# Innovative System for BIM/GIS Integration in the Context of Urban Sustainability
## 2 Background
Although this technology has shown great promise, there is currently a dearth of knowledge on its integration with 3D models (BIM or restitutions from Lidar, laser scanner, or drone survey) [34; 35]. Despite that, Cesium is another system that makes use of 4D, or three spatial dimensions plus time. It is capable of detecting moving objects, displaying environmental changes, and handling time-varying data, such as those from satellite or drone photography. The applications of this system are numerous, like tracking traffic patterns, natural disasters, and urban development. An important field for geospatial research and visualizations is, in fact, 4D geospatial data. The significance of 4D web-based geographic information systems (WebGIS) for displaying time-varying geospatial data, for example, is discussed by [PERSON], [PERSON] et al. [36], especially for educating decision-makers about coastal development. In their paper, authors draw attention to the difficulties in integrating temporal data into web-based geovisualization tools and the necessity of a good user-friendly interface to prevent extremely abstract (aleatory) and difficult-to-understand representations. [PERSON] [37] instead concentrates on the creation of geosimulation techniques for simulating the spatiotemporal dynamics of changes in 4D vertical urban growth, demonstrating the importance of 4D geospatial data in the development and advancement of UP for sustainable cities. In this framework, the proposed research focuses on the construction of the 3D model of a building in BIM (Autodesk Revit) starting from the initial phase of the survey and its subsequent integration into the GIS (ArcGIS) through the commercial software Autodesk Infraworks, highlighting the pros and cons of its use. Subsequently, the information available is managed through a suitable experimental app created by the authors, highlighting the advantages that it offers both to the user and to the manager. The app obviously makes it possible to solve the problem of integration exclusively from the point of view of visualization, since it is precisely a matter of virtual reality, but it has numerous advantages related to its practical use, as well as the commercial software which, while allowing for the correct visualization of the BIM element in a georeferenced environment, still does not allow for complete integration due to the loss of information during the transfer of the 3D model to the GIS environment. For this reason, a strategy, still under study, is proposed through which it is possible to use the open-source platform Cesium ion to better integrate 3D data in a multi-layer environment, to build an interactive 3D-4D geospatial map. The proposed solution consists in adding to the standard primitives present in the Cesium libraries a software module (JavaScript), suitably implemented, capable of converting the IFC file of the BIM model into a compatible file to be then displayed in CesiumJS (geospatial layer viewer). Although there may still be several problems still present today in relation to the transfer of IFC files to CityGML, the method seems to be very promising, allowing for temporal visualizations. Other examples of customizable libraries will also be proposed, such as that of deck.gl, which is newer than Cesium. The present work, therefore, clearly aims to emphasize the innovative aspects of the integration of these two technologies, highlighting how this integration contributes to the advancement in theoretical and practical knowledge on digital twin technologies. The innovation of the system lies in showing the methodology to create a complete, free, and open-source system useful for the urban planning of sustainable cities.