Pick points quickly with object tracking in AutoCAD 200030 Sep, 2000 By: Bill Fane
AutoCAD 2000 greatly simplifies and extends the object tracking mode introduced in Release 14 (see Learning Curve, May 1999). Object tracking helps you locate points relative to other points in a drawing. Lets turn on the Wayback Machine and go for a brief trip through the history of point selection. In the early releases of AutoCAD, you either typed in a coordinate pair or used an object snap to obtain a new point. A later release added point filtering, which let you snap to a point and then extract just a portion of the coordinate, such as the x, y, or z value or the xy, xz, or yz values. AutoCAD then prompted you for the missing values, which you could also supply by point filtering. This was potentially very useful, but also quite cumbersome.
As indicated in my May 1999 column, Release 14 added object tracking. This simplified the extraction of partial coordinates from a point, but is still a little messy.
AutoCAD 2000 develops object tracking to a fine art.
|Figure 1. The goal is to draw a circle in the center of the hexagon.|
Take a peek at figure 1. Suppose you need to draw a circle right in the center of the hexagon. You could use object snaps to draw a line from the middle of one side to the middle of the opposite side, draw a circle whose center is snapped to the middle of this new line, and then erase the line. Object tracking provides a much faster and easier way, but first you have to set things up.
First, right-click on the Osnap button in the status bar at the bottom of the screen. Next, select Settings in the menu that pops up and make sure that only Endpoint and Midpoint are checked. Select OK.
Now make sure the Osnap and Otrack buttons are selected and start the Circle command.
When AutoCAD asks for a center point, dont pick one. Instead, move the cursor to a point somewhere near the middle of the lower horizontal line until the triangular AutoTrack midpoint symbol appears. Do not click on this point, but simply pause there for a moment until a small plus sign appears.
Object Tracking has now acquired this point, but has not yet fed it to the Circle command.
Next, move the cursor near the upper end of the lower right line. The square AutoTrack endpoint symbol appears. Once again, do not click on this point, but simply pause for a moment until the small plus sign appears.
Once again, Object Tracking has acquired this point but has not fed it to the Circle command. Note that the previous midpoint tracking point is still active as well.
|Figure 2. The dotted vertical line and tooltip mean that AutoCAD extracted the x coordinate from the first tracking point.|
Now move the cursor until it is above the first tracking point. A dotted vertical line and a tooltip appear, as shown in figure 2, to indicate that AutoCAD has extracted the x coordinate from the first tracking point.
Now move the cursor so it is to the left of the second point but not above the first one. Figure 3 shows that AutoCAD shifts to extract the y coordinate from this point instead.
A bit of experimenting reveals that you can automatically shift between figures 2 and 3 simply by moving the cursor.
So what happens if you move the cursor above the first point and to the left of the second? Figure 4 shows that AutoCAD extracts the x and y coordinates as appropriate at the same time.
3. AutoCAD is ready to extract the y coordinate from the second point.||Figure 4. Depending on the cursor position, AutoCAD can extract both coordinates at the same time.|
If you now left-click, you select the intersection of the two dotted lines as the center of the circle.
|Figure 5. Voila! Weve drawn our circle without using any construction lines.|
You can now go back to selecting object tracking points as before. Figure 5 shows a circle whose radius is determined by the y coordinate of the midpoints of the lower and lower right lines. None of this required any construction lines. I needed only two mouse clicks to draw the circle.
Lets look at several significant points regarding object tracking.
you can type in the two letters
6. AutoCAD lets you establish temporary tracking points. You can also
use direct distance entry with object tracking.
TT. Pick a point,
using object tracking if you want, and the little plus sign appears.
This point is not fed to the current command, but is available for
further use as a tracking point.
In figure 6, the dashed
lines show how I located the
TT point at the apparent
intersection of the horizontal and upper right lines, then used DDE to
locate the center of the circle at an exact distance above this point.
The dashed lines are for illustration purposes and do not need to actually
exist in the drawing.
Still not convinced that you should use object tracking?
Take a look at figure
7. Given the top and right side views, I created the front view without
using any construction lines, without using Trim, Extend, or Erase, and
without entering any specific distance values. The view is fully orthographic.
I created all the lines, including the hidden and center lines, by using
object tracking to project all required points over and down from the
two given views.
7. Given the top and side view, you can create the front view using
object tracking only.
If you want to try it yourself, I have made the drawing available.
now for something completely different
By the time you read this, it will probably be autumn. Now is a good time to replace your smoke-detector batteries. When you do, write the date on the outside of the case with a soft, black pencil. Now you can tell at a glance when they were last replaced.
About the Author: Bill Fane
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