Tutorial: 2D Dimensional Constraints
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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.
In the example below:
- The width and opening angle are controlled by dimensional constraints.
- Coincident geometrical constraints () are applied to the endpoints of the arc and the polyline and to the center point of the arc and the polyline vertex.
- The polyline segments have an equal () geometrical constraint.
- One segment of the polyline has a horizontal () geometrical constraint.
- The polyline vertex has a fix () geometrical constraint.
Parametric constraints allow to:
- Maintain geometric design intent.
- Make multiple versions of a design by applying different values to dimensional constrains.
Two versions of the same fully constrained drawing representing a roundabout |
NOTE |
It is recommended to first apply geometric constraints, then dimensional constraints. |
When using constraints a drawing can be in one of three states:
- Unconstrained: no entities are constrained. The drawing can be modified using modification commands and procedures.
- 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.
Commands and toolbars
2D parametric constraints tools sit on the 2D Constraints toolbar:
Tools to control the display of constraintbars and geometrical constraints sit on two flyout toolbars:
Dimensional Constraint :
and Geometric Constraint:
Command |
Icon |
Description |
Geometric Constraints |
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Allows to set dimensional constraints to be displayed or hidden. |
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Shows all dimensional constraints. |
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Hides all dimensional constraints. |
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Applies geometric relationships between entities and/or valid constraint points on entities. |
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Constrains points and entities at a fixed position. |
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Applies a coincident geometrical constraint to two points or constraints a point to an entity. |
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Constrains the center points of circles, arcs, ellipses or elliptical arcs to coincide. |
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Forces lines or polyline segments to be collinear. |
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Forces two lines or linear polyline segments to be parallel to each other. |
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Constrains two lines or polyline segments to lie perpendicularly to each other. |
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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. |
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Constrains lines, linear polyline segments or pairs of points to lie parallel to the X-axis of the current coordinate system. |
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Constrains lines, linear polyline segments or pairs of points to lie parallel to the Y-axis of the current coordinate system. |
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Forces a spline to maintain fluid geometric continuity with another spline, line, arc or polyline. |
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Constrains two entities or points to lie symmetrically with respect to a selected line. |
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Constrains arcs and circles to the same radius, or lines and polyline segments to the same length. |
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Dimensional Constraints |
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Controls the display of the constraint bar of entities. Constraint bars are always hidden when opening a drawing. |
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Shows all constraintbars. |
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Hides all constraintbars. |
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Applies a dimensional constraint to an entity or between constraint points on entities. Converts associative dimensions to dynamic dimensions. |
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Constrains the horizontal distance (X-distance) between two points with respect to the current coordinate system. |
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Constrains the vertical distance (Y-distance) between two points with respect to the current coordinate system. |
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Constrains the horizontal distance (X-distance) or vertical distance (Y-distance) between two points with respect to the current coordinate system. |
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Constrains the distance between two points or the length of a line or polyline segment. |
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Constrains the radius of a circle, an arc or an arc polyline segment. |
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Constrains the diameter of a circle, an arc or an arc polyline segment. |
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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. |
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Converts an associative dimension to a dimensional constraint. |
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Removes all dimensional and geometrical constraints from an entity. |
NOTE |
The PARAMETERCOPYMODE system variable controls copying of constraints and related parameters when entities are copied. 0: Do not copy 2D constraints. |