Integration of BIM and Immersive Technologies for AEC: A Scientometric-SWOT Analysis and Critical Content Review

With the outset of Industrial Revolution 4.0 (IR 4.0), every sector is escalating to get enrichment out of it, whether they are researchor industry-oriented. The Architecture Engineering and Construction (AEC) industry lags a bit in adopting it because of its multi-faceted dependencies and unique nature of work. Despite this, a trend has been seen recently to hone the IR 4.0 multitudes in the AEC industry. The upsurge has been seen in the usage of Immersive Technologies (ImTs) as one of the disruptive techniques. This paper studies the literature based on ImTs, which are Virtual Reality (VR), Augmented Reality (AR), and Mixed Reality (MR) integrating with Building Information Modelling (BIM) in the AEC sector. A total number of 444 articles were selected from Scopus following the preferred reporting items for systematic reviews and meta-analysis (PRISMA) protocol of reviewing the literature. Among the selected database, 64 papers are identified as the result of following the protocol, and the articles are divided into eight domains relevant to the AEC industry, namely client/stakeholder, design exploration, design analysis, construction planning, construction monitoring, construction health/safety, facility/management, and education/training. This study adopts both a scientometric analysis for bibliometrics visualization and a critical review using Strength Weakness Opportunity Threat (SWOT) analysis for finding gaps and state of play. The novelty of this paper lies in the analysis techniques used in the literature to provide an insight into the literature, and it provides directions for the future with an emphasis on developing sustainable development goals (SDGs). In addition, research directions for the future growth on the adoption of ImTs are identified and presented based on categorization in immersive devices, graphical/nongraphical data and, responsive/integrative processes. In addition, five subcategories for each direction are listed, citing the limitations and future/needs. This study presents the roadmap for the successful adoption of ImTs for industry practitioners and stakeholders in the AEC industry for various domains. The paper shows that there are studies on ImTs with or without BIM; however, future studies should focus on the usage of ImTs in various sectors such as modular integrated construction (MiC) or emerging needs such as SDGs.


Introduction
For humans, a vital method of interaction with information is via reliance on communication through the spatial medium. The Architecture Engineering and Construction (AEC) industry is inherently related to the spatial environment and requires the provision of delivering information in multi-dimensional space to uplift the market [1]. With the advancement in computing technologies in the field of construction, we have witnessed myriad changes in the comprehensive approach to designing and constructing buildings.
One such amelioration is Building Information Modelling (BIM) which is defined as a digital illustration of tangible and operative properties of a built asset to facilitate decision making at each stage from inception to demolition [2]. The adoption level of BIM has significantly risen in the last decade around the world to about 73% adoption in the UK industry as per a National Building Specification (NBS) report 2020 [3]. Despite having several advantages, the communication flow in terms of interoperability between various stakeholders limits the adoption and implementation of BIM [4,5], as the walkability in a project on a real scale requires integration with other visualization techniques [6].
The development of Immersive Technologies (ImTs) in recent years provides the solution to this glitch by providing a platform for different stakeholders to get fully immersed during the various stages of the project [7]. ImTs imitate the real world or merge with it through a digital medium to deliver a sense of immersion in the simulated world [8]. Stimulating senses like visual, auditory, tactile, olfaction, and gustation are vital in achieving immersive experiences [9]. Virtual Reality (VR), Augmented Reality (AR), and Mixed Reality (MR) are the common ImTs that are prominent in the AEC industry for making the user experience more interactive and realistic [6]. Table 1 compares the features of VR/AR/MR in terms of real, virtual, interactive, and immersive levels experienced in each reality. The multiple options provided by integrating ImTs in each project's stage make them a suitable visualization medium for facilitating stakeholders involved at each step [10]. Currently, considerable studies are investigating how to leverage ImTs in the AEC industry. Li et al. [11] highlighted the usage of VR technology for construction workers to identify and assess risks in a construction project through training and experience, finding that VR was an effective strategy that is recommended for construction safety training. In a recent study, Muhammad et al. [12] applied VR for site layout planning and collision detection, showing its effective nature when compared to traditional methods. On the other hand, many BIM-AR investigation models [13][14][15][16], research prototypes, and research models also exist [17]. Finally, BIM-MR integration in recent times is quite astounding, ranging from conceptual to operational phases of a project. Naticchia et al. [18] merged information from a BIM model with an MR environment to reflect the maintenance workers' benefits. Another fieldwork facilitated through MR was done by Ammari and Hammad [19], who proposed a framework to collaborate BIM and MR for supporting field tasks in the facility management domain. Most recently, S. Sepasgozar [20] used MR technologies as a digital method for AEC pedagogy in the construction courses for the universities. He presented a combination of five digital technologies using MR techniques and digital twin to add value to the literature by describing the construction courses' effectiveness. Talking about the civil engineering aspects, Protchenko et al. [21] used VR/AR solution to enhance the usefulness of the structural system, and Orihuela et al. [22] proposed the application of the Lean philosophy with the use of immersive applications during the life cycle of a project at different steps. Many universities have increased their research programs focused on ImTs applications in recent years to explore the enormous amount of prominent ways to automate the AEC industry, especially after the outset of Industrial Revolution 4.0 (IR 4.0) [23]. From conceptual and theoretical frameworks to lab evaluated prototypes to field-based knowledge applied results, ImTs has transformed the nature of work in the AEC industry [24] and will continue to do so in the future.
The amalgamation of BIM with these ImTs is not only leveraging the smart and convenient way to be adopted in the AEC industry, rather they have a considerable impact on many other facets, namely the business promotion of projects, research studies in institutions, and enhancing the education of AEC professionals. As a matter of fact, International Data Corporation (IDC) reports the upsurge in ImTs wearables will escalate from 4.2 million numbers in the year 2018 to 53.1 million numbers by the year 2022, which accounts for the significant growth of 88%, also called the compound annual growth rate (CAGR) [25]. Overall, ImTs are providing the solution to the glitch which the construction industry was facing and will be the new dependency tool in Construction 4.0 (C-4.0). Based on the model of IR 4.0, C-4.0 is an amalgamation of construction industry digitalization and construction processes industrialization [26]. Although IR 4.0 is a broad term with no specific definition; its aim is to leapfrog the integration of modern trends and cuttingedge technologies to enhance the way of making things [27]. C-4.0 can be defined as connecting the latest technologies to decentralize the connection of a user to physical space ubiquitously to achieve real-time decision making of a project often called Digital Twin (DT) [28][29][30]. The development of C-4.0 is still a buzzword, but it will surely gain momentum among researchers and industry professionals, especially after the prevalent COVID-19 pandemic. A recent study by Pavon et al. [31] though utilized BIM possibilities to reduce crowding and facilitate social distancing as a COVID-19 measure in a public building, but in the future more studies will utilize ImTs with BIM to facilitate AEC works.
Although ImTs have great potential to be used for the AEC industry, they are still below par, as ImTs lack robustness [32], especially to be used in tough conditions, usually at construction sites, and thus reliability towards their usage becomes a challenge in the construction sector [33]. The complex and different occurring factors in the AEC sector limit the implementation of digital technologies. Moreover, the construction industry lies very low in adopting new technologies [34]. Although the significance of ImTs is still not completely capitalized on in the AEC industry, it has gain momentum in some other industries already. One such industry is gaming and entertainment, which has provided human consciousness, stimulates human senses, and gives locomotion abilities to players [35]. In the past decade, several literature reviews have been done to show the state of the art of ImTs in the AEC industry. Despite the useful identification of ImTs' research areas, the respective discussions in earlier studies are more focused on the scope of a few domain studies which come under the industry. Additionally, existing review studies have a narrow perspective, focusing on a few domains or on specific applications. As a fact, Zhang et al. [7] reviewed the state of the art of VR applications, giving insights into the benefits and challenges. Cheng et al. [36] reviewed 87 journal papers on MR applications, classifying them into architecture and engineering, construction, operation, and multiple stages. In addition, Diao and Shih [37] reviewed literature from the Scopus search engine to address AR capabilities in the education domain to discover its wide range of advantages and challenges. In fact, a study offering a whole picture of the subject domain in the AEC is still missing. The complex nature of the AEC industry needs an up-to-date, inclusive picture of ImTs through visualizing and understanding trends and patterns to find relevant research themes, keywords, and their link to each other.
As an attempt to fill this considerable gap, this review stands out among the other previous reviews made in this domain to comprehensively present the overall landscape and core perspective of the knowledge body about ImTs in the AEC industry using the Strength Weakness Opportunity Threat (SWOT) analysis method. This study contributes to the sphere of knowledge in the field of ImTs in the AEC industry by identifying the scope and limitations prevailing, assessing the standard of the current and existing body of knowledge. Additionally, presenting cutting-edge technology, highlighting inadvertencies and paucities, and determining the possible future research prospects efforts. The objectives will be to identify and define the current mainstream research topics within this field by finding domains in the industry and SWOT analysis to propose the research directions. Theoretically and practically, the review study will present a valuable point of reference for escalating the knowledge of various stakeholders present in the AEC industry in planning the future agenda concerning the adoption of ImTs in their respective area, along with the implications for both the academics and practitioners to understand as well as find the glitch.
The next section in this study, Section 2, describes the key definitions and concepts, highlighting the overview of ImTs integrated with BIM, summarizing the different definitions and applications related to the AEC industry to understand various terms, perspectives, multiple disciplines, and the theory involved. Section 3 will present the research methodology applied in this study for the systematic literature review. Section 4 analyzes the retrieved papers from Section 3 based on scientometric analysis to reflect the keywords, themes, contributing institutions, and countries in the literature. In Section 5, a SWOT analysis based on content analysis of selected articles is performed along with the limitations of this study. Further, limitations/future needs for the literature are presented in Section 6, finishing with ensuing conclusions in Section 7. A fusion of existing literature and studies in a subject field can elude the recurrence, duplication, and reappearance of like research and studies and will lead to unleashing relevant voids and gaps which are necessary not to be overlooked and unnoticed [38].

An Overview of BIM and ImT's
The knowledge development of a research field is a continuous process, and it is often or most likely motivated through earlier enhancements in it. A joint systematic examination of various knowledge areas will increase the development of BIM amalgamated ImTs by illustrating and knowing the information achieved till now. BIM, as a process, is one such knowledge development in recent years that can store, produce, deal, arrange, substitute, and exchange data from one party to another. The significant part of BIM is it's (I), which is information. Therefore, it can also be summarized by saying Modelling the Information to achieve a Building. BIM uses a methodology to create, share, exchange, and manage the data [39,40]. However, apart from having multiple benefits, its usefulness has not achieved the full credit it should get. Again, the reason for such discrepancy is the flow of information, which is difficult to perceive on a real scale and ultimately reflects the plausible feebleness of BIM. In this regard, the application of ImT's in the AEC industry is a remarkable breakthrough that will stay for a long time as a computing platform for AEC professionals to build innovative ways of learning, connecting with others, and working to eliminate the real world with the virtual world. Li et al. [41] investigated the state-of-the-art application of ImTs in the safety processes in construction. The rapid evolution and advancements in mobile and computer technologies have made it possible for professionals to keep various aspects of their projects in an easy way. ImTs provide the seamless communication of the data, which makes the end-users always and everywhere connected with the virtual environment to get the knowledge of their facility. The synergy of BIM and ImTs paves the way to endless opportunities and possibilities [42]. VR, AR, and MR collectively diminish and blur the opacity between a real and digitally active world with the inclusion of immersion using mobiles, tablets, and other gadgets. This makes the experience more realistic, and will keep on escalating the quality of end products in the AEC industry to a new level.
These immersive realities come under an umbrella name, Extended Reality (XR), which can be termed as a superset, including reality to virtuality as a complete spectrum which is first presented as a concept of reality virtuality continuum [43]. The implication of XR lies through the range of user perspective to senses as VR to cognitive acquisition as AR until complete human-computer communication as MR; the association continues and evolves. Therefore, XR refers to various real-virtual-human computer interactions via Information and Communication Technology (ICT) techniques and wearables techniques. Additionally, X in XR, which is an extended theory, relates to any future spatial recognition within new technologies to come. Immersion can be summarized into four subsets, namely spatial immersion (virtual effect spatial arrangement), emotional immersion (emotional absorption of a user through content description), cognitive immersion (brain encountering the best result), and sensory motoric immersion (through the recurrence of feedback from senses and actions) [44]. Figure 1 shows the major types of ImTs and immersion levels associated with them. All these technologies have their own share in escalating the AEC sector with VR, which is sometimes called mental teleportation in helping to improve collaboration, facilitate decision making, design communication, better perception, credibility raise of the design, decrease costs, and save time. On the other hand, AR eases design checking, deviation analysis, spatial layout planning, step by step inspection on-site, and logistics. MR also called AR 2.0, makes visualization in 3D reality, facilitates seamless translation, increases helps workflow integration, and improves communication and collaboration among various stakeholders [38]. Following this background, this section will outline the amalgamation of BIM with VR, AR, and MR as ImTs in the AEC industry.

BIM with VR
The quest of involving clients who have limited or incomplete knowledge of a project is increasing in the AEC industry to give them a better understanding of the outcome [45]. The ability to interact with BIM models can be easily filled by VR, which is a digital mimicry experienced by the user to visualize virtual content by immersing a person in a virtual domain environment to interact with 3D models generated by a computer [46][47][48]. VR can be achieved by preparing 3D modelling of a project and then generating its virtual reality environment. Most likely used software platforms for 3D modelling stages are Autodesk Revit, Archi CAD, All Plan, Vector Works, Rhinoceros, Sketch-Up, and 3-Ds Max. For preparing virtual environments, software platforms such as Unity 3D, Unreal Engine, and Torque are the most common, among many others [22]. The sense of inclusiveness also makes clients invest more, and they can use this information in their marketing strategies as well [49]. In addition, as construction is a high-risk industry that has a high rate of fatal accidents around the globe, VR can ease the work to estimate the risk and potentially prevent it. The five human senses-vision, hearing, touch, proprioception, and smell can be mimicked by VR through human-computer interactions, and it can also have controlled the generations of signals that six-dimensions (three translational and three rotational) of a human can experience [50].
The literature shows that virtual reality provides a high level of information in an immersive environment, which can be used for training and safety purposes. For example, visualization of underground areas and activities as high-risk spaces for construction can be turned into an immersive environment, and this provides useful information to freshly graduated students and novice practitioners. Figure 2 shows details of a tunnel boring machine, and the user of this immersive environment as an avatar can communicate with other avatars and share their experience and knowledge at the same time. This practice can be applied to other construction activities and can be known as one of the strengths of virtual reality for representing high-risk activities in construction. Along with having a plethora of advantages, the sensitive, cognitive, and perceptual points are sometimes missed in VR [51] due to insufficient sensory feedback, which gave way to AR, and thus MR. The quest for more refined hardware and software used as a technology driver to experience immersive, holistic, tangible, realistic, touchable, and perceptible VR solutions is a search for technology developers around the world to provide a seamless experience to clients [41]. Overall, VR integration with BIM will bring numerous bright advantages in the AEC industry for construction officials, will enhance the collaboration process, and provide a communication platform for real-time interactions [52,53].

BIM with AR
The vast amount of information that a BIM model holds within it is difficult to structure and exchange, which can affect efficiency at a construction site in addition to a huge amount of time for site workers [54,55]. However, AR is an effective way of retrieving the information and providing a seamless medium to project the information [56,57].
The history of AR is 30 years back when the term is coined by Boeing researcher Tom Caudell in 1990 [58]. However, Azuma's (1997) definition of AR is widely renowned and accepted among researchers, which states AR to be the superimposition of the virtual world over the real world to enhance reality perception [59]. There are many other definitions of AR stating its benefits in the AEC industry by various researchers; some of the definitions are given by [41,60,61] to reflect the added usefulness of the AR environment with BIM. AR is different from VR in augmenting the space with real and virtual information to existing at the same time, where a user can interact intuitively, unlike replacing the real content, which is a drawback of VR [62]. Rather than providing a synthetic reality, AR overlays more information onto reality [63]. AR for AEC dates to the year 1996 [64]. The vast amount of data and interaction involved in the construction project can be accessed easily by AR, thus making it an important and seamless possible way for detecting aspects involved with the view of a user.
Limitations of AR can be technological, user interface centered, and social acceptance by end-users. An AR system is mostly hindered by a lack of effective sensors and trackers with long-range [62]. Although AR is the most effective way to encourage the 3D outputs to date and systems have become advanced in recent years, the sense of nausea, claustrophobia, and motion sickness still occurs on a certain scale, which should be the concern for the researchers and industry persons in the future. The significant drawback of AR is that the user can't interact or manipulate the augmented objects, rather they only add the information. This concern is rectified in the MR environment, which is an extension of AR. Lastly, Microsoft, Google, and Apple are among some tech tycoons who have invested a lot in AR in recent years and propend it to be the next revolution, speculating that the wide reach of AR would be the end of mobile phones.

BIM with MR
As the name suggests, MR contains the mix of real and virtual world controlling the multiple tasks involved in a facility. MR is a combination of augmented reality (AR) and augmented virtuality (AV) blending to form and produce new visualizations and environments [65]. MR displays the spectrum of reality involving the environment generated through computer-based intervention [66,67], which makes it a potential candidate for the AEC industry, as it requires various levels of relations among stakeholders [68]. VR and AR have a level of obstruction and obstacles, which could not provide an extreme level of interaction; however, BIM-integrated MR being the more flexible environment provides hindrance-free collaboration, which makes it more useful as a marketing tool for developers. The freedom of interacting with the objects and manipulating them simultaneously like in the real world makes MR different from AR and more effective for the AEC industry. The MR systems follow holographic technology, which presents holograms for various digital assets that can be navigated and controlled by gestures, gaze, and voice commands. Although MR and AR are similar in many ways, the application areas of MR are different than AR, as it provides a more realistic, accurate, and immersive form of AR [69]. Table 2 compares some factors to consider when choosing between MR and AR as good, average, and bad. Interaction of user with MR, movement of body parts, cognitive and perceptual tasks are some of the ergonomic features which need to be taken care of [70]. On the flip side, the rapid and adaptable growth of MR devices possessing user comfort frequently has the capacity to make the industry compulsive in using them.
As the AEC industry is accident-prone, the incorrect interpretation of information is common, mainly due to a less skilled workforce, which eventually increases the cost of a project, reduces the quality, and delays the schedule. Although the adoption costs of MR techniques are higher ultimately, the firms who will adopt this change will go out to win in the end. Overall, on a rudimentary level, MR will be embraced by the firms in the future at a vast level, as the onset of Construction 4.0 [23,71] will digitalize the industry, providing a paradigm shift in the working culture of AEC firms. The summary of definitions and applications of ImT's is presented in Table 3.

Articles Retrieval
To organize the literature for the review process, the PRISMA method is used [161]. It is a systematic collection method of data following the four-step process of identification, screening, eligibility, and inclusion of the records. Similar studies have adopted this approach for the review process and content analysis [162,163]. Figure 3 explains the collection process through the PRISMA approach. Identification-In this phase, the relevant records were recognized by including only peer-reviewed journal publications and conference proceedings. Conference papers are a convenient method to better understand what is ongoing in a field with up-to-date knowledge [164]. An unconstrained and unconstructed search was done initially for finding the relevant publications in the field of amalgamation of BIM and ImT's in the AEC industry. The relevant keywords were extracted based on publications investigation and authors' experience, following by a literature search, a two-way process, namely database search and supplementary search [165]. The keywords found during an unconstructed search assist in database searching, and a supplementary search was done based on publications from unconstrained and database search.
The keywords for this study were breakdown into BIM, Immersive Techniques, VR, AR, and finally MR for the AEC industry. After getting keywords from unconstrained and unconstructed searches, Scopus, which is considered as one of the authoritative database engines for academic data, was used. As compared to the Web of Science, Scopus has a wide variety of journals and publications [166]. Most articles in Web of Science are also included in Scopus. The data structure in Scopus includes literature types, authors, journals, keywords, abstracts, institutes, and references. Additionally, the Scopus API search gets shared results by using the Boolean syntax system. Keywords were input in Scopus search engine using the TITLE-ABS-KEY as follows: (BIM OR "Building Information Modelling*") AND TITLE-ABS-KEY ("virtual* reality" OR "augmented reality" OR "mixed reality" OR "immersive* technologies*"). Here "*" denotes a fuzzy type of search which includes words like model or modelling.
A total number of 608 articles (journal publications and conference proceedings) were found at this step of the search, and 104 articles were found from supplementary searching from famous journals of the field, as the concept of BIM and ImTs is significantly broad. Finally, 712 papers were retrieved from an unconstructed and unconstrained search. The process of unconstructed and unconstrained search is shown in Figure 4.
Screening-The filtering process in the screening stage of the search was then carried out in the following ways: 1. The limitation of the year was applied, and papers before 2010 were not considered as the relevant focus of this review study was towards the latest publications since the last decade. 2. Subject area was limited to engineering, computer science, social sciences, environmental science, energy, and decision making. Fields like medicine and business were not relevant to the study and were not considered. 3. Document and source type was restricted to conference and journal articles. 4. Papers not in English were removed, as they could not be reviewed in this study. Additionally, 78 papers were removed as they were repeating and duplicate in nature. 444 articles remained after this step for the eligibility phase.
Eligibility-The articles judged at this stage were 444 in number after the proper screening at an earlier stage. The filtering process in the eligibility stage of the search was then carried out in the following ways to remove the papers which: 1. Lack of focus on BIM integrated ImT's; 2. Were related to other fields like manufacturing; 3. Were not a direct application of VR, AR, and MR in the AEC industry and the concept of VR, AR and MR appeared just as a general term without having much stress towards the construction industry, resulting in an uncertain relation to the subject matter. Therefore, after passing the eligibility test, 64 articles remained for inclusion in the study to be further analyzed.
Inclusion-A total number of 64 articles remained for qualitative SWOT analysis in this stage to develop a fundamental understanding of their contribution towards BIM integrated ImTs in the AEC industry. The studies included applied multiple approaches to address their aims, including pilot study, case study, survey, and questionnaire, among others.

Bibliography Analysis
The 444 articles from the eligibility phase of the PRISMA protocol went through the bibliography analysis of the BIM integrated immersive technologies data set. The analysis identifies the keywords, themes of the dataset, contribution of countries, and major institutions in the current literature. Vos-Viewer [167] is the science mapping tool that was used to analyze the results, which is shown in Section 4 below.

Content Analysis
The rigorous review and study of the papers to form themes or domains is an effective way to monitor and structure the data for useful results [168]. The content analysis of all 64 papers was conducted for better synthesizing the qualitative data, and eventually, papers were divided into eight domains concerning the AEC sector, including client/stakeholder, design exploration, design analysis, construction planning, construction monitoring, construction health/safety, facility/management, and education/training. The results are discussed in Section 5. The domains are obtained as a result of themes generated in the scientometric analysis.

Scientometric Analysis
The scientometric analysis is used for mapping the scientific retrieved data [169] for evaluation of themes, dynamic aspects of data, and processing a wide range of information [170,171]. Furthermore, it gives impact measurement of journals and articles, institutes, countries, subjects, and keywords, which delivers the indicators for policy management across the subject removing subjectivity issues among the pieces of literature [172]. VOS-Viewer [167], Cite Space, the science of science tool, Bib Excel, and Gephi [173] are some of the common software's used to present scientometric analysis. The scientometric analysis is also used in review-based research for similar kinds of AEC topics, such as construction engineering and management [174], computer vision applications in construction [175], artificial intelligence in the construction industry [176], global BIM research [177], and interoperability issues in BIM [178]. Figure 5 provides an insight into the selected data from the eligibility phase of the PRISMA protocol showing the important keywords in the literature. The color of keywords denotes their likeness and interconnections, while a circle's size denotes its weight [176]. The larger the circle of an item, the higher the weight in the network. The distance attribute says the relatedness among the keywords, which is in terms of co-occurrence linkage. Therefore, if two keywords are close, the connection between them is stronger. Keywords usually have clusters associated with them, which shows the close interdependencies and relatedness among them [174]. Keywords co-occurrence provides the mental map of research topics in the field and facilitates the researchers to identify the relation between those keywords. Moreover, this mapping helps to identify the clusters and frequency of keywords addressed, which paves the way to fill in the gaps for future studies [179]. The information provided by the mapping is free of subjectivity and gives the freedom to not read the whole paper. Through the screening of titles, abstracts, and keywords of the papers, VOS-Viewer generated the co-occurrence of keywords. Figure 5 reflects the significant keywords and their relative clusters in the BIM integrated ImTs study. After setting the frequency of keywords to 20, 32 keywords are generated in the map. Additionally, there are no standard rules to set the frequency of the keywords' occurrence [180]. Further, the individual maps of four important keywords related to this study (BIM, VR, AR, and MR) are also displayed in Figure 6a-d. Moreover, the statistical description of keywords is shown in Table 4, including the occurrence and total link strength (TLS) of each keyword. The TLS reflects the number of links of a keyword with the other respective keywords. The analysis of the keywords occurred in Figure 5, and Figure 6 can lead to the following findings and discussions: BIM, being the central core of the study, has the highest number of occurrences and TLS value, as shown in Table 4. Figure 6a shows the strong links of BIM with VR, AR, and architectural design, reflecting the significant importance of BIM knowledge to achieve and perform immersive studies. Other than this, BIM has strong links with small clusters like construction management, design, visualization, information theory, and information management. However, the process of MR is still in its nascent stage across the AEC industry, which is clearly visible with its link to the BIM process. The evolution of BIM is significant in the industry, and with the likes of integration with simulations, IoT and Artificial Intelligence processes, it is leading to the Digital Twin process [180].   Figure 6b shows the connections of VR with other keywords. The link with visualization, architectural design, information theory, and 3D computer graphics is strong. This reflects that VR is mainly used as a visualization enhancing tool by the clients and other stakeholders of the industry. However, it also links with the mini clusters of construction management, facilities management, and design process. However, the low connection strength of VR with other mini clusters other than visualization is due to low sensitivity, and cognitive and perceptual points delivered by the VR process. This causes low adoption in the industry works, especially requiring accuracy and precision. This requires developers and technology drivers to develop more refined hardware and software solutions providing experiences in a more immersive, holistic, tangible, realistic, touchable, and perceptible way [181].
In comparison to VR, AR has low occurrence and TLS values but has strong connections with the facilities management cluster. The integration of an AR environment in BIM can facilitate the data in a more meaningful way, thus changing the outcome from a static nature to more real-time visualization, and hence providing seamless site management. The vast amount of data and interaction involved in the construction project can be accessed easily by AR, thus making it an important and seamless way of detecting aspects involved with the view of a user. This can be viewed in Figure 6c where AR has strong links between the construction management cluster and the decision-making cluster. Although AR is the most effective way to encourage the 3D outputs to date and systems, which have become advanced in recent years, the sense of nausea, claustrophobia, and motion sickness still occurs on a certain scale which should be a concern for the researchers and industry persons in the future [10].
Finally, MR has the lowest occurrence and TLS values among the three ImTs as seen in Figure 6d, and has links with only the facility management side of the AEC industry. This lack of studies is due to the newest nature of this immersive technique, which still needs the latest solutions to make it leapfrog in the AEC industry [182]. Corresponding techniques like better localization, improved display, integrated interaction, increased data storage, and collaboration can escalate the maturity of MR applications in the AEC industry [36]. Solutions like cloud computing, 5G technology, and AI techniques will increase the usage of MR applications in large-scale construction projects [36]. On a rudimentary level, MR will be embraced by the firms in the future at a vast level as the onset of Construction 4.0 will digitalize the industry, supplying a paradigm shift in the working culture of AEC firms. Additionally, the future way will be a Hybrid Reality, allowing the merging of all the realities into one joint system and allowing a person to switch back and forth into the real or virtual world depending upon the usage [182].

An Overview of the Application of Immersive Technologies in the AEC Industry
Mainly used for business areas, a SWOT analysis helps to frame the factors that can affect any company's market value, while giving future predictions too. However, it has been used for other industries as well, like career planning, urban renewal projects, web design areas, and academic research centers [183], among others. Additionally, it is best suitable to find the internal strengths and weaknesses of a certain unit along with citing the trends (opportunities and threats) which can be faced in the future. Figure 7 shows the pictorial representation of domains obtained as a result of themes generated in the scientometric analysis. Each domain reflects the use of ImTs linked to themes. The research domains obtained are structured based on existing research to facilitate the understanding of ImTs to give an overall picture of the subject matter and further state recommendations and future directions based upon the rationale. Table 5 provides the share of 64 articles for each domain and the percentage contribution from the articles analyzed for this study with reference for each paper.  It is evident from Table 5 that the design exploration domain and design analysis domain share an equal percentage, which clearly shows that the majority of ImTs in the AEC industry are applied in the design phase of a project. ImTs can prove to be an asset in the initial phases of the design for viewing the feasibility of different design options by allowing different stakeholders to visualize them [99,222]. It gives a clear picture of the pros and cons of the designed space by viewing it from ImTs, which also helps in exploring different options and analyzing the outcome for the smooth working of the project.
On the other hand, the health and safety of the construction workers at the site have always been an issue worldwide [223]. The damage caused by improper health and safety measures is irrevocable and sometimes leads to fatal accidents. In this regard, ImTs help in finding the potential threats which can occur at the site prior to their actually happening, thus reducing the chances for any issues to a large extent [209]. Therefore, the percentage of research about construction health and safety domain contributes largely to the research and will continue to depend on ImTs to create the simulated environment for the better judgment of health and safety issues at the site.
However, the percentage share of client/stakeholder domain, construction planning domain, and construction monitoring domain is comparatively low with respect to other domains, which shows that research needs to increase in these areas. The different nature of the client makes it difficult to make him/her understand the clear picture of the project due to technical factors involved in a project [224]. Additionally, options presented by the design team make it unclear for a client to judge a better outcome for his facility. However, with the growth of ImTs and the amount of interaction they can provide, it has become a trouble-free task for a client to understand the technical know-how of the project, which results in better satisfaction and outcome of the project [225]. On the other hand, the reason for a low contribution of the construction planning domain and construction monitoring domain may be due to many reasons. As the construction site involves many workers working at different tasks simultaneously, it is, therefore difficult to provide each team with access to immersive techniques due to capital issues [104]. Moreover, planning and observation of a construction task involve many miniature details where the approach of a worker becomes difficult, thus hindering the use of ImTs at that situation and place. However, in recent times, the integration of ImT's with technologies like drones has made access to remote locations at a site workable, and research in this direction will increase in the future [226].
Talking about the facility and management domain, the research in this direction is growing as ImTs deliver useful information for the workers to run and uphold the various facilities at a site remotely as well as in-person [213,215]. Supporting building maintenance work, repair, inspection, providing technical information to workers, and assisting in assembly/disassembly tasks are features provided by ImTs [213]. Lastly, a huge amount of research is inclined towards the education and training domain as the ImTs can deliver realistic scenes and scenarios for the workers to develop and gain the required skills and information needed at a site [227]. Moreover, the cost of training and educating the workers can be reduced with the help of ImTs by simulating the environment likely to occur at a site, thus reducing chances of potential threats, and resulting in health and safety issues.
Based on the contribution analysis of ImTs for various domains, the word cloud for the three most researched domains is presented in Figure 8, which reflects the most repeated keywords for the data set and gives the overall ideas and focus for the future. For example, words like safety, hazard, and workers, along with training and virtual, are relevant for the health/safety domain. They are the most researched terms and themes in the context of safety in construction [209]. Similarly, words like education, students, training, and learning, along with virtual and reality, frequently occurred in the education/training domain as the understanding of the tasks in a virtual environment is preferred for both construction students and professionals [95,227]. Finally, the keywords that occurred the most in the facility/management domain are maintenance, management, assembly, facility, and information, as these words form the basis of the facility management (FM) process through the integration of ImTs.  Tables 6-9), highlighting ImTs integration with them to give a clear picture of each domain. It provides the roadmap for future researchers and industry people to better strategize the adoption plans of ImTs for their respective interests. Finally, based on different analyses and research backgrounds, key emerging trends have been highlighted and discussed for future research, and development efforts needed to be focused on ImTs with BIM. The integration of BIM and ImTs at different phases of the project can improve productivity, saving costs and time, along with improving safety and quality.

RD-1 Client/Stakeholder RD-2 Design Exploration RD-3 Design Analysis RD-4 Construction Planning
·Agile gadgets ·Real scale built asset ·Wireless technologies ·Affordability in price ·Scalability and flexibility ·Advances in techniques ·Productivity enhancement ·Organisation reputation ·Spatial comprehension ·Devices comfortability ·Return on investment ·Escalation in business ·Visual realism ·Knowledge sharing ·Software knowledge ·Common data formats ·Resolve interoperability ·Integration with gaming ·Content creation skills ·Data trust with each other ·Data transfer classification ·Enhanced virtual meetings ·Cloud based management ·Avatars communications ·Synchronisation of data ·Proof of concepts ·Haptic control boost ·Olfactory simulations ·Sustainable experiences ·Sense and feeling of space ·Visual cues enhancements ·Advance user experience ·Standardised approaches ·Microclimate experience ·File size enhancements ·Better headsets for use ·Situational awareness ·Schedule prediction ·Utilisation of resources ·Non graphical data skill ·Enhanced collaboration ·Adding cyber physical order ·Adding RFID and GIS system ·Constructability analysis ·Cloud based interactions ·Complete set up package ·Utilising 5G technology ·Mixing computer vision ·Better delivery of asset  ·Striking graphics concern ·Difficult with hardhats ·Headsets strains ·High cost hindrance ·Technology change barrier ·Social interface discord ·Lack of many educators ·Uncertainty and disbelief ·Time required is high ·Fragmented content ·Stress on students

Limitations of the Study
The limitation of this research study is the amount of sample collected for this study. The search engine Scopus was the only source taken for the sample, not considering other search engines present in the research domain like Google Scholar and Web of Science. Scopus is the largest database of peer-reviewed literature. The data collected in this study is sufficient to encompass the main body of knowledge in this field. However, future studies related to this topic may include other sources and databases to have more consolidated information to achieve more comprehensive results.

Recommended Research Directions
Based on the content analysis and SWOT analysis of research domains for the AEC industry using ImTs, future directions are summarized in Table 10 below. Three broad categories were found with five subcategories, each to lay focus upon for the future work required in ImTs and BIM integration for the AEC sector. The directions are in the context of requirements of ImTs devices in the future, how the graphical/non-graphical data need to enhance, and finally, the responsive/integrative prospects. The distribution of each category further into five subcategories will pave the way for researchers and industry professionals to upskill those areas to extract superfluous rewards. when fully charged is a concern. 5. Heavy use can drain the battery quicker as construction sites mostly involve a long man and task hours. 6. Unreliable for long site works requiring consistency in the tasks.
1. Trackers used in the devices are not robust enough to track tricky geometry present. 2. Accuracy of devices is not up to mark. 3. Underground areas need accuracy to avoid any risk, ex: piping installation mechanism which often lacks in devices used across. 4. Plane geometry difficult to track as they lack detail aspect of tracking points. 5. Unreliable in risky areas due to the presence of unwanted objects and items. 6. Level of uncertainty is unavoidable in most cases as the process requires more robust tactics and strategies for the users.
1. Limited ability for model storage is a concern in XR devices at present. 2. Difficulty in storing complex BIM models due to large dataset in them. 3. Processing capacity is usually low, truncated and time taking usually. 4. True depiction of BIM models becomes as arduous task as the visualization process becomes broken due to presence of large number of objects and images involved.

Presence of huge metadata related
to objects is a cause of problem.   Lumion, Twinmotion and IrisVR can leverage this problem to some extent but a holistic approach in this direction is still need to be researched and focussed.
1. Need development for XR devices and environment which can provide various predictive states for the AEC project such as time, cost, hazards, safety issues, loads etc. 2. Big data and AI features will be required to enhance the current XR devices to have a predictive and prescriptive analysis of such kinds. 3. Also, the processing power needs to be escalated for providing simulations and optimisations for better decision making of a project.
1. Teleoperation processes as related to physical operation are notably safer in the AEC industry, which has hazardous, risky, and detrimental environments around many tasks faced by a worker. 2. The future potential of teleoperation in the AEC sector will rely upon better sensory integrations and a combination of human & robotic capabilities to enhance the physical and virtual worlds. 3. The risk and safety factors for most of the used cases will be minimised.
1. Need for integrating different sensory inputs to deliver intuitive communication between objects and users in AEC tasks. 2. Addition of senses in the XR experience will lower the cognitive load of a user along with providing safety in the tasks. 3. Various AEC tasks involving health and safety issues can be minimised through the integration of many senses; they will provide a natural environment and the future requires proper engagement.
1. Enhanced decision-making for the site operations with the inclusion of IoT sensors data with XR devices. 2. Automated site monitoring along with materials and equipment checking will get facilitated. 3. Accuracy in the assessment of task including risk factor as the information received will be updated and revised. 4. Development needs to be directed towards finding new data outlines, schemes, technologies, and methods for seamless integration.

Conclusions
This review presented a study on the integration level of ImTs with BIM in the AEC industry. The ImTs, which include VR, AR, and MR, have shown colossal benefits in the way AEC projects are designed, constructed, and managed. This review leveraged different analysis methods to present the literature landscape in the field of ImTs relevant for academicians and industry professionals. The outcomes of this review are 1. defining the literature of ImTs for different AEC domains, 2. doing a SWOT analysis of ImTs in each domain defined, and 3. highlighting current limitations and proposing future needs for successful adoption and implementation of ImTs. The research included the PRISMA protocol for collecting 64 articles for a critical review out of 444 articles from the Scopus search engine related to BIM and ImTs. The content analysis of all 64 papers was done for better synthesizing the qualitative data, and eventually, papers were divided into eight domains, which are governed in the AEC sector. The domains are client/stakeholder, design exploration, design analysis, construction planning, construction monitoring, construction health/safety, facility/management, and education/training.
A SWOT analysis of each domain has been performed to present the discrepancies and to give a clear picture of each domain. The overall adoption and implementation of ImTs have been found low, with few domains using it to a large extent compared to others. It was found that the design review and design analysis domain have been the most used cases. ImTs offers a support system for design decisions and the provision of analyzing the design outcome before the construction process starts. For construction planning and monitoring domains, opportunities to view and predict a complete forecast of the construction schedule is facilitated through ImTs. Moreover, ImTs deliver the utilization of resources over a due course of time and the need to deliver more contextual procedures for information to workers. The other domains like health/safety, facility/management, and education/training are also reaping the benefits through ImTs. It enhances better communication at a site between workers and construction managers. Additionally, workers leapfrog their ability to track learning progress based on the interactivity with the tools and techniques in respect to physical training.
Finally, research directions for future growth on the adoption and implementation of ImTs are presented. The directions are based on proposing three categories, namely immersive devices, graphical/non-graphical data, and responsive/integrative processes, along with subcategories for each category. In terms of technological advancement, bandwidth from fifth-generation (5G) technology will increase the efficiency of ImTs to offer remote collaborations better. The cloud-based ImTs driven by 5G network and edge cloud technologies will enhance the process of application development. It will escalate a clear understanding of the information between the physical and cyber worlds. Better user interface and interaction along with real-time training at a site to increase awareness will become the new normal. Real-time perceptive responses based on feedback will be strengthened because of better cloud computing and networking quality. BIM integration with cloud ImTs will increase the explicitness of task interdependencies, as the virtual and physical data will be shared seamlessly. The integration of BIM and ImTs will deliver novel workflows and escalates the AEC industry as technology-driven.
The significant contribution of this review is that it grouped the literature on ImTs in AEC domains for better understanding the factors limiting and driving in each domain. However, the applications of immersive technologies along with BIM can be explored further in different sectors such as modern methods of construction, specific volumetric or panelized modular construction, or 3D printing for achieving sustainable development goals (SDGs). In line with SDGs, the authors will continue this study to explore applications of mixed reality along with BIM for risk identification in construction.
Funding: This research received no external funding.

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

Data Availability Statement:
The data presented in this study is available on request from the corresponding author.

Conflicts of Interest:
The authors declare no conflict of interest.