## 2 Research Methods
### Resources  
ACE education possesses domain characteristics under the special nature of engineering history and practice. Although AR has been applied in education, no systematic analysis has yet been performed. The development of an AR system can comprise computer science, medical science, and other fields in a collaborative manner of hardware and software system built-ups. To elucidate relevant trends and research issues, the selection of an appropriate database needs to be focused on this domain.  
The review starts from selecting a specific database, which has a close relation to ACE education. An analysis is conducted for all of the published studies in the database to the end of December 31, 2018, with the purpose to understand research trends, advantages, and challenges. Scopus seems to be relatively more focused and related to ACE, with the world's largest abstract and citation database of peer-reviewed literature, including scientific journals, covering research topics across all scientific and technical disciplines. The database also aims to provide references and recommendations of journal papers for scholars in the future to enhance teaching effects and learning quality.  
Journal papers were searched in the Scopus database and filtered through keywords in the paper title, abstract, or keywords list. The research questions were raised and transferred into coding schemes from basic information, systems, and challenges. Data analysis and discussion were also performed afterward. We selected 1299 papers based on certain keywords, including \"augmented reality\" and \"architecture\" or \"building\" or \"engineering\" or \"construction\", and \"education\" or \"learning\" or \"teaching.\" Non-journal and non-ACE education related papers were removed. A total of 21 papers (see Appendix A) were in the final analysis list (Figure 1).  
\begin{table}
\begin{tabular}{c c} \hline RQ1 & What are the extant trends? In which courses is AR used more frequently? \\ \hline RQ2 & What are the AR system development programs? \\ \hline RQ3 & What are the common learning strategies, pedagogies, and research methods? \\ \hline RQ4 & What are the advantages and challenges? \\ \hline \end{tabular}
\end{table}
Table 1: Research questions concerning applying augmented reality (AR) in architectural and civil engineering (ACE) education.  
Many AR-related researches contribute to ACE. The most important part of the review in the domain-specific field (i.e., ACE) is to ensure that high quality journal papers will be identified. A variety of combinations were employed to achieve this goal. In the early stage of search, very few journal papers were found in Scopus using both \"architecture\" and \"civil engineering\" as keywords. To avoid missing counts of papers, \"civil engineering\" was replaced by \"engineering\" with keywords \"construction\" and \"building\", and with an \"or\" search. Eventually, 21 papers were retrieved.  
Over-emphasis of domain-specific studies may lead cross-domain contributions to be ignored. Although AR studies in different fields are equally important and influential, domain-specific studies, which have been applied with clear and defined results, would contribute meaningfully to ACE. In this study, the majority of core topics or courses in the department of architecture and civil engineering are closely related, such as construction method, structure system and analysis, building materials, computer graphics, 3D modeling, etc. This is why certain keywords, such as \"urban\" and \"city\", were excluded, along with numerous other important ones.