Parametric Constraints …the Series. PART 2


The 2D parametric functionality in AutoCAD 2011 has been enhanced, and includes predefined command macros to access options within in the GEOMCONSTRAINT and DIMCONSTRAINT commands automatically for you. For example, instead of launching the GEOMCONSTRAINT command and then selecting the perpendicular option, you can launch the GCPERPENDICULAR command directly all in one step. Repeating the last command automatically repeats the last command as well as the specific option, so this will help in speeding up the process. Object highlighting; when you roll over an icon on a constraint bar or when you select a parameter in the Parameters manager supports the Visual Effects settings you specify on the Selection tab of the Options dialog box (dashed and thickened by default), so it make it easy to see what constraints are assigned to what objects. Additional improvements to geometric and dimensional constraint functionality enable you to create and edit parametrically constrained geometry faster than ever before.

Geometric Constraints
AutoCAD 2011 significantly simplifies the process of adding geometric constraints to 2D AutoCAD geometry. AutoCAD can infer geometric constraints as you create and modify geometry. A new INFER Constraint button located on the status bar enables you to toggle on and off inferred constraints similar to the toggle for object snaps and other drafting settings. This toggle is also available on the Geometric tab of the Constraint Settings dialog box. (Tip: If you don’t like the Icon version on the status bar you can rick-click on the icon and uncheck “Use Icons” to see the “Text” version displayed.)

Infer Constraints tool

Infer Constraints tool

Using inferred constraints automatically applies coincident constraints for Endpoint, Midpoint, Center, Node, and Insertion objects snaps. For example, if you draw a circle by snapping its center to the midpoint of a line, AutoCAD automatically applies a coincident constraint between the center of the circle and the midpoint of the line. If you move the circle, the line goes with it. The same powerful functionality applies to editing commands. If, for example, you copy the insertion of a block to the endpoint of a line, AutoCAD automatically applies a coincident constraint between those two points. When you move the line, the block maintains its position at the endpoint of the line. Tip: Remember if you are not using Inferred option and are just adding constraints manually; to select them in the correct order; just read the prompt as you go.

Editing with inferred constraints

Editing with inferred constraints

In addition to creating point‐to‐point coincident constraints with the previously mentioned object snaps, you can use the Nearest object snap to apply a coincident constraint between a point and an object. For example, if you draw the center of a circle on a line using the Nearest object snap, the center of the circle has the flexibility of moving anywhere along the line including the virtual extension of the line.

Nearest object snap with inferred constraints

Nearest object snap with inferred constraints

The Perpendicular and Tangent object snaps automatically apply perpendicular or tangent constraints between the object being created or edited and the object being snapped to. They also apply a point‐to-point or point‐to‐object coincident constraint if appropriate. Using the Parallel object snap automatically applies a parallel constraint but no coincident constraints are applied since, by definition, the two objects never intersect. When you draw horizontal or vertical lines and polyline segments, inferred horizontal and vertical constraints automatically apply to those segments. Inferred constraints enhance the behavior of rectangles, fillets, and chamfers by automatically applying appropriate geometric constraints. For example, if you draw a rectangle (using the RECTANG command), AutoCAD will automatically apply a pair of parallel constraints and a perpendicular constraint to the rectangle. So, when you modify the size and shape of the rectangle,(like grip editing from the corner) it will remain as a rectangle shape with parallel sides and perpendicular at the corners.  Next Blog we will look at how it will constrain fillets and other objects with the Infer Constraints in PART 3… so check back in about 2 weeks to see the continuation of Parametric Constraints.

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