# AR in the Architecture Domain: State of the Art
## 1 Introduction
The selection proposed in Figure 1 is a qualitative analysis based both on the contents and descriptions of the different ERC panels, and on the author's experience. There is, therefore, the awareness that many of the fields not mentioned may play a role in this tree structure. However, the scheme intends to show the fragmentation of the disciplinary fields involved in AR for built architecture for skills and research content. The cultural, social, and content aspects are mainly supported by the social sciences and humanities (SSH). In contrast, hardware, software, and algorithmic aspects are analyzed more in the physical sciences and engineering (PE). In the SSH domain, there is a more significant sector fragmentation related to the topic. SH2 explores the issues of democratization of communication channels, and their impact on society. Studies devoted to the real environment, educational models, and transfer of skills are referred to as SH3. The content activities and construction related to the cultural studies and dissemination of past and existing tangible and intangible artifacts are referred to as SH5/SH6, up to local and geographical data management (SH7). Moreover, the PE6 sector is prevalent in the macro-sector PE, devoted to computational systems, guided and autonomous algorithmic methods, and user interface (HCI). It is emphasized that these connections and their different roles and weights within the methodology are strictly outlined in AR for architecture. This fragmentation (Figure 1) involves numerous studies, which mainly deepen acquisition, tracking, visualization, and interaction aspects, suggesting a technological and algorithmic solution [10; 11; 12; 13]. Only a few are devoted to explaining the whole workflow in the built realm [7; 14], or focused on transferring knowledge [15]. This lack may depend on the peculiarities and problem-solving approaches of the research in question, which can develop specific aspects without managing the subject as a whole. This specificity promotes the interest of experts in the domain, adopting a language and terminology consistent with the field, limiting the transdisciplinary dissemination of content, and promoting a watertight circuit that feeds itself. This review aims to address an overview of AR in the architecture domain, encouraging a transverse and transdisciplinary reading of the entire pipeline and its specificity. The article follows a holistic approach, collecting the different experiences conducted in the field with the purpose of:  
* Defining AR framed in the path of architectural knowledge;
* Organizing the AR pipeline, highlighting the main aspects of the chain;
* Outlining the state of the art of AR in the architecture domain;  
The in-depth study of these topics will be developed according to the following sections: Section 2 is dedicated to the definition of AR and its location within the reality-virtuality continuum, making some initial critical considerations. From Section 3 to Section 7 are discussed the main methodological steps. Specifically, in Section 3 are presented the main criteria to build an AR project, analyzing each inference with the architecture domain. Section 4 is devoted to digital content creation, explaining the levels of iconicity and data typology. Section 5 traces the primary HW and SW elements in an AR system, from the different devices to the tracking and registration systems, up to the HCI. Section 6 is dedicated to an in-depth analysis of the currently existing AR platforms related to the world of architecture, deepening the different types, purposes, and potentialities. Section 7 addresses the issue of feedback on the AR experience--a critical matter, especially in education, but necessary to improve the experience offered by AR. Finally, Section 8 is dedicated to the state of the art of AR research in Architecture, verifying the different topics related to the built domain. Some brief critical conclusions on the in-depth study close the review.