Hello all,
I am creating a parameterized drawing and I ran into a problem. I am able to create functions using other dimensions and user parameters. But when i try to use reference parameters I get an error. I am not using this number to drive anything, just calculate some ratio. Is there no way to use a reference parameter in an equation?
Thanks, Sami
Hello @Anonymous,
A reference parameter is a driven dimensional constraint, either dynamic or annotational it only reports a measurement similar to a dimension object. You can use dimensional constraint parameter set to an expression that includes a function, in parentheses to determine the precedence of operations.
When a dynamic dimensional constraint references one or more parameters, the prefix fx:is added to the name of the constraint. This prefix is displayed only in the drawing. Its purpose is to help you to avoid accidentally overwriting parameters and formulas when the dimension name format is set to Value or Name, which suppresses the display of the parameters and formulas.
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Natasha
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Since a reference dimension is in essence a constant perhaps you can create a constant as a workaround and reference it in the constraint dimension with the function.
For example, the following Parameters Manager panel includes a contant named "c2" under User Parameters. The constrained dimension for dia1 references it and the value of d1, a constrained dimension. You can change the value of c1 but not of reference dimension d2. This runs the risk of having d2 and c2 with different values but if you think d2's value is going to change then perhaps it shouldn't be a reference dimension!
@JBerns wrote:
... does AutoCAD 2026 now have the ability to use reference dimensions in equations?
Unfortunately, still not. In my opinion, this is one of the major shortcomings of AutoCAD's parametric capabilities. And yes, other programs can and do allow this. Why not AutoCAD? Ask the developers...
Jürgen Palme
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Semantics aside, I would not consider a reference dimension to be a constant.
For example, the block below contains linear dimensional parameters to control overall length and hole offsets.
Given the "internal" hole spacing, the number of holes in the array can be calculated to fill the remaining space.
In other CAD systems I can create a reference dimension between the first and last holes. It would not be a constant since the lengths and offsets could change.
Granted, the "remaining" area would be the equation, OAL - Hole_Start_Offset - Hole_Finish_Offset.
A reference dimension would avoid having to use such a long expression in an equation.
The workaround is to create a User Parameter to store the value. Then use the User Parameter in an equation.
When switching between CAD systems, it can be expected that workflows and practices may change.
When working within the same family (Autodesk products), I was surprised to discover that AutoCAD did not support methods common in Inventor and Fusion.
Reference dimensions would certainly add convenience.
Regards,
Jerry
@JBerns I agree that it should be possible to use a reference dimension in an expression. In fact, when adding a dimension that would overly constrain geometry the user gets the following message stating the it CAN be used in an expression.
However, when tryng to create an expression that uses the reference dimension the user sees the following and, as you know, the expression is not accpeted.
It would appear that this inconsistency should be easy to fix by AutoCAD.
My suggestion was meant as a workaround that may be helpful in certain situations.
as an Example, will need a reference parameters for P1V7, which is coincident with a non centered crossing horizontal line and the circle, to recalculate P1V7 (which can be 0.01 near to 0, or a floored number for an array). I know there're alternative ways in inserting geometry formulas, but if the reference PARAMETERS are usable in expression will save allot of time and effort, and also because they named them as PARAMETERS, why not allowing users to use it as REFERENCE in their expression?
