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Joined: Fri, Aug 25, 2006
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i am a 2nd year architecture student and we have been given a project to do on revit. we have a problem and that is with setting up a parameter, it is so confusing!can someone please help me? one of the restraints are as follows:
A variety of structural elements whose proportions are constant ( in other words , the higher the structure the wider the structure), but any structure below 3 metres should be concrete and should follow the inverse of this rule (within reason).
please can someone help me understand how one sets up a parameter?
thanks so much.
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Hi there , I'm not quite understanding your question. Are you trying to control the width of your structural element as it goes higher with a parameter?
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the higher the structure the wider it goes, and the inverse of this rule applies so as you go lower down it goes thinner. so basically i am trying to keep the proportions of the structural element constant i just have no clue how to so it.
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Is there any possibility of you posting an image of what you want to do? I think I understand what oyu want to do but I'm not certian.
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i havent even thought of the design as yet, the whole point of this exercise is to understand how to set parameters and families and how that in turn would drive your design.i will try and post an image as soon as i can thanks for all your help i truely appreciate it.
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I made a simple parametric cube to illustrate the use of formulas in parameters. In this case there is an IF statement which evaluates the Height of the cube, tests against a condition and does the math to drive the Width of the cube relative to its height.
Formulas in families are an advanced Revit topic and without guidance from a well written book such as the Revit AOTC course, or attending Autodesk University's Revit families classes it will be dificult for most users.
HTH
Tom
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thanks so much for your help, i am unable to open the file as we are using revit version 8.1.
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Try this version created in 8.1 and see if it is what you are looking for.
Tom
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Thanks tomdinmn been a little busy of late! 
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thanks so much for your help i really appreciate it, and will let you know once ive worked through it.
thanks again, have a good day
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You can get pretty creative with condition formulas in Revit. I just used the most basic of formulas. For further help see the Revit help file or the section below from it on conditional formulas.
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You can use conditional statements in formulas to define actions in a family that depend on the state of other parameters. With conditional statements, the software enters values for a parameter based on whether a specified condition is satisfied. Conditional statements are useful in certain circumstances; however, they make families more complex and should be used only when necessary.
For most type parameters, conditional statements are unnecessary, because the type parameter itself is like a conditional statement: If this is the type, then set this parameter to a specified value. Instance parameters are a more productive place to use conditional statements, particularly when they are used to set a parameter that does not vary continuously.
Syntax for Conditional Statements
A conditional statement uses this structure: IF (<condition>, <result-if-true>, <result-if-false>
This means that the values entered for the parameter depend on whether the condition is satisfied (true) or not satisfied (false). If the condition is true, the software returns the true value. If the condition is false, it returns the false value.
Conditional statements can contain numeric values, numeric parameter names, and Yes/No parameters. You can use the following comparisons in a condition: <, >, =. You can also use Boolean operators with a conditional statement: AND, OR, NOT. Currently, <= and >= are not implemented. To express such a comparison, you can use a logical NOT. For example, a<=b can be entered as NOT(a>b).
The following are sample formulas that use conditional statements.
Simple IF: =IF (Length < 3000mm, 200mm, 300mm)
IF with a text parameter: =IF (Length > 35', “String1”, “String2”)
IF with logical AND: =IF ( AND (x = 1 , y = 2), 8 , 3 )
IF with logical OR: =IF ( OR ( A = 1 , B = 3 ) , 8 , 3 )
Embedded IF statements: =IF ( Length < 35' , 2' 6" , IF ( Length < 45' , 3' , IF ( Length < 55' , 5' , 8' ) ) )
IF with Yes/No condition: =Length > 40 (Note that both the condition and the results are implied.)
Examples of Conditional Statement Usage
Typical uses for conditional statements in formulas include calculating array values and controlling an element’s visibility based on a parameter value. For example, you can use conditional statements to:
Prevent an array parameter from taking a value less than 2.
In Revit Building, arrays can only have an integer value of 2 or greater. In some situations, it may be useful to create a conditional formula that maintains an array parameter of 2 even if the calculated value is 1 or 0. With such a formula, if the calculated array value is 2 or greater, the formula retains the value. However, if the calculated value is 1 or 0, the formula changes the value to 2.
Formula: Array number = IF (Arrayparam < 2, 2, Arrayparam)
Make muntins visible only when the number of window lights is greater than 1.
For example, if you have a Lights parameter that you want to use to control the visibility of muntin geometry, you can create a Yes/No parameter like MuntinVis, and assign it to the Visible parameter in the Element Properties dialog of the muntin geometry. Because the MuntinVis parameter is a Yes/No (or Boolean) operation, both the condition (IF) and the results are implied. In this example, when the condition is met (true), the MuntinVis parameter value is selected, and the muntin geometry is visible. Conversely, when the condition is not met (false), the MuntinVis parameter is cleared, and the muntin geometry is not visible.
Formula: MuntinVis = Lights > 1
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