Driving 2D Dimensions

In order to fully define a drawing based on sketch lines, you should create dimensional constraints in addition to the geometric constraints. Informational dimensions indicate but do not define dimensional parameters of graphic lines, i.e. a corresponding parameter, and therefore a dimension value, might change arbitrary upon editing the drawing. A driving dimension defines the corresponding parameter of its base elements. In result, the specified dimension value is always preserved upon further changes of the drawing, unless the value is edited manually by the user, which leads to corresponding changes in graphic lines' geometry.

A driving dimension may be based on:

•a single sketch line, so the dimension defines its size (length of straight line or curve, radius or diameter of circle or circular arc, length of axis of ellipse or elliptic arc);

•two sketch lines, so the dimension defines distance or angle between them;

•two free 2D nodes, so the dimension defines distance between them;

•a sketch line and a 2D construct (2D node of any type, straight line, circle), so the dimension defines distance or angle between them.

Driving dimensions do not affect the geometry of construction lines and non-free 2D nodes. If a specified value of a driving dimension requires changing geometry, then geometry gets changed for sketch lines and free 2D nodes only.

Manual creation of driving dimensions

To create a driving dimension manually, you need to use the standard Dimension command, with the Driving Dimension creation mode enabled:

All dimensions created, while this mode is active, are the driving ones, except cases, where creation of a driving dimension would lead to over-defining the drawing, i.e. where parameters of lines to be defined by such dimension are already defined by other driving dimensions or constraints. In such cases, a non-driving dimension gets created, regardless of the active driving dimension creation mode; however, the mode stays active.

Upon placing a driving dimension in the drawing, you will be prompted to enter a dimension value, because the Edit driving dimension value on creation option is enabled by default in the parameters window of the Dimension command. You can enter a number, a variable name or an expression, as a value of a driving dimension.

Turning a non-driving dimension into a driving one manually

Any existing non-driving dimension based on suitable elements can be converted into a driving one and vice versa. To do so, enable or disable the Driving checkbox in the contextual menu of dimension.

Automatic conversion of a dimension into driving one, upon editing its value

The Set "Driving" parameter when editing checkbox is enabled by default in system options ( Options > Constraints and dimensions > Create Dimensions Automatically). In result, any 2D dimension automatically becomes a driving one, when the user manually changes its value this way.

Automatic creation of driving dimensions

When drawing a sketch, you can use the automatic creation of dimensions mode. Using it simultaneously with the driving dimensions creation mode result in automatic creation of driving dimensions.

The Find and Infer Constraints command allows to create driving dimensions and constraints automatically for already created sketch lines.

Driving dimensions display

By default driving dimensions are printable, like any other dimension. If you don't want a dimension to be printable, make it auxiliary.

The fact, that dimension has become driving, is easy to notice by its background, since, unlike informational dimensions, the values of the driving dimensions are highlighted by the colored background. The background color shows the different states of drawing geometry as a whole (see the Graphic Lines' Degrees of Freedom section).

Suppression of driving dimensions

Driving dimensions can be suppressed. A suppressed driving dimension works like a generic informational dimension, i.e. it doesn't affect the geometry of drawing, and dimension value changes in accordance with geometry changes, when editing the geometry. Upon disabling the suppression, the dimension becomes driving again, and its value gets restored to the one existed at the moment of enabling the suppression.

See Also:

•Dimension

•Constraints

•Driving 3D Dimensions