Parametric
drawing is a technology that is used for designing with
constraints. Constraints are associations and
restrictions applied to 2D geometry.
There
are two general types of constraints:
- Geometric constraints control
the relationships of objects with respect to each other
- Dimensional constraints control
the distance, length, angle, and radius values of objects
The following illustration
displays geometric and dimensional constraints using the default
format and visibility.
A blue cursor icon always
displays when you move the cursor over an object that has constraints
applied to it.
In the design phase of
a project, constraints provide a way to enforce requirements when
experimenting with different designs or when making changes. Changes
made to objects can adjust other objects automatically, and restrict changes
to distance and angle values.
With constraints, you
can
- Maintain design specifications and requirements
by constraining the geometry within a drawing
- Apply multiple geometric constraints
to objects instantly
- Include formulas and equations within
dimensional constraints
- Make design changes quickly by changing
the value of a variable
Best PracticeIt is recommended
that you first apply geometric constraints to determine the shape of
a design, and then apply dimensional constraints to determine the size of
objects in a design.
Design Using Constraints
When you are creating
or changing a design, a drawing will be in one of three states:
- Unconstrained. No constraints are applied to any geometry.
- Underconstrained. Some
constraints are applied to the geometry.
- Fully constrained. All
relevant geometric and dimensional constraints are applied to the
geometry. A fully constrained set of objects also needs to include
at least one Fix constraint to lock the location of the geometry.
Thus, there are two general
methods for designing with constraints:
- You can work in an underconstrained drawing
and make changes as you go, using a combination of editing commands,
grips, and adding or changing constraints.
- You can create and fully constrain a
drawing first, and then control the design exclusively by relaxing
and replacing geometric constraints, and changing the values in
dimensional constraints.
The method that you choose
depends on your design practices and the requirements of your discipline.
NoteThe program prevents
you from applying any constraints that result in an overconstrained
condition.
Use Constraints with Blocks
and Xrefs
You
can apply constraints between
- An object in the drawing and an object
within a block reference
- An object within a block reference and
an object within a different block reference (not
between objects within the same block reference)
- The insertion point of an xref and an
object or a block, but not to any objects within xrefs
When you apply constraints
to block references, the objects contained within the block are
automatically available for selection. You do not need to press Ctrl for subobject selection. Adding
constraints to a block reference can cause it to move or rotate
as a result.
NoteApplying
constraints to dynamic blocks suppresses the display of their dynamic
grips. You can still change the values in a dynamic block using
the Properties palette, but to redisplay the dynamic grips, the
constraints must first be removed from the dynamic block.
Constraints can be used
in block definitions, resulting in dynamic blocks. You can control
the size and shape of dynamic blocks directly from within the drawing.
For more information, see Add Constraints to Dynamic Blocks.
Remove or Relax Constraints
There
are two ways to cancel the effects of constraints when you need
to make design changes:
- Delete the constraints individually and
later apply new constraints. While the cursor hovers over a geometric
constraint icon, you can use the Delete key or the shortcut menu
to delete the constraint.
- Relax the constraints temporarily on
selected objects to make the changes. With a grip selected or when
you specify options during an editing command, tap the Ctrl key to alternate between relaxing
constraints and maintaining constraints.
Relaxed constraints are
not maintained during editing. Constraints are restored automatically
if possible when the editing process is complete. Constraints that
are no longer valid are removed.
NoteThe
DELCONSTRAINT command deletes
all geometric and dimensional constraints from an object.
CommandsAUTOCONSTRAIN
Applies geometric constraints
to a selection set of objects based on orientation of the objects
relative to one another.
CONSTRAINTBAR
Displays or hides the
geometric constraints on an object.
CONSTRAINTSETTINGS
Controls the display
of geometric constraints on constraint bars.
DCDISPLAY
Displays or hides the
dynamic constraints associated with a selection set of objects.
DELCONSTRAINT
Removes all geometric
and dimensional constraints from a selection set of objects.
DIMCONSTRAINT
Applies dimensional
constraints to selected objects or points on objects, or converts
associative dimensions to dimensional constraints.
GEOMCONSTRAINT
Displays or hides the
geometric constraints on an object.
LIST
Displays property data
for selected objects.
PARAMETERS
Controls the associative
parameters used in the drawing.
-PARAMETERS
Controls the associative
parameters used in the drawing.
PARAMETERSCLOSE
Closes the Parameters
Manager palette.
TEXTEDIT
Edits a dimensional
constraint, dimension, or text object.
System VariablesCCONSTRAINTFORM
Controls whether annotational
or dynamic constraints are applied to objects.
CONSTRAINTBARDISPLAY
Controls the display
of constraint bars after you apply constraints and when you select
geometrically constrained drawings.
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.
DIMCONSTRAINTICON
Displays the lock icon
next to the text for dimensional constraints.
DYNCONSTRAINTMODE
Displays hidden dimensional
constraints when constrained objects are selected.
PARAMETERCOPYMODE
Controls how constraints
and referenced user parameters are handled when constrained objects
are copied between drawings, Model space and layouts, and block
definitions.
PARAMETERSSTATUS
Indicates whether the
Parameters Manager is displayed or hidden.
