## 7 Conclusions  
The benefits of AR in the AECO industry have been widely demonstrated in the literature. However, technical limitations about placement accuracy and model stability must be overcome. Our paper fills a gap in the current literature by proposing an assessment approach of main placement methods proposed in the literature in terms of accuracy and model stability. The factors influencing the placement of the 3D model in AR placement was examined by testing and comparing several solutions with or without markers. The results show that the range of placement errors by AR is highly variable (from a few centimeters to meters). It was demonstrated that the stability of marker-based AR is relatively lower, which is strongly influenced by the quality of the markers, the lighting conditions, the distance between the marker and the camera and the maturity of the SDKs. An analysis of the usability of the tested AR placement methods in AECO projects was proposed to guide the user in choosing the adequate method depending on the application requirements. In this context, the study focused on a 3D model for the study of the degree of placement of the different approaches. In a perspective, the results obtained and discussed will be a solid basis for the integration of our BIM-AR projects in the field of AECO. This research concentrated on a 3D model for the analysis of the placement of the various approaches. In a way, the findings and discussions will provide a strong foundation for the integration of our BIM-AR projects in the area of AECO. We can draw the following conclusion from the tests:  
* For a precise and exact placement in a real environment, the BIM-RA system faces challenges that must be overcome. The range of placement error by AR is highly variable, according to test results (from a few centimeters up to meters)
* Prior to use, each technique requires initialization (detection of planes, corners, points of interest, etc. ), GNSS planning (for techniques based on GNSS positioning, such as SiteVision), or the placement of physical marks on the site (for techniques based on markers). * Each method's actual use in the field has a significant impact on how precisely and accurately it places AR. * The cost (of the material, the license for the application, and the development), the use, which responds to various cases: precision work or simple visualization, and the time to develop a solution all play a role in the decision of a 3D model-RA placement method (use of an already ready solution or development of an application on a game engine). However, with all the methods and solutions used, our approach was limited to a single environment. As a future work, we recommend conducting further studies in this field to take into consideration other scenarios, such as underground network, work in progress, etc. Furthermore, future research is recommended to cover how to reduce errors and improve accuracy based on hybrid (sensors and vision) placement approaches [67] and how to perform qualitative assessment and quantity of the placement by smart glasses (example HoloLens 2). Additionally, as it has been stated by [12], the system 3D model -AR placement evaluation methods should be studied in different outdoor environments in order to study the effects of factors, such as clear areas, cluttered areas, etc., on the accurate placement of the 3D model. Additionally, having a larger sample of on-site measurement points would help support the findings of this research. Finally, by comparing the previous mentioned factors in the marker-based approach in order to study their effects and corresponding weights of influence, we suggest that future research be conducted on this issue. Conceptualization, N.E.B. and R.H.; Formal analysis, N.E.B. and Y.B.B. ; Investigation, Z.B. ; Methodology, N.E.B. and R.H.; Project administration, N.E.B. and R.H.; Resources, Y.B.B. ; Software, Z.B. ; Supervision, A.K. ; Validation, R.H. and A.K. ; Visualization, Z.B. ; Writing--review & editing, N.E.B.