# Integrating BIM and GIS for an Existing Infrastructure
## 6 Discussion  
Vast areas of industry are undergoing a period of digital transformation, supported by the development of ICT. The AECO sector is usually more reticent when it comes to applying new technologies, but it is no stranger to this transformation. Both BIM and GIS are part of these data-driven technologies, and in both cases, information management and visualisation play a key role [1]. However, their approaches to dealing with data are different. On the one hand, GIS were born from geographic science, being more technologically mature than BIM. Traditionally, these systems have been used for territorial analysis, so the scope of work has been 2D at large scales. More recently, 3D GIS has begun to  
Figure 5: Infrastructure scene. develop thanks to the development of applications that can represent three-dimensional environments, which has been quickly adopted in the representation of cities [42; 45]. On the other hand, BIM was developed as a way of unifying all the documentation available on a project [21]. One of its greatest virtues is access to information through a 3D model, through which the greatest possible level of detail could be obtained. In terms of standardisation, GIS has consistently been characterised by its open-source aspect. This has meant that, although there are a multitude of formats associated with GIS, most of them are standard. Furthermore, most of these formats are operable by a few applications. Although the main technological advances in GIS, such as the implementation of 3D, are found in a few commercial applications, there are free applications capable of performing most GIS functions [3; 48; 54]. This has led many public administrations to publish their data under this framework. However, there is hardly any legislation on the implementation of GIS, limited to the regulation of data transfer. On the other hand, BIM has been characterised by a technological race in which numerous commercial applications have been developed, each with their own formats [34]. Great efforts have been made towards standardisation, and the IFC format has become the most important one for the transfer of models. However, the use of this open format implies a loss of semantic information [33; 35; 36]. Nevertheless, governments have started to propose and regulate the use of BIM in public contracts. BIM-GIS integration in the AECO sector brings with it several opportunities. Both technologies are data-driven, and this is one of the critical links between the two technologies, which can be complemented by an external DB. The DB holds all up-to-date and accessible information, including data that do not necessarily need to be included in the 3D model. This makes it possible to lighten the content of the model, facilitating its use from any device and avoiding the modification of the model for non-geometric updates. On the other hand, it is possible to apply technologies such as IoT or AI by keeping the information segregated and organised in the DB, favouring the efficiency of the infrastructure management systems and easing the FM of the infrastructure through its DT. In this case, access to the DB and the model must be accomplished with proprietary management applications, which allows implementing the functionalities required for each infrastructure. These applications can be designed and adapted to each of the needs by providing simple and intuitive interfaces that can be used by the technical staff dedicated to the O&M of the infrastructure. Another linking point is 3D integration. Most authors have assessed BIM-GIS interoperability using the IFC-CityGML formula. This implies a loss of semantic information due to the use of both formats. Moreover, there is a loss of geometric information [1; 7; 61]. This is where the level of detail comes in. This is a common concept in both technologies, but with a different meaning. The way in which the 3D element is modelled is key.