# An Inspection of IFC Models from Practice
## 2 Industry Foundation Classes
### IFC Georeferencing  
Despite some increased use, georeferencing is still not a common practice among building designers, for whose aims a local system is usually preferable, implying the use of Cartesian coordinates with small and more manageable values. Building Information Modelling software works better as well with such close-to-origin Cartesian coordinates, as the precision of floating point numbers is dependent on their distance from the origin. However, properly georeferencing an IFC file makes it possible to link the (local) coordinates inside an IFC model with the corresponding coordinates of the real-world location, and thus to place the model of a single building or construction within its planned context, related to other existing and planned objects and any relevant environmental factors. For this reason, more and more studies address the need for georeferencing BIM and storing such information in the IFC files themselves [28; 29; 30], including by a buildingSMART working group ([[https://www.buildingsmart.org/wp-content/uploads/2020/02/User-Guide-for-Geo-referencing-in-IFC-v2.0.pdf](https://www.buildingsmart.org/wp-content/uploads/2020/02/User-Guide-for-Geo-referencing-in-IFC-v2.0.pdf)]([https://www.buildingsmart.org/wp-content/uploads/2020/02/User-Guide-for-Geo-referencing-in-IFC-v2.0.pdf](https://www.buildingsmart.org/wp-content/uploads/2020/02/User-Guide-for-Geo-referencing-in-IFC-v2.0.pdf)), accessed on 1 March 2021). There are several options to store georeferencing information in IFC, as described by [PERSON] and [PERSON] [31]. These options range from basic address information to the definition of a more detailed position referred to a projected coordinate reference system (CRS). In this last case, an offset can be stored between the project coordinate system and the global origin of a CRS (\(X\), \(Y\) and height). The rotation of the \(XY\)-plane is also included (Table 1). However, those levels do not necessarily indicate a scale measuring the quality of georeferencing, but they are mostly relevant to identify how the information is stored. In fact, in some cases, the accuracy of different _LoGeoRefs_ can be absolutely similar (e.g., _LoGeoRef30_ and _LoGeoRef40_), since the values are supposed to be the same, but stored differently within the IFC file. A further note is useful about the storage of the model reference system direction. In the _LoGeoRef40_ the stored direction represents the _TrueNorth_ ([[https://standards.buildingsmart.org/IFC/RELEASE/IFC2x2/FINAL/HTML/ifcrepresentationresource/lexical/ifcgeometricrepresentationcontext.html](https://standards.buildingsmart.org/IFC/RELEASE/IFC2x2/FINAL/HTML/ifcrepresentationresource/lexical/ifcgeometricrepresentationcontext.html)]([https://standards.buildingsmart.org/IFC/RELEASE/IFC2x2/FINAL/HTML/ifcrepresentationresource/lexical/ifcgeometricrepresentationcontext.html](https://standards.buildingsmart.org/IFC/RELEASE/IFC2x2/FINAL/HTML/ifcrepresentationresource/lexical/ifcgeometricrepresentationcontext.html)), accessed on 1 March 2021) attribute, defined as \"direction of the true north relative to the world coordinate system as established by the representation context\". As also cited in the buildingSMART document about georeferencing ([[https://www.buildingsmart.org/wp-content/uploads/2020/02/User-Guide-for-Geo-referencing-in-IFC-v2.0.pdf](https://www.buildingsmart.org/wp-content/uploads/2020/02/User-Guide-for-Geo-referencing-in-IFC-v2.0.pdf)]([https://www.buildingsmart.org/wp-content/uploads/2020/02/User-Guide-for-Geo-referencing-in-IFC-v2.0.pdf](https://www.buildingsmart.org/wp-content/uploads/2020/02/User-Guide-for-Geo-referencing-in-IFC-v2.0.pdf)), accessed on 1 March 2021), this could be different from the grid North, considering a Cartesian system and possibly stored as part of the _IfcObjectPlacement_ within _IfcSite_ (inherited from the class _IfcSpatialStructureElement_ and, in turn, _IfcProduct_), according to _LoGeoRef30_.