## 4 Experiments and Results
### The Forum of Nora  
The roman forum of Nora constitutes the case study of a doctoral project in progress at the Cultural Heritage Department of the University of Padua on behalf of the author of this paragraph. The project aims to propose a 3D reconstruction of the entire forum by following the Extended Matrix (EM) approach [84]. The research purpose consisted of improving the general comprehension of the archaeological remains of the context and creating an online 3D scene accessible on the web. The site of Nora is located on a peninsula on the southwestern coast of Sardinia, about 30 km southwest of Cagliari. The forum, the ancient roman square used as case study for this work, occupies an area of approximately 3500 sqm (including its annexes) in the eastern sector of the ancient city [85]. In order to assess collaborative features offered by the framework, we present in this section outcomes from a multi-user session where 11 users accessed the same 3D scene online, from different physical locations and with different devices. The main goal was to share with multiple participants a guided tour of the 3D reconstruction of the roman forum of Nora, using _Hathor_ front-end (see Section 3.8). The tests aimed to assess the collaborative service during a multi-user session and also to collect a general feedback of the experience. During the tour users had the possibility to freely explore the scene and, most importantly, to interact with each other using their voice and other tools. The virtual scene was composed of 3D models organized in 5 layers (\"Contemporary\", \"Period IV\", \"Period IV rec\", \"Period V\", \"Period V rec\"). The first layer, the base from which the 3D reconstructive proposal was then realized, represents the photogrammetric model of the area (Contemporary layer). The additional 4 layers correspond to the extant archaeological remains (\"Period IV\": red, and \"Period V\": blue), dealing with the two chronological phases analyzed with the project, and their virtual reconstruction (\"Period IV rec\": light red, and \"Period V rec\": light blue). The entire reconstructive proposal of the forum was carried out by using both archaeological, geometric and bibliographic data arranged and linked together following the EM approach. This method allows to map and visually represent the reconstructive process behind a virtual reconstruction of an archaeological context. With the exception of the contemporary layer, a semi-transparent material was used for the volumes of the additional 4 layers. The test consisted in a virtual tour of the forum (see Figure 21) carried out by a guide (one of the users) in the reconstructive proposal, with different collaborative tools offered by Hathor available to participants. Before starting the tour, \"navigation modes\" (see Section 3.6.3) and collaborative tools were introduced to participants to provide all the basics, with a \"virtual guide\" leading the tour in the 3D scene. Hathor offers the ability to enable persistent changes to the scene (see Section 3.8), thus allowing both the guide and all the users to perform modifications in a synchronous manner. During the visit, both basic (spherical) and complex (free-form) annotation shapes were used to record information on the scene. The virtual guide employed basic annotations to \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Device** & **OS** & **GPU** & **avg. FPS** \\ \hline Honor v10 (smartphone) & Android 9.0 & Mali-G51 & 56.3 \\ Huawei MediaPad M5 (table) & Android 8.0 & Mali-G71 & 54.2 \\ Apple iPhone 12 (smartphone) & iOS & Apple GPU & 49.7 \\ PC (workstation) & Windows 10 & NVIDIA GTX 980 & 59.9 \\ Oculus Quest v1 (HMD) & based on Android & Adreno 540 & 66.4 \\ Oculus Quest v2 (HMD) & based on Android & Adreno 650 & 72.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Average framerates (4 min) for each device. signal the different reconstructed structures (temple, monumental accesses, basilica, curia).