## 3 Materials and Methods
### Digitization Process
#### 3.2.1 Photogrammetry Surveying  
The equipment used for shooting: tripod and NIKON D7000 camera (pixel size--4.78 \(\upmu\)m, sensor size--23.6 \(\times\) 15.6 mm, focal length range--18-109 mm, and crop factor--1.53), with manual settings of the following parameters: f-stop, ISO speed, exposure time.  
The selected ground sample distance (GSD) value is 0.1 mm because the 0.1 mm details on the object should be visible. The covered space (D) in the photos is determined by considering the number of pixels of the camera:  
\[\text{D}=\text{pixel number}\times\text{GSD} \tag{1}\]  
In that case, the covered space is (0.1 mm\(\cdot\)4928) = 492.8 mm (portrait mode) and (0.1 mm\(\cdot\)3275) = 327.5 mm (landscape mode). Landscape mode was used for the shooting. When GSD was determined, the scale (m) was calculated  
\[\text{m}=\text{GSD}/(\text{pixel size})=0.1/(4.78\times 10^{3})=0.0209\times 10^{ -3} \tag{2}\]  
and the camera distance from the subject (h) is  
\[\text{h}=\text{m}\times\text{c}=0.0209\times 10^{-3}\times 35=0.735\text{ m} \tag{3}\]  
where the focal length (c) is 35 mm.  
The radial distance from the camera to the sculpture should be the same on all sides. The total circumference of the circle is \(2\pi\pi=2\times 0.735\times 3.14=4.615\text{ m}\), so for a \(15^{\circ}\) shift, the distance between the photos is the length of the circle tendon b = 19 cm.  
The final camera distance was set at 0.5 m, so a compromise was made between field of view (FoV) and depth of field (DoF). To provide the required level of coverage of all surfaces of the sculpture with photographs, the photographs were taken in four different stripes in height, with an increment of \(20^{\circ}\). In the face region, the turning increment was less than the predicted \(20^{\circ}\). In Figure 2, four camera positions, denoted \(C_{1}\),...,are shown, and the distances along the optical axis from the camera to the sculpture are indicated, respectively, by \(h_{1},\ldots,h_{4}\). The first stripe is also the lowest stripe in which the camera was placed. The second stripe was set up to photograph the pedestal. At the third level, the camera is positioned at the level of the face with an optical axis of \(90^{\circ}\) relative to the axis of rotation, and at the fourth and highest level, the camera is positioned above the sculpture, so that the optical axis closed a sharp angle (\(\alpha_{4}\)) with the axis of rotation of the turntable. Additional photographs in the region of the face and the crown of the head were taken to gather as much information as possible from the surface of the object. After the photographing, 100 photographs were used to create the 3D model in the AgiSoft Metashape software [71]. The calculated parameters for photogrammetry surveying are shown in Table 1.  
Based on the presented shooting plan, the digitized sculpture was photographed in June 2020. The overview of the shooting plan is shown in Figure 2.  
Figure 3 shows the interior where the original sculpture was photographed, located in the laboratory at the Faculty of Technical Sciences in Novi Sad. Figure 3 shows the markers positioned on a turntable. These markers create two orthogonal lines, which are coordinate axes in the horizontal plane.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Surveying Parameters** & **Original Sculpture and** \\  & **Sculpture with Clay Details** \\ \hline GSD & 0.1 mm \\ D & 0.33 m \\ h & 0.5 m \\ b & 0.19 m \\ Focal length (c) & 35 mm \\ Focus point & 0.7 m \\ f-stop & f/11 \\ ISO speed & 100 \\ Exposure time & 1/2 s \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters for photogrammetry surveying.  
Figure 2: Overview of the shooting plan in the laboratory: (**a**) sketch of the shooting plan; (**b**) realistic set-up of elements in the laboratory.  
Figure 4 shows the results of the photogrammetric survey. While Figure 4a shows the original model, Figure 4b shows the model with the built-in digital error where the red rectangles indicate the parts of the face to which the clay was added.