IFC Made Easy15 Sep, 2011 By: Matthew Brewster
ArchiCAD Insights Tutorial: An IFC file is the best solution for transferring BIM models — but what is it?
Editor's note: This tutorial courtesy of Graphisoft.
Because more firms are embracing BIM (building information modeling) as their preferred design tool, questions are arising about how to work together more efficiently. As the old standards of DWG and PDF exchange are slowly fading away, BIM offers a better exchange of information allowing the exchange of intelligent 3D data. This is obviously more valuable as the data is being used for things such as energy analysis and facilities management. So what is the best way to exchange this data with the people you work with? The new standard is evolving around IFCs.
But what the heck is an IFC? While various BIM applications have their own file formats, there is a universal format that allows these applications to talk to each other. IFC (Industry Foundation Classes) is a vendor-neutral file format that handles the information in a BIM model. With IFC, you can use your BIM of choice and have the confidence that your files will be compatible with minimal effort. There is no longer any need to worry about which software your consultants are using.
When you transfer information with an IFC file, walls remain walls, doors remain doors, etc. Material and 2D data can be transferred with this file format as well, but it is really the 3D model and underlying data that makes it the best solution for transferring BIM models. In addition, IFC further extends the data in model elements. For instance, an ArchiCAD wall contains information regarding size and shape, structure and finish. The IFC data can add information such as fire rating, manufacturer, reinforcement, etc. This data becomes part of the BIM model and is transferred through the IFC exchange.
Communication is key to a good translation. Before saving a model as an IFC, it is important to know what data is needed by your colleague and to filter your model accordingly. You can use ArchiCAD's layer controls for this first step; simply turn the appropriate layers on and off with the Layer Manager. It is a good idea to save a Layer Combination so you can return to this model state at any time.
You can also fine-tune the specific portions of structural elements that will be transferred. Partial Structure Display controls what portions of Composites and Profiles are displayed. For instance, when viewing a wall in an architectural model, you want to see the structure and finishes. However, when you send it to your engineer, you want to turn off the finishes to show just the load-bearing core. Doors and windows can also be turned off so that only the openings are shown in a structural model.
Now that your model displays the information you want to transfer, you are ready to save it as an IFC. In ArchiCAD 15, you can do this with a "one-click export." Go to the File menu and select Save as, choosing IFC 2x3 file as the format. If you are saving from the floor plan, you have four Export options: Visible elements (on all stories), Visible elements on current story, All elements on current story, or Entire project. Choosing Visible elements (on all stories) in a 3D window view, you export what you see on the screen.
Now choose your Translator. This is where you pick the software that your consultant is using. (Of course you can also create new translators, or customize predefined ones.) Click Save and the Translator will create an optimized IFC file based on the chosen application.
Before you send off the IFC file, it is a good idea to check it with an IFC viewer. This ensures that you are sending the data you intended to share. Solibri makes a great viewer that is freely available and runs on Mac or Windows.
Note that IFC files tend to be larger than their ArchiCAD counterparts (because there is some redundancy in the IFC file, and ArchiCAD files are highly efficient). Solibri also makes an IFC Optimizer that can reduce the file size by about 90%, making file transfer and the opening process much faster.
For the return-trip process, Graphisoft has developed an Add-In for Autodesk Revit Structure and MEP. This improves both the IFC export and import of Revit with a button added to the Revit Add-Ins ribbon. Revit users can simply click the Improve IFC Exchange button for the bidirectional IFC model transfer. This free Add-In (together with another that enables "one-click" export of HVAC elements only from Autodesk Revit MEP) are available from www.graphisoft.com/support/archicad/downloads/interoperability.
When bringing files back into ArchiCAD, you have a few options. One approach is to open the IFC file and save it as an independent ArchiCAD file. This will import the BIM elements into their native ArchiCAD counterparts. (Note that the Translator is available during the import process as well.) You then hotlink the saved file into your ArchiCAD project. While this is a good strategy for large BIM models, it is becoming less of an issue thanks to 64-bit and multiprocessor support in ArchiCAD 15. In addition, Graphisoft has improved the performance of the IFC import and export process with the latest release.
Another option is to merge the IFC file into your current ArchiCAD project. You can choose to bring in the entire content of the IFC model, or a filtered part of it (filtration by story, by element type, by domain, etc.). This way you can avoid duplicates of your architectural elements. The engineer's model can be placed on a separate "locked" layer to keep the elements separate, similar to a referenced model. Additional attributes such as profiles and materials (defined by the engineer) will also be available in your project.
What happens when you receive an updated file from your consultant? How do you know what changed? To address this, Graphisoft has enabled ArchiCAD to detect the changes between two versions of the same project. To do this, use the Detect IFC Model Changes command found under File > File Special > IFC 2x3. You select the older and newer versions of the incoming IFC file; the changes between the two files will be automatically detected and highlighted using ArchiCAD's Mark-Up Tools.