Basics of IFC based model exchange - Export

[Szabolcs Miko]

Archicad supports the OpenBIM concept, using a common language available for software vendors. This widely-used file format, known as IFC (Industry Foundation Classes), was developed by buildingSmart®. Read more about IFC on buildingSmart's web page.

Model filtering

Model filtering is what we start with. Setting up the 3D view, containing all the data (and only the data) that is required by the other disciplines is just as important as the information stored in the elements. What are our filtering options in a 3D view?

• Partial Structural Display for showing and hiding finishes, other and core materials
• Filter and Cut elements in 3D to hide specific element types (based on element hierarchy)
• Renovation Filter is also an option, if the export is about a specific design phase
• IFC Model Filter in Translator Settings
• Layer Combinations to separate elements logically

Combine these options, depending on the export requirements, to get the best and easiest result.

Geometry

Native Archicad elements can be carried as both Extruded/Revolved and BREP (Boundary Representation) geometry. We choose this depending on the disciplines, we send our model to. What is the difference between these two? Extruded/Revolved elements are parametric, their geometry is based on vectors and profiles, rotated around an axis or extruded by a specified distance normal, for example Archicad's Wall, Beam or Column elements. On the other hand Boundary Representation elements are build up by nodes and faces, similar to how our Morph elements are. What should we export? The exported IFC file should depend on the discipline we send it to. In a simple scenario: Extruded/revolved: From a structural engineers point of view finishes, doors, windows are probably irrelevant, but they could use other parts of the model (columns, beams, slabs, walls with openings, footing etc.) as extruded elements, for structural analysis and calculations. BREP: MEP engineers wouldn't benefit from extruded/revolved elements, what they need is the exact geometry. (Note: Usually the structural engineers use the architects structural model as a reference, but model the geometry in their own environment. Such a scenario but be better supported by exchanging BREP geometries.) Where can we set this? Read more about how to set up the Geometry conversion for IFC Translators.

Type mapping

What is Type mapping? For this we need to know of what are Archicad Classifications and what the difference is between an Element Type and an Element's Classification. This is important because an element's Property set is based in the element's classification. The Property Availability for Classifications can be set in the Property Manager.

During IFC export Type mapping assigns IFC types to the exported elements based on their Archicad classifications, according to the requirements of the receiving parties or disciplines. Read more about how to set up the Type Mapping for IFC Export.

Property mapping

Property Mapping assigns IFC properties to elements based on the IFC Types previously received from the IFC Type Mapping for export. The standard ARCHICAD Classification system comes with a predefined property mapping table. Read more about how to set up the Property mapping for IFC Export

Model coordination

ARCHICAD Coordinates

• Project Origin - the 0;0;0 of the project's coordinate system
• User Origin - by default it is located at the Project Origin, but it can be moved to any location, allowing you to use an alternative 0;0;0 for calculations and input
• Hidden Origin - if the model content is far from the Project Origin, it is generated in the background for more accurate calculations

Read more about Origins

Model Location

Coordinating model data coming from different stakeholders and software isn't the easiest task, but can be solved by following a common agreement in coordinates. There are two main approaches for modelling:

Local Coordinates

Modelling in Local coordinates means that we are close to the Project Origin and our model isn't rotated to North. This is the easiest, most common and the recommended workflow for architects.

World Coordinates

Modelling in Real World Coordinates means to place the model where and how it would stand in real life. In this case, the origin is a defined point with an x,y and z value and the model receives it's coordinates based on this reference, rotated to it's true north

Survey Point

Starting from AC20, in the Object Library there is an object called the Survey Point Object. It was developed to support the workflow of modelling at local coordinates. Instead of placing the model far from origin, we can place the Survey Point Object where the 0,0,0 of the exported file should be. Look for the related Settings under File/Interoperability/IFC/IFC Translators.

Data Conversion

In this dialog it is possible to define (in addition to element geometry) which data should be exported to IFC. This can be useful in data exchange with facility management, energy analysis or cost estimation programs. Read more about Data Conversion for IFC Export Read more about the Translators for Export (Detailed Settings). If we talk about OpenBIM and support the IFC based data exchange, which gives the best interoperability results, we don’t have to deal with RVT and RFA files at all. Yet, in case it happens, read more about Model exchange with Autodesk Revit®