# Innovative System for BIM/GIS Integration in the Context of Urban Sustainability
## 3 Materials and Methods
### BIM and GIS Integration through an Experimental VR/AR/MR App  
To try to overcome the challenges of the prior solution, a feasible alternative is to use mixed, augmented, and virtual immersive reality. Concerning this, an app suitably implemented by the authors is proposed, also useful for remote inspection and virtual consultation. The aim of this app focuses on digitizing information and making it available at any time, as well as using innovative methodologies such as VR/AR/MR for visualizing 3D models and other relevant data. Moreover, with the aim to propose a solution to the unification of BIM and GIS data, the app has been implemented in such a way that the three-dimensional model of the building can be viewed in VR/AR/MR both in situ and remotely: the information contained in the model is displayed by activating the GPS coordinates or when the device recognizes the identifier of the building in question in the geospatial map, allowing for remote viewing of the hologram in any environment.  
For app creation, there are several platforms and tools available, each with special capabilities leading to important advantages. For this investigation, the Unity 3D platform was selected [44; 45], through which it was possible to develop the app by adding and controlling components with Unity's user interface (UI) system. In order to provide an immersive and engaging experience, it was decided to use the Microsoft HoloLens viewer in addition to the app [46; 47]. With the help of this kind of wearable viewer, which combines interactive virtual elements with the real world, users may interact with three-dimensional digital content inside their physical surroundings. Unity 3D 2021.3 allows for great visualization and the possibility to observe and manipulate 3D models as if they were actual objects inside the virtual scene. The device also includes an on-board processing unit (HPU) that handles data processing and motion tracking to enable precise and smooth interactions. Figure 5 shows the flowchart of the methodology to create the app.  
Figure 4: Revit model import stage.  
The app's implementation shows the building's 3D model as a holographic image overlaid on the field of view regardless of whether the user is in the area or whether the device running the app is close to the building in question and can identify the building's ID from a GIS map. To do this, a user who wants to view the model when they are near the building will need to decide regarding the activation of the device's GPS to define the spatial range for identifying additional models and analyzed case studies. When the user decides to turn on the GPS, the application will create a 10 km radius around their current position and plot any pertinent case studies on the map. The application offers the user the choice to see the 3D model, user interaction labels, and device for presenting information or 3D in virtual reality (VR) if they are within this range.  
In this scenario, the camera must be turned on, allowing for the 3D model to be superimposed, thus making it visible. Alternatively, if the user does not activate the GPS, the augmented reality (AR) information and the view of the 3D model in VR will occur directly through camera framing. The VR/AR/MR app is certainly advantageous for an immediate and immersive visualization and allows for planners and managing bodies to make decisions supported by more detailed and complete information. The main disadvantage is not being able to carry out purely analytical analyses, which could instead be fundamental in some situations concerning the monitoring or the planning of interventions. Below, in Figure 6, we present a flowchart highlighting the app process implementation and its logical stream.  
Figure 5: Flowchart of the app’s development with Unity.  
Figure 6: Logical stream of the VR/AR/MR app’s implementation.