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AutoCAD

Circles and Lines: Object Snaps-Part 1

15 Aug, 2004 By: Lynn Allen

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Get the most out of the osnap options.

Object snaps are an integral part of everyday AutoCAD drawing life. Drawing without them would be tedious and inaccurate. But are you using them to their fullest potential? Are you, heaven forbid, taking your object snaps for granted? Do you understand all the object snaps and their complete functionality? Are you using just the ones you think you need?

This month, we'll tour the various object snaps to ensure you're getting the most osnap for your buck! I've had several requests from readers to review some of AutoCAD's basics that many of us take for granted. Here's to listening to you!

Snap Attack

When you use an object snap, also known as an osnap, you simply snap to a specific geometric point on an entity. Object snaps are always accurate and much easier than trying to find the desired point on your own. You can use object snaps anytime you're asked to indicate a point within your drawing. Osnaps don't grab objects that aren't visible or between the dashes of a noncontinuous linetype.

You can use object snaps temporarily or set a persistent running object snap. Now we have the advantage of visual cues with AutoSnaps. Our tour follows 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. The command-line interface is included in parentheses for those of you who still type commands. You're in good company—I'm still an offender.

• 1. Temporary Track Point (Tt). Used in conjunction with object snap tracking (that powerful yet somewhat elusive feature that came out in AutoCAD 2000), Tt sets a temporary tracking point for reference. After you start Tt, the next position you select is marked with a temporary marker. Notice that the AutoTrack alignment paths now display relative to the Tt point. If you don't like the marker position, simply rub it out by moving your cursor back over the Tt point. Object snap tracking is a very powerful tool that most AutoCAD experts consider key to creating speedy drawings.
• 2. From (Fro). One of the few good things to come out of AutoCAD Release 13, From lets you select a point of reference before you select the final point. Many of you use the ID command for this purpose or move the UCS for quick reference. From makes this process much simpler. For example, I want to insert a door symbol four inches from the corner of a room. From the Insertion Point option in the Insert command, I use the From object snap to select the corner of the room. I follow this up with @4<90 (polar coordinates), and my door snaps into place. I can use relative or polar coordinates, but I must use the @ sign. Otherwise, AutoCAD references absolute coordinates. If you want to place a tooling hole two units over and up from an existing part of a drawing, the From object snap is a good choice.

Figure 1. To find the list of object snaps in the cursor menu, hold down the <Shift> key and press the second button (usually the right button) on your input device.

• 1. Midpoint Between 2 Points (Mtp/M2p). This keyboard modifier is a great new addition to AutoCAD 2005. Snatched from the geometric calculator (mee) function, this option lets you grab the midpoint between two points on the screen. I chuckle that there are two ways—Mtp and M2p—to access this great feature. I guess the command-naming spinner landed right on the line between the two!
• 2. Endpoint (End). Use the Endpoint object snap to grab the closest endpoints of objects such as lines, arcs, elliptical arcs, mlines, rays, splines, 3D faces, 3D solids, regions, polylines, and the new table object. EndPoint also snaps to the vertices of polylines that include polygons, rectangles, and so on. End is always a bit faster and more accurate than Intersection (everyone's favorite), and I suggest you use it whenever possible.

Back in AutoCAD's covered wagon days, typing the End command saved your drawings and shut down AutoCAD, no questions asked. It was common to accidentally key in the End osnap at the command line—one minute we were looking for an endpoint and the next we saw the Windows Program Manager. Doh!

• 1. Midpoint (Mid). Mid grabs the midpoint of a line, arc, polyline segment, spline, elliptical arc, region, table cells, or bhatch segment. You can even grab the midpoint of an xline, which by definition should be impossible because xlines go on forever. What exactly is infinity divided by two? AutoCAD selects the location you used to create the xline as the midpoint. Midpoint can also find the midpoint of the sides of some 3D solids. If you've assigned an extrusion thickness to an arc or line, you can snap to the midpoint of the extrusion.

Figure 2. If you use running object snaps, you can tailor them in the Drafting Settings dialog box.

AutoCAD Help claims you can find the midpoint of an ellipse, which incidentally isn't true.

• 1. Center (Cen): Cen snaps to the center of an arc, circle, ellipse, elliptical arc, and some 3D solids.
• 2. Quadrant (Qua): This often forgotten object snap can be quite useful. Use it to snap to the nearest quadrant of an arc, circle, ellipse, elliptical arc, and some 3D solids. When an arc isn't large enough to have a quadrant, you receive an error message.

Rules and Reminders

Object snaps treat polylines, blocks, and tables as individual entities and don't always play nicely with blocks that are not uniformly scaled. You can implement any of these osnaps in two ways: temporary and running. When you pick an osnap from the AutoCAD toolbar or cursor menu, or key it in manually, you're using temporary object snaps that override all other settings. The desired object snap setting is valid for one step, and then it's gone.

Tip. If you have trouble getting to your desired object snap while Autotracking is on, press the <Tab> key to cycle through all possible object snaps.

We weren't able to get through all of the object snaps this month, but will tackle the rest next time. Until then, Happy AutoCAD-ing!