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IFC Models

What is the IFC Format?

IFC (Industry Foundation Classes) is an open standard for exchanging BIM data (Building Information Modeling). The format is developed by buildingSMART and is used to share models between different software without being locked to one system.

Info

See the buildingSMART website for more information.

The IFC initiative started in 1994, and the first version was released in 1997. IFC is a non-proprietary, neutral data format. IFC is a comprehensive and complex schema that contains objects, properties, relationships, geometry, and data.

IFC was originally a standardized digital description for buildings, but has also gained support for infrastructure.

IFC model example

Example of an IFC model

In September 2023, IFC 4x3 was released, and the main purpose of IFC 4x3 has been to extend the IFC schema to cover the description of infrastructure within discipline models for roads, bridges, railways, etc.

Why is IFC Important?

  • Interoperability: Ensures that models can be shared across different software
  • Open standard: Not proprietary, free from licensing restrictions
  • Rich information: Contains both geometry and metadata (materials, properties, classifications)

How is IFC Structured?

IFC has a hierarchical structure. Example for buildings:

  • Project
  • Site
  • Building
  • Storey
  • Elements (walls, doors, windows, etc.)

IFC is object-based, where each element has properties and relationships. The format supports geometry and coordinates through local coordinate systems as well as global georeferencing.

IFC Versions

IFC 2x3

Most widely used version today, but older. Limited support for infrastructure and georeferencing.

IFC 4 and 4x3

Newer versions with better support for infrastructure such as roads, bridges, and more precise georeferencing.

Limitations and Pitfalls

  • Not all programs interpret IFC the same way, which can result in visual discrepancies
  • Large files can be heavy to handle
  • Differences in georeferencing between versions can result in different behavior

Use Cases in Gemini

Through the DDSCad platform, we get general IFC support for IFC 4x3. These IFC files can be referenced into the drawing in the same way as we do today for IFC 2x3/IFC 4 and harvest survey data from them to an application layer.

IFC-Building

Support for IFC-Building allows us, for example, to insert houses that are constructed in other architectural packages that support this standard, and get sensible material choices for 3D presentation. Buildings drawn in AutoCAD ADT, ArchiCAD, etc., we recommend exchanging with the IFC format.

From the inserted IFC files, we can harvest survey data to application layers. An application layer is a general storage structure for geometry and attributes. It gives the user the ability to store many types of geographic data within its structure.

Infrastructure with IFC 2x3

When it comes to infrastructure, IFC 2x3 has typically been used for certain discipline models such as roads and bridges. This has been solved, for example, by using a class for non-standardized elements, ifcBuildingElementProxy, and general PSet for information. The problem has especially been survey data (points and lines), as available geometry has been a limiting factor.

IFC 4x3 for Infrastructure

With IFC 4x3, however, we have gained the ability to break down infrastructure using new classes, such as ifcRoad. ifcRoad in turn has classes such as ifcRoadPart, ifcPavement, etc. In other words, we can now describe the discipline model for roads in a standardized way that everyone can relate to.

A fundamental difference between a building and a road is the area they occupy. Buildings can be several hundred meters tall, while infrastructure can be kilometers long.

An important concept in IFC 4.3 is therefore alignment (horizontal curvature, vertical curvature). Alignment or centerline defines a reference system for placed elements in infrastructure projects, while in buildings, only project coordinate systems are used where all elements get their XYZ coordinate in space.

IFC 4.3 also has an information element, ifcAnnotation, which can be used to convey important information in the form of survey data to surveyors. ifcAnnotation can be, for example, points and 3D lines.

Data Flow to SFI Model

We therefore have a dedicated function for data flow between IFC 4x3 Road and our own SFI model. What is new in this context, is that we now import data directly to the SFI model.

An SFI model is a storage structure adapted to infrastructure models such as roads, tunnels, and trenches. Both application layers and models support information, such as PSet in IFC.

Methods for Adding IFC Files

We can add IFC files directly or dynamically (manual placement) to the model list via three different alternatives:

  1. Georeferenced IFC model - The model will position itself correctly in the map with Add...

  2. IFC model with coordinates for zero point in the project - We must first enter the project origin in Gemini Terrain under Gemini Terrain Settings... - Project - IFC, and then insert it into the drawing with Add...

  3. IFC model only with true north direction - We must georeference the model manually after first inserting it into the drawing with Add... or Add Dynamically...