## 1 Introduction  
In the last few years, the construction sector has benefited from the advent of the latest generation techniques, methods and tools in the fields of 3D survey, modelling, visualisation and computer graphics. The results obtained from a scientific methodological approach based on integrating the 3D survey, digital photogrammetry with the building information modelling (BIM) allowed professionals to define a new research-oriented field to manage and preserve heritage buildings and archaeological sites [1]. This approach, known as the scan-to-BIM process, used applied research capable of addressing and solving various technical, information technology (IT) and operational problems for the digital management of complex artefacts such as monuments, castles, infrastructures and churches [2; 3; 4; 5]. Heritage buildings from a strictly geometric, metric, and informative perspective are characterised by complex architectural and structural elements that cannot be represented appropriately through the leading BIM software such as Autodesk Revit and Graphisoft Archical. This first obstacle has now been overcome for some years both from the topological and morphological perspectives. Interesting studies [6; 7; 8; 9] have integrated and automated the digitisation process of artefacts of high historical and cultural value thanks to the development of scan-to-BIM modelling requirements, methods and techniques capable of maintaining the bidirectional information-object relationship within the BIM project. Consequently, applied research in this specific context has shown how to orient and implement the BIM process for artefacts that require the transmission of different information compared to new buildings [10; 11; 12]. In particular, heritage building information modelling (HBIM) projects has made it possible to archive, compute, map and share different types of information connected to digital models such as material, historical and decay analyses to improve the conservation and preservation process of the artefact [13; 14; 15]. Computing, information mapping and sharing were determining factors to understand the main differences compared to CAD vector representations that have characterised the architectural representation in the last three decades [16; 17]. Given these three factors, consequently, the term interoperability linked to digital models became a very active field of development and research [3; 11; 18; 19; 20]. The development of exchange schemes and formats (proprietary and open) such as DWG, IFC and FBX have been improved to enhance the transmission of information, enhance the dialogue between the main post-processing, modelling and BIM software. On the other hand, in recent years, the advent and implementation of open platforms oriented towards eXtended Reality (XR) have opened a new path of IT development that can also be followed by architects, engineers and professionals in the construction sector in general. Furthermore, the growing need to share information in increasingly innovative, intelligent and direct forms such as Virtual and Augmented Reality (VR-AR) has led to the launch of a new phase of research and development. Some studies [14; 21; 22] have shown how professionals can increase the usefulness of HBIM models and the scan-to-BIM process through computer languages such as the Visual Programming Language (VPL). For those reasons, this article summarises the results and developments oriented to creating XR projects based on new forms of human-computer interaction, data collection, scan-to-BIM process and digital photogrammetry for the Church of San Valentino, Siusi, Italy. The article deals with and analyses in a first phase an updated state of the art in the field of HBIM and XR. The authors deepen both from the theoretical and practical point of view Virtual Reality (VR) and Augmented Reality (AR) oriented to the sharing of information in the field of built heritage.