Time for a change

As Captain LearnCurve and his beautiful wife glided silently homeward from the Rolls-Royce Owners’ Club spring meet, he contemplated the changes going on in the world. With the coming of spring, the local mountains were losing their snowy caps, the flowers were beginning to bloom, the birds were returning, and his granddaughter was learning to walk. By the time you receive this issue, things will have changed again and it will be summer. Luckily, the Rolls-Royce was silent enough that he could hear the anguished cry of a desperate CAD user wafting over the green fields: Oh, woe is me! A whole bunch of things in this drawing are wrong! However shall I change them?

Of all the changes in AutoCAD since I started using it, way back in the last millennium, some of the most significant have occurred in the change functions.

In the good old days, a single command changed drawing objects. It was somewhat limited, but that wasn’t a problem because there wasn’t much that you could change. The color and linetype for each object had to follow its layer, and there was no line weighting or z-axis value.

I have some good news and some bad news. AutoCAD now lets you assign properties to individual objects that are different from the layer properties, and with each succeeding release it becomes easier to change the properties.

Is that the good news or the bad news?

Yes.

Proper properties
I cringed when I first saw the "new, improved" Object Properties toolbar (figure 1) a few releases back. It is normally docked at the top edge of the drawing area. You just click on a toolbar item, and all subsequent objects appear with a different color or a different linetype.

Figure 1. AutoCAD's Object Properties toolbar.

Figure 2. Object Properties pull-down list.

I cringed because I am a firm believer in the philosophy that object properties such as color and linetype should almost always be set by the layer on which they reside, rather than by assigning properties separately. There are two really good reasons for this belief. First, a drawing that is all bylayer is smaller and faster because each object doesn’t need the additional property data.

Second, a bylayer drawing is easier to edit. You can freeze and thaw appropriate layers so that information you don’t need at this time is not visible. The architectural professions in particular make good use of layering schemes.

Can you imagine trying to work on a multimegabyte drawing that is all drawn on one layer, with object properties set individually? I don’t need to imagine it—been there, done that, bought the t-shirt. About the only thing worse is a drawing in which some of the objects have properties set individually and other objects are bylayer.

Now that we’ve seen how easy it is to set the properties for new objects, and why we usually don’t want to, let’s look at how to change them.

Starting with Release 14, changing object properties became ridiculously easy. Once again, that is the good news and the bad news. The good news is that it becomes easier to repair the damage done by other users. Just select objects on screen when no other command is running. The objects highlight and their grip boxes appear.

Now go to the Object Properties toolbar. Click on the down arrow at the right side of the appropriate rectangular window, then click on a property value that appears in the pull-down list as shown in figure 2. All your selected objects take on the desired property.

The windows are not labeled, but here is what they do. From left to right, they:

• Move objects to the selected layer
• Change color
• Change linetype

The AutoCAD 2000 toolbar has two more windows that:

• Change lineweight
• Set plotting characteristics (depending on your plotting setup)

Note that for color, linetype, and lineweight, bylayer is the first choice. Here is where you can correct objects with individual properties attached by making them take on properties of their host layer.

Figure 3. This Ai_propchk dialog box appears when you select several objects.

Other editing options
Let’s start with Releases 13 and 14, because the change functions in AutoCAD 2000 have changed again.

Releases 13 and 14 offer several commands for editing objects, depending on the object in question. These commands appear in the Modify toolbars and pull-down menus.

In addition, one command performs most types of editing functions on most types of objects. This universal command goes by the perfectly obvious name of Ai_propchk. In Release 13, you invoke it by selecting Edit|Properties. Release 14 puts it under Modify|Properties. Release 14 also hides it under the button at the right end of the Object Properties toolbar. And you can always type it in at the Command prompt.

Ai_propchk first invites you to select objects. It then behaves differently depending on what you select.

Figure 4. This or a similar Ai_propchk box displays when you select only one object.

If you select several objects, you see the dialog box shown in figure 3. It lets you specify values for five different properties, which AutoCAD then applies to all objects.

If you select a single object, a more versatile dialog box pops up. Its contents vary according to the type of object you selected. Figure 4 shows the one for a line.

This dialog box lets you edit the same five property values as the multiobject box, but you can also change the values of characteristics that are unique to the selected object. With a line, for example, you can change the location of each end, while a circle can have its center and radius changed. The box also shows information about the object, such as the length and angle of a line or the area and circumference of a circle.

Figure 5. Properties dialog box is new to AutoCAD 2000.

AutoCAD 2000 replaces the Aipropchk command with a new Properties command. You can invoke it in several ways, including pull-down menus and toolbars, but the easiest way is to select one or more objects, then right-click in a blank drawing area. Select Properties from the menu that pops up, and a dialog box similar to that in figure 5 appears.

I say similar because its format depends on the type of object selected. It changes on the fly if you select more objects while it’s open.

You can change the usual properties such as layer and color for all objects, but the Properties command performs many more feats of magic. Unlike in earlier AutoCAD releases, this dialog box lets you change dimensional characteristics for a multiple selection. For example, when I select several circles and type in a new diameter, all selected circles change to the new diameter.

Come back next month to learn many more feats of editing magic that you can perform in AutoCAD 2000.

One final question: How come last month’s column covered the Undo command and this one covered changes?

I can’t plan far enough ahead. Logically, the Undo article should follow this one.

And now for something completely different
You should regularly check the tension in the wire spokes of vehicles that are equipped with such wheels. These include motorcycles, bicycles, vintage and classic cars, and older baby buggies.

When tensioned properly, all spokes give out a clear ringing tone when tapped with a metal object such as a screwdriver. Any that produce a dull thud are loose and must be tightened properly so the vehicle will handle safely at high speeds.