2D constraints

Parametric constraints are used to maintain relationships and control dimensions of 2D geometry.

There are two types of constraints:

  • Geometrical constraints control relationships between entities.
  • Dimensional constraints are used to control the dimensions of an entity, such as length, angle, radius or diameter.

A dimensional constraint can use a value or a formula, with other dimension constraints or parameters. Dimensional constraints can be edited in the Parameters and Constraints panel and in the Mechanical Browser panel.

Note:
  • It is recommended to first apply geometric constraints, then dimensional constraints.
  • The PARAMETERCOPYMODE system variable controls how constraints and related parameters are processed when constrained entities are copied.
  • The PARAMETRIZE2D command automatically creates geometrical and dimensional parameters.
When using constraints a drawing can be in one of three states:
  • Underconstrained: some entities are constrained. It might be impossible to apply some changes using modification commands and procedures.
  • Fully constrained: all possible and relevant geometric and dimensional constraints are applied to the design geometry. The drawing can be modified only by changing the values of the dimensional constraints.
  • Overconstrained: one or more constraints violate or contradicts other constraints.
Parametric constraints allow to:
  • Maintain geometric design intent.
  • Make multiple versions of a design by applying different values to dimensional constrains.
Figure 1. Two versions of the same fully constrained drawing representing a roundabout

Commands and toolbars

2D parametric constraints tools are located on the 2D Constraints toolbar and the Parametric ribbon tab.

Tools to control the display of constraint bars and geometrical constraints are located on two flyout toolbars: Dimensional Constraint and Geometric Constraint.

Command Description
DCDISPLAY command Allows to set dimensional constraints to be displayed or hidden.
GEOMCONSTRAINT command Applies geometric relationships between entities and/or valid constraint points on entities.
GCFIX command Constrains points and entities at a fixed position.
GCCOINCIDENT command

Applies a coincident geometrical constraint to two points or constraints a point to an entity.
GCCONCENTRIC command Constrains the center points of circles, arcs, ellipses or elliptical arcs to coincide.
GCCOLINEAR command Forces lines or polyline segments to be collinear.
GCPARALLEL command Forces two lines or linear polyline segments to be parallel to each other.
GCPERPENDICULAR command Constrains two lines or polyline segments to lie perpendicularly to each other.
GCTANGENT command

Constrains two entities to maintain a point of tangency to each other or their extensions.

The following entities are accepted: lines, polyline segments, circles, arcs, ellipses or elliptical arcs.
GCHORIZONTAL command Constrains lines, linear polyline segments or pairs of points to lie parallel to the X-axis of the current coordinate system.
GCVERTICAL command Constrains lines, linear polyline segments or pairs of points to lie parallel to the Y-axis of the current coordinate system.
GCSMOOTH command Forces a spline to maintain fluid geometric continuity with another spline, line, arc or polyline.
GCSYMMETRIC command Constrains two entities or points to lie symmetrically with respect to a selected line.
GCEQUAL command Constrains arcs and circles to the same radius, or lines and polyline segments to the same length.
CONSTRAINTBAR command

Controls the display of the constraint bar of entities.

Constraint bars are always hidden when opening a drawing.
DIMCONSTRAINT command

Applies a dimensional constraint to an entity or between constraint points on entities.

Converts associative dimensions to dynamic dimensions.
DCHORIZONTAL command Constrains the horizontal distance (X-distance) between two points with respect to the current coordinate system.
DCVERTICAL command Constrains the vertical distance (Y-distance) between two points with respect to the current coordinate system.
DCLINEAR command Constrains the horizontal distance (X-distance) or vertical distance (Y-distance) between two points with respect to the current coordinate system.
DCALIGNED command Constrains the distance between two points or the length of a line or polyline segment.
DCRADIUS command Constrains the radius of a circle, an arc or an arc polyline segment.
DCDIAMETER command Constrains the diameter of a circle, an arc or an arc polyline segment.
DCANGULAR command Constrains the angle between two lines or linear polyline segments; the total angle of an arc or an arc polyline segment; or the angle between three points on entities.
DCCONVERT command Converts an associative dimension to a dimensional constraint.
DELCONSTRAINT command Removes all dimensional and geometrical constraints from an entity.