Use Formulas in Autodesk Revit

To fully utilize the power of parametric content in Autodesk Revit families, it´s important to understand how Revit works with formulas. Though it´s very similar to MS Excel, there are some limitations and software specific issues that you should be aware of.

Steps

  1. Learn how to write a formula for exponentiation: use X raised to the power of Y = X ^ Y
  2. Learn how to write a formula for E raised to an x power
    • E is a mathematical constant that is approximately equal to 2.7. It is an irrational number, but if we truncate it to 20 decimals it would be 2.7182818284590452353.
    • Revit usage = exp(x)
  3. Learn how to find the circumference and area of a circle with a formula in the program:
    • Usage in Revit = pi()
    • Circumference = pi() * (Radius * 2)
    • Circumference = pi() * Diameter
    • Circle Area = pi() * Radius ^ 2
  4. Learn how to find Square Roots of any number in this program.
    • Fixed value = sqrt(999)
    • Parameter = sqrt(Width)
    • Formula= sqrt(Width + Height)
  5. Learn how to solve logarithm problems.
    • The logarithm of a number to a given base is the exponent to which the base must be raised in order to produce that number. For example, the logarithm of 1000 to base 10 is 3, because three factors of 10 must be multiplied to yield a thousand: 10 × 10 × 10 equals 1000
    • Revit usage = log(1000)
  6. Learn how to force yes/no parameters to be checked or unchecked.
    • Force checked = 1 < 2
    • Force unchecked = 1 > 2
  7. Learn how to solve conditional statements. Conditional statement uses this structure:
      • IF (<condition>, <result-if-true>, <result-if-false>)
    • Supported Conditional Operators
      • < Less than
      • > Greater than
      • = Equal
      • / Divide
      • AND Both statements are true
      • OR One of the statements is true
      • NOT Statement is false
    • Conditional statements can contain numeric values, numeric parameter names, and Yes/No parameters. 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)
    • Simple IF Statement
      • IF (Length < 900, <true>, <false>)
    • Formula That Returns Strings
      • IF (Length < 900, “Opening too narrow”, “Opening OK”)
    • Using logical AND
      • IF ( AND (x = 1 , y = 2), <true>, <false>)
      • Returns <true> if both x=1 and y=2, else <false>
    • Using logical OR
      • IF ( OR ( x = 1 , y = 2 ) , <true>, <false>)
      • Returns <true> if either x=1 or y=2, else <false>
    • Nested IF statements
      • IF ( Length < 500 , 100 , IF ( Length < 750 , 200 , IF ( Length < 1000 , 300 , 400 ) ) )
      • Returns 100 if Length<500, 200 if Length<750, 300 if Length<1000 and 400 if Length>1000
    • IF with Yes/No condition
    • Length > 40
    • Returns checked box (<true>) if Length > 40
    • NOT with Yes/No condition
      • not(Viz)
      • Returns checked box (<true>) if Yes/No parameter "Viz" is unchecked, and returns unchecked box (<false>) if Yes/No parameter "Viz" is checked.
    • IF AND OR Returning the greatest of three values
      • Say you have these 3 length parameters, and want a fourth parameter to return the greatest value/length of the 3:
      • Length A
      • Length B
      • Length C
      • Return Length (Returns the greatest of the three length parameters)
      • Return Length = if(and(or(Length A > Length B, Length A = Length B), or(Length A > Length C, Length A = Length C)), Length A, if(and(or(Length B > Length A, Length B = Length A), or(Length B > Length C, Length B = Length C)), Length B, if(and(or(Length C > Length A, Length C = Length A), or(Length C > Length B, Length C = Length B)), Length C, 0 mm)))
      • Another option is to use an extra "Calc" parameter, which is a bit more clumsy but also way easier and more manageable for us mortals.
      • Calc = if(Length A > Length B, Length A, Length B)
      • Return Length = if(Calc > Length C, Calc, Length C)
  8. Learn how to solve a trigonometry problem in the software.
    • Known: a+b
      • c = sqrt(a ^ 2 + b ^ 2)
      • A = atan(a / b)
      • B = atan(b / a)
    • Known: a+c
      • b = sqrt(c ^ 2 - a ^ 2)
      • A = asin(a / c)
      • B = acos(a / c)
    • Known: b+c
      • a = sqrt(c ^ 2 - b ^ 2)
      • A = acos(b / c)
      • B = asin(b / c)
    • Known: c + A
      • a = c * sin(A)
      • b = c * cos(A)
      • B = 90° - A
    • Known: c + B
      • a = c * cos(B)
      • b = c * sin(B)
      • A = 90° - B
    • Known: a + B
      • b = a * tan(B)
      • c = a / cos(B)
      • A = 90° - B
    • Known: b + A
      • a = b * tan(A)
      • c = b / cos(A)
      • B = 90° - A
    • Known: a + A
      • b = a / tan(A)
      • c = a / sin(A)
      • B = 90° - A
    • Known: b + B
      • a = b / tan(B)
      • c = b / sin(B)
      • A = 90° - B

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