to draw with Snap on.

Figure 4.17. The completed pipe section.

Often you need to draw relative to an existing object. For example, you may need to start a line from the endpoint or midpoint of an existing line. Object snaps (OSNAPS for short) enable you to precisely specify a point by snapping to a geometrically defined coordinate on an existing object. Object Snaps provide a very precise and efficient way to draw.

Here are three ways to specify an object snap:

When you specify an object snap, a prompt for that object snap appears on the command line. For example, if you choose a midpoint object snap, you see mid of on the command line. Unfortunately, the Dynamic Input tooltip does not show this prompt.

Table 4.1 lists the object snaps. Use the abbreviation to type the object snap from the keyboard.

When drawing a line, think of it as having a starting point and an ending point. After the line is drawn, however, both of these points are considered endpoints in terms of object snaps. When picking the endpoint of a line for the endpoint object snap, pick a point on the line closer to the endpoint that you want. The same applies to arcs. Although the arc prompts read Start point and End, both are considered endpoints for purposes of object snaps.

AutoSnap is a feature that helps you work with object snaps. When you move the cursor near the geometric point you have specified, such as an endpoint, you are notified in three ways:

Figure 4.18 shows an endpoint marker and AutoSnap tooltip.

Figure 4.18. AutoSnap shows you the endpoint of the line.

You can customize the AutoSnap feature to suit your needs or make it go away completely if you want. Choose Application Button

In the following exercise, you practice using object snaps.

STEPS: Using Object Snaps

The Endpoint object snap is probably the most commonly used of all the object snaps. It would be nice to have a method of using object snaps that you use often without resorting to a menu, toolbar, or keyboard entry. The solution is to set a running object snap, which keeps one or more object snaps on until you turn them off.

You use the Object Snap button on the status bar to turn on your running object snaps. If you want to turn them off temporarily, just click the Object Snap button or press F3. This capability to toggle running object snaps on and off makes it easy to work with running object snaps on almost all the time, because you can turn them off at the click of a button.

Figure 4.21. Use the Object Snap tab of the Drafting Settings dialog box to set running object snaps.

To start using object snap tracking, at least one object snap must be active. Turn on a running object snap, as explained in the previous sections. Then click the Object Snap Tracking button on the status bar.

With object snap tracking on, follow these steps:

After you acquire a point, you can clear it in any one of three ways:

You can customize the following features of object snap tracking on the Drafting tab of the Options dialog box (choose Application Button

In the following exercise, you practice locating points with object snap tracking.

STEPS: Locating Points with Object Snap Tracking

Figure 4.26. The completed drawing.

The temporary tracking feature is similar to object snap tracking, but limits you to horizontal and vertical directions. Follow these steps:

The cursor moves to the intersection of the vertical and horizontal rubber-band lines. You can now continue your command.

Point filters enable you to specify a coordinate by using the X coordinate of one existing object snap and the Y coordinate of another. You construct an X,Y coordinate based on coordinates of existing objects. If this sounds complicated, it is. Object snap tracking should mostly eliminate the need to go back to the old point filter way of doing things. (Point filters have been around for a long time.)

Here's how to use point filters:

The From feature enables you to create a new object starting at a known distance and direction from an existing object. It's like creating one or more invisible lines between the existing object and the new object, helping you to start the new object in the proper place. Use the From feature when the point you need to specify is a known X,Y distance from an object snap but not on any object snap itself. Here's how to use the From feature:

In the following exercise, you practice using the From feature.

STEPS: Using the From Feature

Figure 4.28. The completed steam boiler.