Parameters and rules

Parameters

Each feature value in Meridian is a named parameter. For example, the distance of the first extrude is Extrude1_Distance. You can also add user parameters.

To see and change the parameters, select Tools > Parameters.

Expressions

A parameter value can be a number or an expression.

Example	Result
`25`	25 in the document unit. In a millimeter document, this is 25 mm. In an inch document, this is 25 in.
`2 in`	2 inches (50.8 mm).
`120/2`	Meridian keeps the value 60 mm.
`Thickness * 2`	Two times the parameter `Thickness`.
`Sqrt(Width ^ 2 + Height ^ 2)`	The diagonal of a rectangle.

Units

You can write these units after a number: mm, cm, m, in and deg. A number without a unit uses the unit of the document. Angles are in degrees.

Operators

Operator	Meaning
`+` `-` `*` `/`	Add, subtract, multiply, divide
`\`	Integer division (Meridian rounds both values, divides, and removes the fraction)
`^`	Power
`Mod`	Remainder

Functions

Group	Functions
Trigonometry	`Sin`, `Cos`, `Tan`, `Asin`, `Acos`, `Atan`
Trigonometry in degrees	`SinD`, `CosD`, `TanD`, `AsinD`, `AcosD`, `AtanD`
Angle conversion	`Radians`, `Degrees`
Rounding	`Round`, `Ceiling`, `Floor`, `Int`, `Fix`
Other	`Sqrt`, `Abs`, `Min`, `Max`, `Exp`, `Log`, `Sign`
Constant	`PI`

In a parameter expression, Meridian knows when a value is an angle. Thus Sin, Cos and Tan of an angle parameter use its degrees. In a rule, these functions use radians. Refer to Angles in rules.

References

Use a parameter by its name, for example Width. You can also write Param("Width") or Parameters("Width").
Use a document property with Property("name") or Properties("name").

Rules for expressions

A parameter expression must give a number. Text and True/False values are not permitted.
The result must have the correct kind of unit. If you enter an area for a length, Meridian shows "The expression gives an area. Enter a length."
A count, for example the count of a pattern, must be a whole number from 1 to 2500.

Meridian Rules

A rule is a short program that changes parameters and properties. The language is similar to Visual Basic.

To write and run rules, select Tools > Rules. To run the selected rule, select Tools > Run Rule.

Example

' Comments start with ' or //
Extrude1_Distance = 35
Param("BoltPattern1_Count") = Round(Extrude1_Distance / 5)
Properties("Revision Number") = "R1"
Dim ratio = 0.5

If Extrude1_Distance >= 30 And Properties("Material") <> "Aluminum" Then
    EdgeFillet1_Radius = 4
ElseIf Extrude1_Distance < 10 Then
    EdgeFillet1_Radius = 1
Else
    EdgeFillet1_Radius = 2
End If

Statements

Statement	What it does
`Name = value`	Sets a parameter.
`Param("name") = value`	Sets a parameter. `Parameters("name")` is the same.
`Properties("name") = "text"`	Sets a document property. `Property("name")` is the same.
`Dim name = value`	Makes a variable that only the rule uses.
`If ... Then ... ElseIf ... Else ... End If`	Runs lines only when a condition is true. A short `If` can be on one line.

More operators in rules

Text: & joins two texts. CStr changes a number to text. CDbl changes text to a number.
Comparison: =, <>, <, >, <=, >=.
Logic: Not, And, Or, Xor, AndAlso, OrElse.
True and False.
More functions: Atan2, Atan2D and Log10.

Angles in rules

In a rule, Sin, Cos and Tan use radians. The unit deg does not change a value to radians. Thus Sin(30 deg) is the sine of 30 radians. For degrees, use SinD, CosD and TanD. For example, SinD(30) is 0.5. You can also use Radians(x) and Degrees(x).

How a rule runs

A rule runs as one change. One Undo removes all of the changes of the rule.
If an error occurs, the rule stops. Meridian shows the line of the error and removes all of the changes that the rule made.
Errors include syntax errors, unknown names, wrong types, division by zero, and values that the model does not accept.

Run a rule from the command line

meridian rule part.mpart myrule.txt --save
meridian rule part.mpart -e "Extrude1_Distance = 40" --out part-40.mpart

Refer to Command line.