AutoCAD 2000's Parallel and Extend options

1 Nov, 2000 By: Bill Fane

Captain LearnCurve thought about the tracks he had seen during a recent motorcycle ride. Deer tracks were quite common, and he'd even spotted a few bear tracks. The easiest tracks to identify, however, were those left by a train. This is another terrible lead-in to this month's topic, isn't it? Now that you mention it, the reference to railroad tracks does give me an idea for a topic. Railroad tracks are parallel, so I'll discuss the new parallel object snap in AutoCAD 2000. AutoCAD 2000's new Parallel object snap “draws a vector parallel to another object whenever AutoCAD prompts you for the second point of a vector,” according to the product documentation.

Figure 1 (right). With the Parallel object snap active, simply pause on a line to select it as the “parallel to” definition.

Playing with Parallel

First draw the longer diagonal line shown in figure 1. Then right-click the Osnap button, select Settings, and activate Parallel. You now have a parallel running object snap active, along with any other object snaps that are set.

Next, start a new line near point A. When AutoCAD asks for the next point, simply move the cursor close to the first line. After you pause there for a moment, AutoSnap acquires the line and applies the Parallel object snap. It displays the parallel symbol and the yellow tooltip box. AutoSnap symbols normally display in yellow, but they are changed to green in the figures so they show up better in the magazine.

Note that you don't click on the first line at this point, but merely pause there until the AutoSnap symbol appears.

As you move the cursor away from the first line, everything reverts to normal operation except that a small cross remains on the first line to indicate that a snap mode is active.

Figure 2 shows what happens as you continue to move the cursor. When the cursor is nearly parallel to the first line, the rubber-band image of the new line snaps to being parallel with the first line. The AutoSnap symbol reappears on the first line, the tooltip box appears to indicate the object snap mode that applies, and the rubber-band line extends from each end in a dotted format to indicate the parallel vector.

Figure 2. When you move the cursor until the rubber band is nearly parallel to the first line, it snaps over and becomes exactly parallel.

Figure 3. Pick a point, and the new line segment is parallel to the existing one.

When you pick a point under these conditions, AutoCAD draws a new line segment parallel to the first line, as shown in figure 3.

Can't I use the Offset command to do that?

Figure 4. Given point B and line CD . . .

Not quite. When you offset a line, it makes an exact copy offset from the first. In the current example the new line is a different length from the original. Offset also requires you to know the offset distance, which you can type in directly or indicate by picking two points.

In figure 4 (right), the goal is to draw a line that starts at end B of the lower line and is parallel to line CD. With Parallel and Endpoint running object snaps active, all you need to do is start the line near end B (it snaps to the endpoint of the line), then briefly park the cursor on line CD to activate the Parallel snap.

When you move the cursor as shown in figure 5 (below), the rubber-band line snaps to an orientation that is parallel to the line CD. When you pick a point, you get the result shown in figure 6 (below). All of this required only two mouse picks. You don't need to know the offset distance, use any construction lines, do any trimming, or erase anything.

Figure 5. . . . I can use the Parallel object snap to draw a line that . . .

Figure 6. . . . starts at point B and is parallel to CD.

This is starting to sound remarkably similar to your last two columns, on polar mode and object tracking!

By an amazing coincidence, they all work together and in much the same manner. Not only that, but Parallel snap also works with DDE (Direct Distance Entry). In figure 5, suppose you want the new line segment to be an exact length. You can use Parallel to establish the direction and then simply type in a value for the new line segment length.

Extend yourself

But wait! There's more! AutoCAD 2000 also adds the new Extend object snap.

Figure 7 below shows an existing line and a new one being started near point E.

With the Extend running object snap turned on, simply move the cursor near the end of the first line. Don't pick this point, but just pause long enough for AutoCAD to acquire the line. You don't need the Endpoint object snap to be on.

Figure 7. Given a line, and a point E . . .

Figure 8. . . . you can draw a line from point E that ends on the extended projection of the first line.

Figure 8 above shows what happens when you move the cursor until it is close to the theoretical extension of the selected line. A dotted line appears to show the extension of the first line. You can slide the cursor back and forth along this line, from upper left to lower right. When you finally pick a point, the new line segment terminates exactly on the theoretical extension of the first line.

Figure 9. Using the Parallel and Extend snap options, you can draw the lower profile with only four mouse picks. All four dotted line segments are collinear with or parallel to their counterparts in the upper profile.

Extend and Parallel can work very well together. Start with the upper solid-line profile in figure 9. Using Parallel and Extension, you can draw the lower dashed-line profile with only four mouse picks. All lines in the lower profile are parallel to or colinear with their counterparts in the upper figure.

Snap judgments
And now for some thought-provoking thoughts on Parallel and Extend snaps. Although all the examples discussed here use running object snap modes, nothing prevents you from applying them as single snap overrides.

Parallel must have a current “From point” selected before you can select an object to which your new vector will be parallel. In many respects, Parallel and Extend behave more like object tracking than like traditional object snaps. For example, you can select several lines as parallel to and/or extended. As you move the cursor, your rubber-band segment jumps around and locks on to the selected line that is most appropriate. Object tracking need not be active.

As with object tracking, you can unselect a paralleled or extended object simply by parking briefly on its marker cross.

You can select several Extend lines and then find the intersection point between any two of them, but you can only be parallel to one at a time.

You are not restricted to lines when determining parallel or extension directions. Polyline segments work equally well.

And now here is the big one. All these examples use lines, and the AutoCAD Help facility refers to vectors, which implies lines. The truth is that these two new object snaps work equally well with any command that asks for point input. You can move objects in a direction that is parallel to an existing line, or you can copy a circle so its center lands on the extension of an existing line, and so on.

The combination of polar mode, object tracking, and the two new object snaps are revolutionizing how we use AutoCAD.

And now for something completely different
If you normally use a cordless telephone, make sure you also have a regular one available. A cordless phone won't work during a power outage, or if you leave it off its base so long that the battery dies.

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