154 Part II: Let There Be Lines
To specify feet, you must enter the ' symbol for feet after the number. For example:
6' for 6 feet.
You can enter a dash to separate feet from inches, as architects often do: 6'–6" is 6 feet, 6 inches.
Both the dash and the inch mark are optional when you’re entering coordinates and distances:
6'6" and 6'6 are the same as 6'–6".
If you’re typing a coordinate or distance that contains fractional inches, you must enter a dash — not a space — between the whole number of inches and the fraction:
6'6–1/2 (or 6'–6–1/2) represents 6 feet, 6 1/2 inches.
If all this dashing about confuses you, enter partial inches by using decimals instead:
6'6.5 is the same as 6'6–1/2" to AutoCAD, whether you’re working in Architectural or Engineering units.
Have you ever wanted to check the accuracy (or precision!) of something that’s already drawn? The MEASUREGEOM command is a one-stop shop where you can query drawing objects for distances, angles, areas, and other geometric or locational information about drawing objects. You can find it on the Utilities panel of the Home tab — look for an icon with a yellow ruler.
Grab an object and make it snappy
After you’ve drawn a few objects precisely in a new drawing, the most efficient way to draw more objects with equal precision is to grab specific, geometrically precise points, such as endpoints, midpoints, or quadrants, on the existing objects. Every object type in AutoCAD has at least one of these points, and you can “snap” to them precisely as you draw by using object snaps (osnaps for short by those in the know).
AutoCAD provides two ways of using object snaps:
Object snap overrides: An object snap override is active for a single pick.
Running object snaps: A running object snap stays in effect until you turn it off.
AutoCAD (but not LT) has a suite of object snaps specifically for working in 3D. We cover them fully in Chapter 21, but point them out here because the new 3DOSNAP status bar button is right next to the regular old OSNAP button, and not so easy to distinguish from it. In this section, you use the
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Chapter 7: Preciseliness Is Next to CADliness 155
regular Object Snap button that shows the square with the sunburst at the top-left corner, not the 3D-looking box with the sunburst at the bottom-left corner.
Grabbing points with object snap overrides
Here’s how you draw precise lines by using object snap overrides:
1.Open a drawing containing some geometry.
2.Turn off running object snap mode by clicking the Object Snap button on the status bar until the button appears to be dimmed and <Osnap off> appears in the command window.
Although you can use object snap overrides while running object snaps are enabled, we recommend that you turn off any running object snaps while you’re getting familiar with object snap overrides. After you’ve gotten the hang of each feature separately, you can use them together.
3.Start the LINE command by clicking the Line button on the Ribbon’s Draw panel or typing LINE (or L) and pressing Enter.
AutoCAD prompts you to select the starting point of the line:
Specify first point:
4.Hold down the Shift key, right-click anywhere in the drawing area, and release the Shift key.
The Object Snap menu appears, as shown in Figure 7-3.
5.Choose an Object Snap mode, such as Endpoint, from the object snap menu.
The Object Snap menu disappears, and the command window displays an additional prompt to indicate that you’ve directed AutoCAD to seek out, for example, the endpoints of existing objects:
_endp of:
6.Move the crosshairs slowly around the drawing, pausing over various lines and other objects without clicking yet.
When you move the crosshairs near an object with an endpoint, a colored square icon appears at the endpoint, indicating that AutoCAD can snap to that point. If you stop moving the crosshairs for a moment,
a tooltip displaying the Object Snap mode (for example, Endpoint) appears, to reinforce the idea.
7.Click when the Endpoint object snap square appears on the point you want to snap to.
AutoCAD snaps to the endpoint, which becomes the first point of the new line segment that you’re about to draw. The command line prompts you to select the other endpoint of the new line segment:
Specify next point or [Undo]:
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156 Part II: Let There Be Lines
Figure 7-3: The Object Snap right-click menu.
When you move the crosshairs around the drawing, AutoCAD no longer seeks out endpoints because object snap overrides last for only a single pick. You can use the Object Snap right-click menu again to snap the other end of your new line segment to another point on an existing object.
8.Use the Shift+right-click sequence described in Step 4 to display the Object Snap menu again. Then choose another Object Snap mode, such as Midpoint, from the Object Snap menu.
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Chapter 7: Preciseliness Is Next to CADliness 157
The command line displays an additional prompt indicating that you’ve directed AutoCAD to seek, for example, midpoints of existing objects:
_mid of:
When you move the crosshairs near the midpoint of an object, a colored triangle appears at the snap point. Each object snap type (Endpoint, Midpoint, Intersection, and so on) displays a different symbol. If you stop moving the crosshairs, the tooltip text reminds you what the symbol means. Figure 7-4 shows what the screen looks like during
this step.
Already object-snapped to endpoint
Newline segment
About to object-snap to midpoint
Figure 7-4: A snappy line.
9.Draw additional line segments by picking additional points. Use the Object Snap right-click menu to specify a single object snap type before you pick each point.
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158 Part II: Let There Be Lines
Try the Intersection, Perpendicular, and Nearest object snaps. If your drawing contains arcs or circles, try Center and Quadrant.
10.When you’re finished experimenting with object snap overrides, rightclick anywhere in the drawing area and choose Enter from the menu to end the LINE command.
There’s a difference between right-clicking and Shift+right-clicking in the drawing area:
•Right-clicking: Displays menu options for the current command (or common commands and settings when no command is active).
•Shift+right-clicking: Always displays the same Object Snap menu.
Running with object snaps
Often, you use an object snap setting (such as Endpoint) repeatedly. Use running object snaps to address this need.
The following steps set a running object snap:
1.Right-click the OSNAP button on the status bar.
The Object Snap menu appears, as shown in Figure 7-5.
Many status bar buttons display shortcut menus when you right-click, as shown in Figure 7-5. (Object Snap and Object Snap Tracking both display the menu of running object snaps.) Many settings, including all running Object Snap types, can be set by clicking a menu item — you no longer need to open the Drafting Settings dialog box, make your settings, and then click OK to close the dialog box.
2.Click in the menu to select one or more Object Snap settings.
Active running Object Snap settings show a highlighted square around the icon (see Figure 7-5).
You click the Object Snap button on the status bar to toggle Running Object Snap mode. After you turn on Running Object Snap, AutoCAD hunts for points that correspond to the object snaps you checked on the Object Snap button’s right-click menu. As with object snap overrides, AutoCAD displays a special symbol — such as a square for an Endpoint object snap — to indicate that it has found an object snap point. If you keep the crosshairs still, AutoCAD also displays a tooltip that lists the kind of object snap point.
Use object snap overrides or running object snaps to enforce precision by making sure that new points you pick coincide exactly with points on existing objects. In AutoCAD, it’s not good enough for points to almost coincide or to look like they coincide. You lose points, both figuratively and literally, if you don’t use object snaps or one of the other precision techniques covered in this chapter to enforce precision.
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