Apply or Remove Geometric Constraints

Geometric constraints associate geometric objects together, or specify a fixed location or angle.

NoteThis topic has been included for AutoCAD-compatibility purposes only. In AutoCAD LT, parametric drawing technology is limited to displaying and hiding constraints, editing constrained geometry, and changing values in the Parameters Manager.

For example, you can specify that a line should always be perpendicular to another one, that an arc and a circle should always remain concentric, or that a line should always be tangent to an arc.

When you apply a constraint, two things occur:

  • The object that you select adjusts automatically to conform to the specified constraint
  • By default, a gray constraint icon displays near the constrained object as shown in the previous illustration, and a small blue glyph displays with your cursor when you move it over a constrained object

Once applied, constraints permit only those changes to the geometry that do not violate the constraints. This provides a method for exploring design options or making design changes while maintaining the requirements and specifications of the design.

NoteThe order in which you select two objects when you apply a constraint is important in some cases. Normally, the second object you select adjusts to the first object. For example, when you apply a perpendicular constraint, the second object you select will adjust to become perpendicular to the first.

You can apply geometric constraints to 2D geometric objects only. Objects cannot be constrained between model space and paper space.

Specify Constraint Points

With some constraints, you specify constraint points on objects instead of selecting the objects. This behavior is similar to that of object snaps, but the locations are limited to endpoints, midpoints, center points, and insertion points.

For example, a coincident constraint can restrict the location of the endpoint of one line to the endpoint of another line.

The following glyph is displayed on the object as you roll over the object.

You use this glyph to confirm whether you are specifying the intended point to constrain.

The fix, horizontal, and vertical constraint icons indicate whether the constraints are applied to an object or a point.

Constraint Point Object
Fix

Horizontal

Vertical

The symmetric constraint icons indicate whether it identifying a symmetrical point or object, or the symmetrical line.

Constraint Point Object Line
Symmetric

When rolling over any icon, the constraint point markers are displayed indicating the constrained points. You do not need to roll over the icon to identify the constraints that are applied to the points of the selected object.

A different set of constraint bar icons are displayed when a horizontal or vertical constraint is not parallel or perpendicular with the current UCS.

Use Fix Constraints

A fix constraint associates a constraint point on an object, or the object itself with a fixed location with respect to the World Coordinate System.

It is often advisable to specify a fix constraint at an important geometric feature. This locks the location of that point or object, and prevents geometry from relocating when you make changes to the design.

When you fix an object, the angle of a line, or the center of an arc or circle is also fixed.

Apply Multiple Geometric Constraints

You can apply multiple geometric constraints to objects either manually or automatically.

When you want to apply all essential geometric constraints to a design automatically, you can use AUTOCONSTRAIN with the objects that you select in your drawing. This helps constrain the geometric shape of the design—depending on your design, there might be cases where you need to apply additional geometric constraints.

AUTOCONSTRAIN also provides settings in which you can specify the following options:

  • What geometric constraints to apply
  • What order to apply geometric constraints
  • What tolerances are used to determine whether objects are horizontal, vertical, or touching
NoteFix constraint is not applied with AUTOCONSTRAIN. You must apply the constraint individually. Equal constraint applied with AUTOCONSTRAIN resizes the selected arcs to the same radius only. It is not applied to the arc length.

To fully constrain the size and proportions of a design, you will later need to apply dimensional constraints.

Remove Geometric Constraints

A geometric constraint cannot be modified, but you can delete it and apply a different one. Several constraint options, including Delete, are available from the shortcut menu that is displayed when you right-click a constraint icon in the drawing.

You can delete all constraints from a selection set in a single operation with DELCONSTRAINT.

Commands
CONSTRAINTBAR

Displays or hides the geometric constraints on an object.

CONSTRAINTSETTINGS

Controls the display of geometric constraints on constraint bars.

System Variables
CONSTRAINTBARMODE

Controls the display of geometrical constraints on constraint bars.

CONSTRAINTNAMEFORMAT

Controls the text format for dimensional constraints.

CONSTRAINTRELAX

Indicates whether constraints are enforced or relaxed when editing an object.

CONSTRAINTSOLVEMODE

Controls constraint behavior when applying or editing constraints.