434 Part IV: Advancing with AutoCAD

To get the best results, you should go at least part way back to drawing with precision. For example, a coincident constraint is applied pretty much any time you use an object snap, while horizontal and vertical constraints are placed if polar or ortho modes are on.

Inferred constraints also work when editing existing geometry.

Inferred Constraints mode is a powerful component of parametric drafting in AutoCAD, but we recommend that first you make yourself familiar with manually applying constraints in the ways we show in this chapter.

AutoConstrain yourself!

The geometric constraints listed in Table 19-1 are meant to be applied one at a time. That flexibility is great, but it can be pretty darned time consuming to go around a complex object, trying to figure out what the best constraint option would be and then applying it.

The Auto Constrain button on the Parametric tab’s Geometric panel can apply a whack of constraints to a selection of objects with a single click — but before you execute that single click, it’s worth taking a look at the Auto Constrain settings. Click the dialog box launcher (the little arrow at the right end of the Geometric panel label) to open the Constraint Settings dialog box and make the AutoConstrain tab active (see Figure 19-7). Choose which constraints you want to apply automatically, and in what order you want them in the list, so that the ones that should take precedence have a higher priority. Your best bet initially is to stick with the defaults until you become more familiar with things.

Auto Constrain works only with geometric constraints, not with dimensional constraints.

AutoCAD won’t let you overconstrain an object. For example, if you have a horizontal constraint on one line and a parallel constraint between it and a second line, AutoCAD will object if you try to add a horizontal constraint to the second line.

The three buttons at the right side of AutoCAD’s Geometric panel — and the only buttons on AutoCAD LT’s Geometric panel — are for controlling the visibility of geometric constraint markers. Show All shows them all, and Hide All (surprise!) hides them all. Use the Show/Hide button to display the constraints on selected objects. This last button is a little clunky. It would be nice to be able to hover the mouse pointer over an object and have the constraints show, but you actually have to click an object and then press Enter to see any results.

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