Automatic mapping of BIM classification systems to IFC Predefined Types (predefined types) with ArchiCAD

In some technical forums, one sometimes hears claims about the limitations of IFC classes in their ability to classify BIM models in a sufficiently detailed manner. Added to this are certain limitations of some BIM modeling platforms in managing IFC Schemas. While it is true that certain disciplines, such as facilities, often require highly granular classification, these claims are not entirely true.In this sense, the objective of this pill is twofold and can be summarized as follows:

1. Show the depth in classification levels of elements of the IFC Schema itself.

2. Expose how ArchiCAD automates the process of mapping a BIM classification system to IFC Predefined Types.

1. IFC Classification Levels

First and foremost, it’s a good idea to understand the fundamental concepts of IFC Schema as a starting point. It’s an object-oriented technology, and its structure is based on so-called “classes” (also called Entities).

The different types of classes existing in the schema are organized hierarchically, each containing parameters related to their identification, behavior and different types of data. 

A certain class subtype will be the physical elements/components of the model (IfcProduct), which in turn can be subdivided, reaching the best-known entities such as, e.g., IfcSlab, IfcDoor, IfcFooting, etc.

The following sequence shows an example of the aforementioned hierarchical structure relative to a “beam” type construction element:

IfcRoot – IfcObject – IfcProduct –  IfcElement – IfcBuildingElement – ifcBeam

There are about 25 types of classes (entities) in the IFC 2×3 scheme corresponding to constructive elements of the model.

But this is not the final level of depth in terms of BIM element classification that the IFC scheme provides us.

Elements/components can belong to a specific family/typology, and each of them incorporates a series of attributes, such as those shown in the graphic, which ultimately make up the so-called Type. These type definitions refer to elements that have not yet been inserted into the model structure (they do not yet contain a specific location). They are used to specify the common elements that the different instances hosted in the project will share and that will already incorporate specific location data.

If we use the example of a horizontal compartmentalizing element, in IFC it would be classified as IfcSlab. Up to this point, all we have is a definition of a construction component that provides us with information regarding its shape and spatial relationship, but little else. If we want to delve deeper into the classification of said element, we will need to specify the specific subtype we need (is it a slab, false ceiling, landing, flat roof?).

To do this, the IFC Schema incorporates a series of attributes called Predefined Types , which can be related to the element/component level (occurrences) and/or their Types (Types), which add an enumerated list with an additional level of hierarchy that allows us to differentiate the element without the need to generate new entities.

If we follow the example of IfcSlab, referring to its Type (Type) IfcSlabType, we can obtain a list of values ​​(IfcSlabTypeEnum) like the following:

• Floor (default)

• Roof

• Landing

• Baseslab (slab or slab)

• Notdefined

• UserDefined: If a different type of value is needed than those included in the list, this is designated so that its value is annotated in another main attribute of the IFC Schema, called ObjectType.  

There are also other types of attributes of the same style that are also applicable to other types of elements such as doors or windows, for example, in which this additional level of classification may refer to aspects such as the material or the drive system.

 2. Mapping BIM Classification to IFC Predefined Types with ArchiCAD

For this classification to become an efficient workflow in our daily work, we need our BIM modeling tool to be able to access this editing level of the IFC Schema.

Here we briefly show you how ArchiCAD 21 allows this and also automates its mapping from standardized classification systems (Uniclass, Omniclass, Sfb…).

In this example, we use GuBIMclass V.1.2 ES ( www.gubimclass.org ), a BIM element classification system based on their primary function. Specifically, we will show the steps for assignment in the case of export. An automation can also be generated in the opposite direction (not explained in this article) when importing IFCs, so that they are automatically assigned to standard classification system codes based on the IFC types in the external model. 

In this example, we choose code 40.20.10.10. Interior false ceilings. We could proceed with each and every item in the classification system.

In certain projects where certain subtypes are very common, you can even assign a higher classification level and add the USERDEFINED option if you can’t find the element type you need. In this example, we’re introducing Acoustic False Ceiling as a more specific variant. 

Once we have configured our entire mapping system to the desired classification system, we can proceed to generate our IFCs, assigning the relevant MVDs and other configurations so that this task is fully automated in subsequent uses. However, this last part is already covered in later buildingSMART Spanish Chapters.

Conclusion

As we can see, the IFC framework also allows us to incorporate the necessary classification granularity into our models so that they can support the quality control or checking tasks required in our BIM processes.

Perhaps this way, the next time we have difficulties classifying models, we won’t have to blame the open IFC standard, which has become so accustomed to receiving all sorts of abuse, and we’ll have to look elsewhere for the source of the problem. 

Source: https://www.buildingsmart.es/2018/02/12/mapeado-autom%C3%A1tico-de-sistemas-de-clasificaci%C3%B3n-bim-a-tipos-predefinidos-ifc-predefined-types-con-archicad/ Like Share (0)