## 3 State-of-the-Art
Thanks to the parametricity, it was possible to connect a large amount of data and information to each single 3D parametric object, improving the utility and the quality of HBIM models for different purposes [27,31,32]. Therefore, the arduous task of the scan-to-BIM process was to bring a significant amount of data, such as 3D scans, photographs, historical research documents, material and decay analysis, into 3D parametric objects and BIM databases (information mapping) [33,34]. Therefore, overcoming this commercial and informatic gap was necessary to increase the knowledge of digital analysis that required BIM, such as energy analysis, finite element analysis, MEP planning, scheduling, and cost estimation. This concept could be seen as the knowledge related to the concept of interoperability (second requirement) [7,35]. Each type of software needs different kinds of formats, and therefore each BIM needs transfer requirements that allow different levels of interoperability for post-analysis uses [36]. Consequently, it was clear that the quality of a scan-to-BIM model was fundamental at the beginning of the generative process. Furthermore, the orientation (third requirement) itself must be based on new levels of interoperability between different types of software and exchange formats. In this context, it was evident that modelling was the primary factor to be investigated to reduce and manage the gap between model and information sharing [3]. Accordingly, to go beyond an HBIM and represent the architecture in increasingly intelligent and innovative forms capable of interacting with the final users. For this reason, in recent years, research has focused on improving the operational and methodological aspects of HBIM and its metric, historical and cultural value through virtual interactivity (fourth requirement), improving the relationship between models and users [5,37]. In this context, VR is made up of technological and experiential factors capable of bringing the user to new forms of digital experience, going beyond the limits of BIM and other forms of 3D static representations [38,39,40]. Concerning the experiential aspect, VR represents a radical change within the media experience: the subject from the observer of an action becomes the protagonist. VR was born from the idea of \"replicating\" reality as accurately as possible from a visual, auditory, tactile and even olfactory point of view to perform actions in virtual space overcoming physical, economic and safety limits [40]. The subject is projected into alternative digital worlds, experiencing first- and third-person adventures. Manipulating, seeing, hearing, touching virtual objects, travelling through spaces without a place induces an active interaction process with the virtual world, producing a sense of presence, that is, the sensation of being in the virtual environment. On the other hand, AR is the representation of an altered reality in which virtual/artificial sensory information is superimposed on the ordinary reality perceived through our senses [41]. It is a perceptual enhancement, fundamentally based on the generation of virtual contents by a computer and their superimposition with reality [42]. From a technological perspective, VR consists of a series of tools capable of obtaining information on the subject's actions (input tools), which are integrated and updated in real-time by the computer to build a 3D world. Based on the output tools used, it is possible to distinguish three types of VR:  
Non-Immersive: determined by a monitor that acts as a \"window\" through which the user sees the world in 3D; interaction with the virtual world can be done through the mouse, the joystick or other peripherals such as gloves. Semi-Immersive: determined by rooms equipped with devices and surround rear-projection screens that reproduce the stereoscopic images of the computer and project them on the walls, with different shapes and degrees of convexity, suitable indices of the depth of the image, giving the so-called effect three-dimensional.