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Controlling and informational dimensions. Dimensions with Variables |
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Associative dimensions can be of two types: controlling and informational. The dimension type determines if the dimension affects the geometric object or, vice versa, if the object affects the dimension.
Controlling dimension — the dimension that controls a geometric object.
You can change the controlling dimension value by entering a number, constant or expression (in the last two cases, a variable must be created for the dimension). After this, the geometric object to which the dimension was set is rebuilt to match the new dimension value.
To be controlling, a dimension must be fixed, i.e. have a fixed dimension constraint. A sign of fixation is a rectangular marquee around its value (this marquee is displayed if the display constraints enabled).
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Dimensions can be automatically fixed when they are created in parametric mode. To do this, when setting up the parametric mode the options Associate when entering dimensions and Fix dimensions must be enabled. You can also fix dimensions using the Fix Dimension command. |
The object with a fixed dimension can only be edited in such a way that the value of this dimension remains constant. For example, if a segment has a dimension fixing its length, then this segment can only be moved and rotated but its length cannot be changed.
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When editing geometric objects, not only the dimensions affixed to them but also the parametric constraints applied to them are taken into account. |
Any controlling dimension can be made informational in two ways:
•delete its constraint Fixed Dimension, using the commands Object Constraintsor Delete All Constraints,
•click the Information Dimension 
button in Set dimension value dialog.
Info Dimension is a dimension that is controlled by a geometric object.
You cannot enter a value or an expression for an informational dimension. A geometric object for which an informational dimension is set can be edited in an arbitrary manner. After rebuilding the geometric object, the dimension is rebuilt and its value is recalculated. Constraint Fixed dimension does not exist for informational dimensions.
An informational dimension can be made controlling in two ways:
•using the Fix Dimension command,
•Press the Informational dimension button in the dimension value setup dialog.
However, not every informational dimension can be made controlling, i.e., be fixed. The inability to fix a dimension can be caused by:
•geometric links between objects, for example: the distance between diagonally opposite vertices of a rectangle depends on the lengths of its sides, therefore, if the lengths of the rectangle sides are already fixed then its diagonal length cannot be fixed;
•parametric constraints, for example:
•The angle between two segments, on which the Perpendicularity constraint is imposed, always equals 90°, therefore it is not possible to fix the angle between these segments,
•diameter of a circle mating parallel segments always equals to the distance between them, so, if this distance has already been fixed, the diameter cannot be fixed.
An excessive dimension cannot be fixed either.
When trying to fix a dimension which can only be informational, a relevant message appears.
A variable can be created for both informational and controlling dimensions. To do this, enter its name in the dialog box for setting the dimension value. In the future, you can change the value of the controlling dimension using this variable.
When working with the model, you can change the value of the controlling dimension of the sketch during the execution of an operation, which parent object is the sketch, as well as in the element dimensions display mode of the element built based on the sketch (see the sections Dimensions of sketches and operations: Overview and Changing the operation dimension value).
See Also
Notes on working with associative dimensions and designations
