## 2 Methodologies
### Extended Matrix  
One of the main goals of the e-Archeo project was to ensure the transparency, durability, and queryability of virtual reconstructions. To achieve this, a formal language was used that could guarantee the scientific mapping of virtual reconstructions. This methodology, called the Extended Matrix, was devised at CNR-ISPC [7]. This tool allows data to be organised so that the different stages of the reconstruction process are transparent and scientifically complete, offering a standardised workflow and a set of tools for data analysis and visualisation.  
The reconstruction hypothesis is based primarily on the study and investigation of the existing data and archaeological research, relying on finding comparative case studies, iconography, and literary sources, when the preserved elements do not provide sufficient information. All the documents used were then organised into a file to be used within the Extended Matrix [8]. Starting from the concept of the Harris matrix, the Extended Matrix proposes an extended version, including information related to the reconstruction. Virtual stratigraphic units are added to the traditional stratigraphic units, to which a specific colour is assigned based on the degree of certainty about their existence as follows [9]:  
* red for preserved and/or documented archaeological remains;
* blue to identify virtual restorations derived from physical evidence;
* dark yellow for elements that were not found in situ and have been repositioned and light yellow for the anastylosis of missing parts;
* green to identify elements reconstructed without physical evidence but based on deductive processes.  
For each virtual unit inside the matrix created with the yEd software, the documents used to arrive at the hypothesis are directly linked through nodes, specifying for which property (geometry, material, position, etc.) they were consulted (Figure 5). yEd [10] is a free desktop application used to quickly create, import, edit, and automatically arrange diagrams. Each stratigraphic unit is represented here, and a reference is linked to it in media format or in the form of a citation. The diagram created in yEd, using a specific palette [11], regulates the representation and succession of shapes in Blender and is, in fact, the heart of the Extended Matrix system.  
Figure 4: “Campo delle Noci”, Grotte di Catullo, Sirmione. Three-dimensional mesh and positioning of the photographs taken by drone (�emezzo.biz).  
Separately, the creation of a virtual model was carried out using the open-source software Blender [12]. The digital replicas of the site, as described in the previous paragraph, were imported into the software, and the reconstruction was modelled on top of them, allowing a perfect overlay between the real and virtual [13]. In this phase, the reconstruction model is characterised by a low-poly geometry, where the architectural structures are reconstructed using simplified volumes. Through a specific add-on developed for Blender [11], the graph of the Extended Matrix is connected to the simplified model, which inherits the semantic code and the source information described above (Figure 6).  
Figure 5: Extended Matrix of Cryptoporticus created in yEd (Grotte di Catullo, Sirmione) ([PERSON]).  
Figure 6: Blender workspace of the cryptorticus (Grotte di Catullo, Sirmione) ([PERSON]).  
In this way, simply by selecting the desired element, specific information on the reconstruction hypothesis made and a direct reference to the sources used to validate the hypothesis itself can be obtained.