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Home: AutoCAD 2010 User Documentation
Overview of Geometric Constraints
Constrain Objects Geometrically
Display and Verify Geometric Constraints
Apply or Remove Geometric
Constraints
Geometric constraints
associate geometric objects together, or specify a fixed location
or angle.
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, the 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.
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
NoteEqual or Fix constraints
are not applied with AUTOCONSTRAIN. You must apply these constraints
individually.
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.
To apply a coincident constraint
- Select the first and second points on
two different objects.
The second point is made
coincident to the first.
To apply a collinear constraint
- Select the first and second object. You
can select either a line object or a polyline subobject.
The second object is
made collinear to the first.
To apply a concentric constraint
- Select the first and second arc or circle
object.
The second arc or circle
moves to have the same center point as the first object.
To apply a fix constraint
- Select a point on an object.
Applying the Fix constraint
to a point on the object locks the node in place. You can still
move the object.
To apply a parallel constraint
- Select the two objects to be made parallel.
You can select either a line object or a polyline subobject.
The second object is
made parallel with the first object.
To apply a perpendicular constraint
- Select the two objects to be made perpendicular.
You can select either a line object or a polyline subobject.
The second object is
made perpendicular to the first object.
To apply a horizontal constraint
- Select the line object or polyline subobject
to be made horizontal.
To apply a vertical constraint
- Select the line object or polyline subobject
to be made vertical.
To apply a tangent constraint
- Select the two objects to be made tangential.
The second object maintains
a point of tangency with the first object.
To apply a smooth constraint
- Select the first spline curve.
- Select the second spline, line, polyline
(subobject), or arc object.
The two objects are updated
to be contiguous with one another.
To apply a symmetric constraint
- Select the first and second object.
- Select the symmetry line.
The selected objects
become symmetrically constrained about the selected line.
To apply an equal constraint
- Select the first and second object.
The second object is
made equal to the first object.
To apply multiple geometric constraints
to an object
- Select the objects that you want to constrain.
- Press Enter when you select the objects
to be automatically constrained.
The Command prompt displays
the number of constraints applied.
To set the order for applying multiple
geometric constraints to an object
- At the Command prompt, enter s (Settings).
- In the Constraint Settings dialog box,
on the AutoConstrain tab, select a Constraint Type.
- Click Move Up or Move Down. This changes
the priority for a constraint when you use the
AUTOCONSTRAIN command on an
object.
- Click OK.
Commands
GEOMCONSTRAINT
A toolbar-like UI element
that displays the available geometric constraints on an object.
CONSTRAINTBAR
A toolbar-like UI element
that displays the available 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.
CONSTRAINTBARDISPLAY
Displays constraint
bars for objects after you manually apply a constraint or autoconstrain
them.
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.
