AutoCAD

Isn't that spatial?

1 Nov, 2002 By: Bill Fane


These are the voyages of the cadship EnterGeek, Captain LearnCurve commanding. Her one- column mission: to explore new AutoCAD commands, to seek out new functionality, to boldly go where the documentation has never gone before. Captain's log stardate (rtos (getvar "cdate")) = "20020908.1708". Cadfleet Command has received reports of interesting new dimensional objects. Our mission is to make first contact and see if these new objects are worthy of joining the CadUser's Federation. Mr.Sulu, lay in a course for quadrant 2002 of the AutoCAD universe.

Aye, aye, Captain!

We have been traveling for some time now in layout mode (paper space) at Warped Factor 5.

Captain, sensors report an opening in the time-space continuum of Layout mode.

What sort of opening, Mr. Spock?

It seems to be a wormhole bridging into a parallel universe, a viewport if you will. It allows us to look into model space.

We have seen those before, in many earlier quadrants.

This one has a dimension in it that reaches through the viewport to an object in model space.

Again, we have seen those before.

This one seems to behave differently.

Perhaps this is what we have been seeking! Continue to monitor it, and report regularly.

Fascinating. Unlike the earlier ones, it includes tractor beams that lock onto the model space object. If the model space object moves or changes size, the dimension in Layout mode moves and changes value to match.

I believe we've found what we're looking for. Set the laser printer on Stupefy and prepare an away party.

The tricorder readings indicate that this Dimension object is directly attached to the model space object. It seems to have evolved into a higher form of dimension that no longer needs Defpoints to define its attachment to the object.

Let's start by analyzing the findings of the away team, then come back to look at the new dimension objects in layout mode.

AutoCAD 2002 now uses true associative dimensions. In earlier releases, each dimension object included a definition point (defpoint) at the end of each extension line to anchor the dimension and to define its length. If you stretched a line, its related dimension changed to reflect the new line length.

Actually, this was a cunning hoax because the dimension was not really related to the line. To change the length of a line, you had to use the Stretch command and make sure the crossing window also picked up the defpoint. The line and the dimension actually changed independently of each other, and the dimension updated to match the new defpoint location.

Figure 1. Draw some objects, and
dimension them.

Figure 2. Click on the circle to invoke
grip editing.
Figure 3. Dimensions update automatically when you edit objects.
Figure 4. Multiple dimensions can update after a single edit.

With true associative dimensions, the dimension object actually "knows" the object or objects to which it is attached. If you edit the host object, the dimension automatically follows. Try it. Draw a line, a circle, an arc, and two lines, then apply dimensions as shown in figure 1.

At the Command prompt, click on the circle to invoke grip editing (figure 2).

Click on the blue box at the center of the circle, move it to a new location, and click to drop it.

Next, click on one of the four blue boxes at the quadrant points, move it to a new location, and click to drop it and revise the circle diameter.

Try the same thing with the arc, the ends of the single line, and the outer ends of the pair of lines.

Magic! At each step, the dimension automatically follows and updates, as shown in figure 3.

Now try this. Add a vertical dimension to the single line. Click on Modify | Properties to bring up the Properties dialog box, then click on the line so its properties show in the box.

Edit the Start x, Start y, End x, and End y values. As you do so, the line and dimensions update (figure 4).

Captain, given their sticky nature, would you call them Klingon dimensions?

My standards are much higher than that. I would never use such a cheap gag.

You must exercise a bit of care when editing. If you move the end of one of the extension lines, that end loses its associativity.

Bones here, Captain. I think I can heal it.

Simply click Dimension | Reassociate Dimensions to invoke the Dimreassociate command. When prompted, select one or more dimensions.

Figure 5. The blue X indicates an unattached dimension.
Figure 6. The blue box around the X indicates the dimension is attached.
Figure 7. Dimensions can be reattached to different objects.

AutoCAD then steps through each end of each dimension in turn. Any unassociated dimension points are identified with a blue X (figure 5). Using a running object snap or a snap override, pick the point on the target object to which you want to attach the dimension. Note that it does not have to be the original attachment point-you can deliberately move the attachment point to another object.

When their turn comes up, any associated points are indicated as a blue X within a square box (figure 6). You can press to keep the association or simply snap to another location on another object.

When you are finished, everything updates (figure 7).

Captain, the dimensions seem to be reproducing!

If you copy an object or objects, and if you include any associated dimensions in the same selection set to be copied, the new dimensions are automatically associated to the new objects.

True associative dimensions work as well on objects in Layout mode as they do in model space.

But wait! There's more!

Away team returning, Captain. We are now ready to study the new trans-spatial dimensions in Layout mode.

Trans-spatial dimensions? Someone's been watching too many Star Trek reruns.

No, that's what they're called.

Start a new drawing, using the ANSI A template. When the title block appears, click on the Model tab to switch to model space. Draw a circle with a radius of 10 units.

Now click on the ANSI A Title Block tab to switch to Layout mode. Your circle is so large that it probably won't show in the viewport.

Figure 8. Draw a circle in model space, then zoom and pan to fit the paper space viewport.

Click on the Paper button at the right end of the status bar. This shifts you to model space, as seen through the paper space viewport. Zoom to a value of 0.2XP, and pan as needed to fit the circle nicely in the viewport, as shown in figure 8. I changed the Viewport layer to red to make it more visible.

Click on the Model button at the right end of the status bar to shift back to paper space.

Apply a standard Diameter dimension to the circle and observe how it picked up the true size of the circle in model space (figure 9).

Figure 9. The dimension spans through from paper space to model space.

Congratulations! You have just created a 1:5 scale drawing without adjusting the dimension scale or text size!

Now here comes the cunning part. Click on the Paper button again to return to model space. Note how an image of the dimension followed you from paper space to model space.

Click on Modify | Properties, then click on the circle. Change its diameter to 15 units. The dimension reflects the new size. Click on the Model button to return to paper space, and, like magic, the dimension updates (figure 10).

Figure 10. The paper space dimension reflects model space edits.

Fascinating, Captain. It would seem that the combination of true associative dimensions and trans- spatial dimensions should virtually eliminate all problems associated with setting or changing the scale of a drawing, and with editing a drawing.

It would seem so. In fact, if you change the zoom ratio of the viewport, or move any model space objects, the dimensions still attach and update properly. When you pan the viewport view, it seems that they lose their associativity. No problem-in paper space, click Dimension | Update and select the affected dimensions. They reattach themselves properly.

They work equally well with 2D and 3D geometry at any scale, so they will be of use to virtually every AutoCAD user in every discipline.

You can easily create several views at different scales, and change the scale of views, all with one dimension style that is "full size". You do all plotting from the layout, and therefore you can plot 1:1 regardless of the viewport scales. It is no longer necessary nor desirable to put dimensions in model space at all.

The standard template files include a polygon viewport boundary. Better practice is to use rectangular boundaries, because then you can modify the properties of the viewport to lock the zoom ratio and pan position.

This is all very good, Captain, but we often need to collaborate with crews working in other quadrants.

Not a problem. The new dimensions will survive a round trip out to Release 13 and back. Obviously, they are not associative and trans-spatial in the earlier releases, but they are when they come back to 2002.

Captain, sensors have detected a Buddhist monk. He is in a dentist's chair, but has refused novocaine.

Yes?

He wants to transcend dental medication.

Ouch.

And Now For Something Completely Different
When you wash out wine bottles so you can refill them with your homemade plonk, there is a trick. Invert the bottle and give it a quick swirling shake to set up a whirlpool effect. Incoming air is able to enter more easily up the hollow cone of the whirlpool, so the bottle drains about 30% faster.


AutoCAD Tips!

Lynn Allen

Autodesk Technical Evangelist Lynn Allen guides you through a different AutoCAD feature in every edition of her popular "Circles and Lines" tutorial series. For even more AutoCAD how-to, check out Lynn's quick tips in the Cadalyst Video Gallery. Subscribe to Cadalyst's free Tips & Tools Weekly e-newsletter and we'll notify you every time a new video tip is published. All exclusively from Cadalyst!
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