## 4 Discussion
### Contributions and Limitations  
This study contributes to historical preservation efforts by presenting a constructive combination of AR analysis, GIS historical map management, video conferencing, and the secondary reconstruction of results. The advantages of this study include the fact that it can be used as a reference for composing AR models, confirming the relative scale of building components, communication between remote sites, and recursive 3D reconstruction.  
Our validation experiment also included an examination of whether the proposed system can be applied overseas. In addition to the Taipei area, the most remote site was in Okinawa (Figure 6g,h), Japan, where AR models were downloaded to compare how the local stone layout was different from a former brick construction in Taiwan. The setup  
Figure 11: Redefined transparency of AR model to highlight brick edge and layout.  
Figure 12: Cross-warehouse comparison for checking the alignment of the building corner finishes.  
included a Sony Xperia 1 \(\Pi^{\textcircled{B}}\), with CHT, Chunghwa Telecom Co., Ltd., Taipei City, Taiwan, which was the international roaming service provider. This smartphone could still facilitate AR interaction 600 km away from where it was originally tested.  
We found that the inserted AR model and the background can be reconstructed as a new 3D result. This approach required a novel modeling process to reconstruct the remote interaction result again in 3D after the interaction. As indicated in Figure 13, both sides of the remote parties can either take screenshots from different angles of the AR scene or record the conference video and retrieve frame-by-frame data for photogrammetric modeling.  
We found that a reconstructed result can be referred for a follow-up reconstruction process to verify building types, evolving stages, arrangements, and the levels of remodeling required to meet today's preservation needs. Cross-referencing back and forth between real and virtual models can be carried out to facilitate, for example, ground-level treatment. It appears that the brick details had evolved, having diversified forms and decorations in articulated building parts. As a result, remote manipulation can generate 3D models in either virtual or 3D-printed forms afterward. This is proof of the fact that the relative allocation of the AR model is related to the background. In addition to comparing the two sets of brick details, such models' application can be extended to virtual installation to confirm results. Moreover, secondary reconstructed results can be cloud-accessed on site to confirm former installation works.  
The proposed process is still evolving. The process was recreated recently using Line(r. 4.0.0) instead of Skype(r. 8.125.0.201). Although both are instant communication applications, the vast popularity of the former led us to apply AR to it for daily use. The first test led to results that were unsatisfactory compared to our experiments using Skype(r. The quality of field secondary reconstruction may suffer under unexpected lighting conditions, when there are internet band width issues, and in cases where video conferencing software is being used on a smartphone with a middle-grade CPU. In our test, video frame lags occurred. Hence, an alternative method involving the use of a screen recording app to reduce the dependence of continuous network connectivity was adopted.