Modifying Linked IFC in Revit using C#: A Step-by-Step Guide

As a Revit developer, you’re likely familiar with the power of IFC (Industry Foundation Classes) files in facilitating collaboration and data exchange between different architectural, engineering, and construction (AEC) applications. However, when it comes to modifying linked IFC files in Revit using C#, things can get a bit tricky. Fear not, dear reader, for we’re about to dive into a comprehensive guide that will walk you through the process of modifying linked IFC files in Revit using C#.

Prerequisites

Before we begin, make sure you have the following prerequisites in place:

• Revit 2020 or later installed on your machine
• Visual Studio 2019 or later with the Revit API SDK installed
• A basic understanding of C# programming language
• An IFC file that you want to modify (don’t worry, we’ll provide an example)

Understanding IFC Files in Revit

Before we dive into modifying linked IFC files, it’s essential to understand how IFC files work in Revit. IFC files contain building information modeling (BIM) data that can be imported and exported between different AEC applications. In Revit, IFC files can be linked to a project, allowing you to reference and modify the data within the file.

When you link an IFC file to a Revit project, Revit creates a new instance of the IFC file within the project. This instance is known as an IFC linked element. The IFC linked element contains a reference to the original IFC file and allows you to access and modify the data within the file.

Loading the IFC File and Retrieving the Linked Element

Now that we’ve covered the basics, let’s load the IFC file and retrieve the linked element using C#. Create a new C# class library project in Visual Studio and add the following references:

using Autodesk.Revit.ApplicationServices;
using Autodesk.Revit.DB;
using Autodesk.Revit.DB.IFC;

In your main method, add the following code to load the IFC file and retrieve the linked element:

[Command("ModifyIFC")]
public class ModifyIFC : IExternalCommand
{
    public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements)
    {
        // Load the IFC file
        UIApplication uiApp = commandData.Application;
        Document doc = uiApp.ActiveDocument;
        IFCImportOptions ifcImportOptions = new IFCImportOptions();
        ifcImportOptions.IgnoreGeometry = true;
        doc.Import(ifcFile, ifcImportOptions);

        // Retrieve the linked element
        FilteredElementCollector collector = new FilteredElementCollector(doc);
        collector.OfClass(typeof(IFCImportInstance));
        IFCImportInstance ifcInstance = collector.FirstElement() as IFCImportInstance;
        IFCLinkedElement linkedElement = ifcInstance.GetLinkedElement();

        // Modify the linked element (we'll get to this part later)

        return Result.Succeeded;
    }
}

Modifying the Linked Element

Now that we’ve retrieved the linked element, it’s time to modify it. Let’s say we want to change the name of an element within the IFC file. We can do this by accessing the element’s properties and modifying the ‘Name’ property.

// Modify the linked element
using (Transaction transaction = new Transaction(doc, "Modify IFC Element"))
{
    transaction.Start();
    Element element = linkedElement.GetElement();
    element.get_Parameter(BuiltInParameter.ALL_MODEL_INSTANCE_NAME).Set("New Element Name");
    transaction.Commit();
}

In this example, we’re using a `Transaction` object to modify the element within the Revit database. We retrieve the `Element` object from the linked element and access its ‘Name’ property using the `get_Parameter` method. Finally, we set the new name using the `Set` method and commit the transaction.

Handling Complex IFC Data

In the previous example, we modified a simple property of an element within the IFC file. However, IFC files often contain complex data structures, such as hierarchical relationships between elements or Psets (property sets). To handle these complex data structures, we need to use the IFC API provided by Autodesk.

Let’s say we want to modify a Pset attached to an element within the IFC file. We can do this by accessing the Pset using the `GetPsetq` method and modifying its properties.

// Get the Pset
using (IFCModel ifcModel = new IFCModel(doc))
{
    IFCPSet pset = ifcModel.GetPsetq("MyPset");
    if (pset != null)
    {
        // Modify the Pset
        pset.SetProperty("MyProperty", "New Value");
    }
}

In this example, we create a new instance of the `IFCModel` class, which provides access to the IFC data within the Revit database. We then use the `GetPsetq` method to retrieve the Pset and modify its properties using the `SetProperty` method.

Saving the Modified IFC File

Once we’ve modified the linked element, it’s essential to save the changes back to the original IFC file. We can do this by using the `IFCExportOptions` class and specifying the export path.

// Save the modified IFC file
using (IFCExportOptions ifcExportOptions = new IFCExportOptions())
{
    ifcExportOptions.IncludeLinks = true;
    ifcExportOptions.FilePath = @"C:\Path\To\ModifiedIFCFile.ifc";
    doc.Export(ifcExportOptions);
}

In this example, we create a new instance of the `IFCExportOptions` class and specify the export path and file name. We then call the `Export` method, which exports the modified IFC file to the specified path.

Conclusion

In this article, we’ve covered the basics of modifying linked IFC files in Revit using C#. We’ve loaded the IFC file, retrieved the linked element, modified its properties, and saved the changes back to the original IFC file. With this knowledge, you can now automate and customize the process of modifying IFC files within Revit to suit your specific needs.

Best Practices

When working with IFC files in Revit, it’s essential to follow best practices to ensure data integrity and consistency. Here are a few tips to keep in mind:

• Always use the IFC API provided by Autodesk to access and modify IFC data.
• Use transactions to modify elements within the Revit database to ensure data consistency.
• Test your code thoroughly to ensure that it works as expected.
• Always save the modified IFC file to a new location to avoid overwriting the original file.

Troubleshooting Common Issues

When working with IFC files in Revit, you may encounter common issues such as:

Error	Solution
IFC file not loading	Check that the IFC file is valid and that the Revit API is properly installed.
Element not found	Check that the element exists in the IFC file and that the GetElement method is used correctly.
Pset not found	Check that the Pset exists in the IFC file and that the GetPsetq method is used correctly.

By following the guidelines outlined in this article, you should be able to successfully modify linked IFC files in Revit using C#. Happy coding!

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