Circles & Lines: Object Snaps, the Sequel

14 Sep, 2004 By: Lynn Allen

Learn more object snap options.

Figure 1. The Osnap cursor menu.
Object snaps in AutoCAD are integral to our everyday drawing life -- without osnaps, our drawings would be filled with inaccuracies. Last month, we tackled about half of the object snaps available ( This month, I'll address the remainder. All you LT users, I hope you've been paying attention, because the last three columns apply to you as well. By the way, the visual cues that help you select the appropriate object snap are called AutoSnaps.

Should you be wondering about my abilities to alphabetize, I'm following the object snaps as they appear in the cursor menu (figure 1), which appears when you hold down the Shift key and press the second button (usually the right button) on your input device. I include the command-line interface in parentheses for those who still type commands. I'm picking up where we left off last month, with the most popular of all the object snaps, Intersection.

The Rest of the Osnaps
Intersection (Int). The Intersection object snap is a very popular tool that grabs imaginary or real intersections. By definition, an intersection is where one or more objects cross. An imaginary intersection is where one or more objects would cross if extended in the same direction. Years ago, Autodesk modified the Int object snap to accept these imaginary extended intersections.

The Int osnap contains one additional modification -- the ability to select two objects, one at a time, so AutoCAD can find their intersection. When the osnap aperture doesn't find an actual intersection after the first pick, it prompts you for another object. This feature is great when you find it difficult to get into tight places.

Though some of you are Intersection junkies, others might take issue with this feature when you realize AutoCAD needs just a smidgen (technical term of measurement) more time than usual to calculate the intersection algorithm, so it might not be the fastest object snap. To grab corners, I strongly recommend you use the faster and easier Endpoint object snap. Although Int works in this instance, it's only accurate to a certain degree, so I suggest you use this option only when no other object snap will do. If you've ever tried to trim objects that you constructed using Int and were told you couldn't because there was no true intersection, Int is to blame.

Apparent Intersection (Appint). Appint is extremely important for 3D users. The Apparent Intersection object snap lets you snap to two objects that intersect in the current viewing plane, though they don't actually meet in 3D space. Appint works just like the Int object snap, but the objects must cross or meet in the current viewing plane. Appint also graciously extends the objects to an imaginary intersection. You also can select the objects individually, as for the Int object snap.

Tangent (Tan). Use the tangent osnap to snap to the tangent of an object. As with Perpendicular, you usually select a reference first. To create a circle tangent to three lines, you can use the Tan osnap combined with the 3P option in the Circle command. Perpendicular and Tangent won't let you break any rules of geometry. Deferred Tangent Snap mode displays when the object you are drawing requires more than one tangent snap.

Perpendicular (Per). Use Per to snap to a point perpendicular to the selected object. Usually, you select a reference point first. You can snap perpendicular to most 2D geometry and some 3D. AutoCAD automatically turns on a Deferred Perpendicular Snap mode when the object you are drawing requires more than one perpendicular snap, such as perpendicular lines between objects.

Parallel (Par). This fairly new object snap makes it easy to draw a vector parallel to an existing object. After designating the first point, simply move the cursor over the straight-line segment of an existing object. This acquires the information needed to position the second point. A parallel alignment path displays, making it easy to select the second point.

Node (Nod). Use this to snap to points created using the Point command. Points can prove invaluable in the Divide and Measure commands, where snapping to them is the next logical step. Be sure to set PDMODE to a decent value -- 3, for example -- to ensure you can actually see your points. You can find the Point Style dialog box in the Format pull-down menu. Node also snaps to dimension defpoints and dimension text origins.

Insert (Ins). Use this object snap to snap to the insertion point of text, a block, an attribute, or the new fields. You can also snap to the nearly extinct shapes in past releases. This option can be very useful when you want to add another line of text directly below an existing text string while maintaining consistent spacing. Using the Dtext command, snap to the insertion point of the existing text. When prompted for the new text string, you'll notice the Dtext box residing on the previous line of text. Press the space bar (so AutoCAD records something other than null input) and press an extra Enter to drop to the next line. Your new text string lines up directly with the previous string of text.

Nearest (Nea). Use Nea to snap to the nearest point of just about any AutoCAD object. Nearest doesn't like text or attributes. It's defined by the point closest to the center of the aperture.

None (Non). Ever have a running object snap that was getting in your way for one or two quick operations? Did you turn off your running osnap completely, then turn it back on when you completed those operations? If so, you're doing too much work. The None object snap turns off the running object snap for one operation only.

Make it Yours
You can further customize your object snap behavior in the Drafting tab of the Options dialog box (figure 2).

Figure 2. Customize your object snap behavior in the Drafting tab of the Options dialog box.

I strongly suggest you keep Marker, Magnet, and Display AutoSnap Tooltip selected. This ensures that AutoCAD displays the AutoSnap markers that indicate which object snap you're grabbing, a helpful tooltip (useful until you've memorized all the symbols), and the magnet properties that pull you into the proper position. Most of us no longer use the AutoSnap aperture box because the new visual cues just seem to work so much better. But I'm sure a few of you veterans out there still refuse to part with it!

You can easily adjust the size and color of your AutoSnap markers in the Options dialog box. Blue is so difficult to see on a black background that many have changed it to an easier-to-view color such as green or yellow. Ignore Hatch Objects is new to AutoCAD 2005. This feature removes the irritation that occurs when AutoCAD insists on snapping to every vector in a crosshatch pattern. This sets the new OSNAPHATCH system variable -- as if we need any more system variables!

I hope at least one of these object snap explanations will help you improve your productivity. Next month I'm going to raise the bar and move back to some more advanced features in AutoCAD. Until then, Happy AutoCAD-ing!

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