Assigning a global parameter in Revit involves both creating the parameter and then linking it to specific element properties within your model, allowing for centralized control over various dimensions, offsets, or other numeric and textual values. This powerful feature enhances design flexibility and project consistency.
Understanding Global Parameters
Global parameters in Revit are model-wide values that can drive or report dimensions, offsets, or material properties across multiple elements and categories. Unlike project or shared parameters, global parameters exist solely within the project file and cannot be scheduled or tagged directly. Their primary purpose is to establish relationships and consistency across your building information model, making design changes more efficient.
Creating a Global Parameter
The first step to assigning a global parameter is to create it within your Revit project. Follow these steps:
- Access the Global Parameters Dialog: Navigate to the Manage tab in the Revit Ribbon. In the Settings panel, click on Global Parameters. This action opens the Global Parameters dialog box, which serves as your central hub for managing these parameters.
- Initiate New Parameter Creation: Within the Global Parameters dialog box, locate and click the New button. This will prompt a smaller "Parameter Properties" dialog box to appear.
- Define Parameter Properties:
- Name: Provide a descriptive name for your global parameter (e.g., Corridor_Width, Window_Sill_Height, Offset_from_Grid).
- Discipline: Choose the relevant discipline (e.g., Common, Architectural, Structural).
- Type of Parameter: Select the data type that matches the kind of information the parameter will store. Common types include:
- Length: For dimensions like heights, widths, or depths.
- Number: For quantities or ratios without units.
- Angle: For rotational values.
- Yes/No: For toggling boolean properties.
- Text: For non-numeric string values.
- Material: To link to material assets.
- Group parameter under: Assign it to a relevant grouping for organization within the Global Parameters dialog (e.g., Dimensions, Constraints, Other).
- Tooltip Description (Optional): Add a brief explanation of the parameter's purpose.
- Confirm Creation: Click OK to create the new global parameter. It will now appear in your Global Parameters list.
- Set Initial Value (Optional): Once created, you can set an initial value for the parameter directly in the Global Parameters dialog, or leave it blank to be driven by another parameter or formula.
Linking and Assigning Global Parameters to Model Elements
After creating your global parameter, the next crucial step is to link or "assign" it to specific instance or type parameters of elements in your model. This is how the global parameter exerts control.
There are two primary ways to assign a global parameter:
1. Linking to Instance Parameters
You can link a global parameter to an instance parameter of an element directly in the properties palette.
- Select Element: Choose the element in your model that has the instance parameter you wish to control (e.g., a wall, a door, a window).
- Open Properties Palette: In the Properties palette, locate the instance parameter you want to link. This could be a dimension (e.g., "Length," "Width," "Offset") or another type of property.
- Link Parameter Icon: To the right of the parameter's value field, you'll see a small gray button that looks like a tiny equal sign or a box. Click this button.
- Choose Global Parameter: A "Global Parameter" dialog will appear, listing all available global parameters of the compatible data type. Select the global parameter you want to link to and click OK.
- Observe Change: The instance parameter's value will now be driven by the selected global parameter, indicated by the icon turning blue. Any changes to the global parameter will update all linked instance parameters.
2. Linking to Type Parameters
Linking to type parameters means the global parameter will control that specific property for all instances of that family type.
- Select Element: Select an instance of the family whose type parameter you want to control.
- Edit Type: In the Properties palette, click Edit Type.
- Open Type Properties: In the Type Properties dialog, locate the type parameter you wish to link.
- Link Parameter Icon: Similar to instance parameters, click the link parameter icon next to the value field.
- Choose Global Parameter: From the "Global Parameter" dialog, select the appropriate global parameter and click OK.
- Confirm: Click OK on the Type Properties and Properties palette to apply the changes. Now, all instances of this family type will reflect the value of the linked global parameter for that specific property.
Example Scenario: Controlling Building Dimensions
Let's say you want to control the clear height of all corridor walls to a standard value across your project and also maintain a consistent offset for all building columns from a grid.
| Global Parameter Name | Type of Parameter | Linked To (Example) | Effect |
|---|---|---|---|
Standard_Corridor_Height |
Length | Instance Parameter: Unconnected Height (of Wall) | All walls linked to this global parameter will share the same height. |
Column_Offset_from_Grid |
Length | Type Parameter: Column Offset (within Family) | All columns of a specific type will maintain a consistent offset. |
Practical Insights and Benefits
- Centralized Control: Global parameters allow you to make sweeping design changes from a single location without having to edit individual elements.
- Design Intent Preservation: They help enforce design intent and relationships between elements, ensuring consistency.
- Formula-Driven Parameters: Global parameters can also be driven by formulas, allowing for complex relationships (e.g.,
Room_Width = Room_Length / 2). - Reporting Parameters: A global parameter can be set as a "reporting parameter" to read a dimension from the model and make that value available for other global parameters or formulas.
- Enhanced Parametric Modeling: They are fundamental for advanced parametric modeling workflows, making your Revit models more intelligent and adaptable.
By mastering the creation and assignment of global parameters, you can significantly streamline your Revit workflow, improve model accuracy, and maintain design consistency throughout your projects.
