# Integrating BIM and GIS for an Existing Infrastructure
## 6 Discussion
The geometry in GIS is defined by surfaces (B-Rep), while in BIM, the object is defined as a solid (CSG) with the information contained in it [59; 60]. For this reason, the concept has evolved at the level of development in BIM. From a geometrical point of view, 3D BIM models are suitable for buildings or specific civil infrastructure such as bridges where all three XYZ dimensions are equally important, compared to the two-dimensional XY dimensionality of GIS. Therefore, linear infrastructure, where the XY dimension is predominant as opposed to the Z coordinate, has traditionally been managed using GIS tools. 3D GIS offers complete integration of BIM, covering buildings in a city, civil infrastructure across the landscape, and the structures and equipment contained therein. This allows managers to achieve an overall view of the infrastructure in an environment, facilitating decision-making and optimising available resources. This BIM-GIS integration has occurred mainly in the building industry, linked to the development of environments for smart cities, with very few cases for civil infrastructure. This may be due to the fact that the development of BIM in civil engineering is a step behind. In addition, applications focused on the modelling of linear infrastructure consider the terrain on which they are built, although they cannot carry out analysis of the environment in the same manner as GIS applications. Each technology has its own scale: micro in BIM and macro in GIS [1, 44]. The combined use of these two technologies enables a joint vision of the two domains, whether it is, for example, the urban environment for a building, or the landscape for infrastructure. The BIM-GIS integration will be useful in those phases of the LCA where this joint vision is necessary. BIM-GIS integration therefore involves developing a model to store, visualise, and analyse all available data on an asset and its environment. Semantic information is as important as, or more important than, geometric information, especially for the FM of the infrastructure. For this, it is necessary to maintain the full flow of information as much as possible. In addition, the efficiency of the management system depends on access to data outside modelling applications. The development of an application that meets the needs of infrastructure management, with access from any mobile device, is essential. The use of formats optimised for online access is also essential. Therefore, the use of the ISS format can be a good option for the development of a viewer that gives the user access to the entire scene surrounding the infrastructure. This can be generated from the corresponding scene layer package (SLPK) format, which can be generated from BIM models while maintaining the geographic and semantic information. The use of the ISS and SLPK formats represents a qualitative leap compared to the workflow used until now, i.e., the IFC to CityGML transformation. Although the ISS and SLPK formats are defined as standards, for now it is only possible to use them in the commercial applications of their developer company, with this being the great impediment to generalising their use. However, they are optimized formats for storing and sharing 3D GIS data from any device, either on the web or as local files [54, 55]. This is especially useful in the FM of assets, as it eliminates the dependence on specialized BIM software and facilitates the development of specific applications for each case. Therefore, research should delve deeper into the creation of these packages and scene services in the specifications of these standards. This article has shown a process of data integration for an existing road to optimise the resources available for its O&M. BIM and GIS technologies have been integrated to develop, together with a database, a web application focused on its FM. The aim was to generate a viewer using open standards to facilitate the interoperability of the data. Following the workflow shown in Figure 1, a 3D BIM model was developed from the available GIS data.