## 4 Method
### Information Sharing: Transforming 3D Survey and HBIM Models in XR Projects
#### 4.5.1 HBIM Interoperability for eXtended Reality (XR): From HBIM Models to Virtual Reality
Therefore, Blueprint is a system built into Unreal Engine 4 that allows you to visually create game scripts by linking nodes, events and functions. The types of Blueprints that were first developed are Level Blueprints and Blueprint Classes, but there are also Blueprint Macros and Blueprint Interfaces (Figure 11). Furthermore, for the case study of the Church of San Valentino, it was possible to go beyond the potential offered by the basic architecture of the software, creating and applying a sustainable workflow able to work simulated with Mc Neel Rhinoceros, Autodesk Revit, Twinmotion and Unreal Engine. Thanks to a completely open development logic, migrating the Twinmotion project to Unreal Engine and increasing the project's level of interactivity through the VPL. In particular, the user, both in the first and third person and through different devices, can interact with the digitised objects, reading and discovering descriptions and information relating to the paintings of the church, its historical background and the cultural context in which it is situated. Moreover, thanks to the project's correct georeference, it was possible to tell the surrounding environment in a more interactive form and reach a total immersion where the user, through a VR headset, joystick or keyboard, can freely navigate and interact with IVO. This phase was supported by the development of specific VPLs which can create objects from a scan-to-BIM process (Figure 12). Finally, a further development phase made it possible to increase the level of interactivity of the project to the maximum permitted levels. Thanks to the creation of content associated with a specific QR code, it was possible to connect VR with an AR object library. The implementation phase from VR to AR involved the creation of a library of objects that can be implemented over time, where the end-user, while immersing himself in the VR project, can increase his perception and knowledge of the contents and architectural and structural elements of the church through forms of AR such as mobile and tablet. Figure 11: The main Visual Programming Language (VPL) in Unreal Engine implemented and used for the development of the VR app of the research case study. 5.2 Augmented Reality for Built Heritage: Towards Augmented Information of Interactive Virtual Object Library  
The HBIM approach can be used in AR for many purposes. For example, in the case of the Church of San Valentino, AR tech can serve as a tool that enables the visitors of this place to interact with the church on an immersive level, getting acquainted with the local cultural heritage. To create an AR experience, one must always prepare the most accurate 3D model possible. Our professional expertise indicates photogrammetry to be the best approach when it comes to choosing the source the 3D models should be built upon. Since the HBIM approach relies on a detailed depiction of a structure, there are multiple rules to follow while the transition of 3D models between an artist and a developer occurs. Such things as Geometry/Topology, 3D Model Scale, 3D Model Centering at Origin, Placement, 3D Model Reset Orientation and Scale Transforms, Scene Organisation, Textures and Materials, Rigging, Source Delivery, and File Formats, Animation should be taken into account. Moreover, the HBIM approach implies the visualisation of a mathematical model with a vast quantity of data interconnections in it. This abundance of infrastructure inside a model affects its size and makes it a high polygon model. Since most devices with AR capabilities were designed to show low polygon structures, a thorough redrawing of a sophisticated HBIM mesh is in order. In other words, one needs to throw away all  
Figure 12: The level of synchronisation obtained between the various software applications and VR devices. unnecessary calculations and over detalisation created by the HBIM approach to put the same model into AR. High polygon meshes require more time to be loaded into the AR.