# Preliminary Application of the Algorithm Highlighting Petroglyph Patterns
## 4 Materials and Methods  
An Artec Eva 3D scanner (Figure 1) was used to scan the petroglyphs in Hodjikent. The Artec Eva is a versatile, high-speed 3D scanner. It is characterised by fast and accurate measurement, precise texture and colour reproduction, high resolution 3D scan and ergonomic design. The Eva scanner has been designed with its user in mind--it is light, does not require the use of positioning markers (glued on the scanned object) or calibration, which significantly improves the comfort of work. The scanner performs scanning using structured light, which makes it completely safe for the scanned monuments. In addition, the recording of 16 frames per second allows to perform quick and accurate scans. The basic parameters of the scanners used are presented in Table 1.  
The data obtained after scanning were processed using the Artec Studio version 12 Professional. This is software dedicated to Artec scanners. \begin{table}
\begin{tabular}{c c} \hline \hline
**General Specification** & **Artec EVA** \\ \hline Working distance & 0.4–1 m \\ Measurement area volume & 61,000 cm\({}^{3}\) \\ Linear field of view H \(\times\) W (min) & 214 mm \(\times\) 148 mm \\ Linear field of view H \(\times\) W (max) & 536 mm \(\times\) 371 mm \\ Angular field of view H \(\times\) W & 30\({}^{\circ}\times 21^{\circ}\) \\
3D resolution, up to & 0.5 mm \\ Accuracy of the 3D point, to & 0.1 mm \\
3D accuracy at a distance, up to & 0.03 \% at 1 m \\ Ability to Capture Texture & Yes \\ Texture Resolution & 1.3 mp \\ Colours & 24 bpp \\ Reconstruction 3D, up to & 16 fps \\ Data download speed, up to & 2 million points per second \\ Structured light source & flash bulb (without laser) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Basic parameters of the Artec Eva scanner. Figure 1: Scanner view: Artec Eva. The petroglyph was subjected to a scanning process, Figure 2. An Artec Eva scanner was used. The Artec Studio version 12 Professional was used for data processing. The first phase of data processing was loading the scanned objects and placing them in three-dimensional space. The loaded objects are shown in Figure 3.  
The superimposition of the scanned objects and their processing made it possible to obtain a 3D mesh model of the petroglyph. A number of activities based on specialised tools were used to build the mesh:  
* Registration--Fine registration. * Edition of scans--Removed artefacts; (selection tools were used, such as: Lasso selection, Cutoff-plane selection and 3D selection). * Alignment of scans--scans were matched by specifying 3-4 pairs of characteristic points on the scans. * Registration--Global registration. * Fusion--Outlier removal. * Fusion--Smooth fusion. * Postprocessing--if there were holes, they were repaired using the Hole filling or Fix holes tools. Figure 3: Sample objects in the form of a petroglyph scan, (**a**) scan no. 1, (**b**) scan no. 2. Figure 2: Petroglyph scanning process. * Postprocessing--Mesh simplification. * Applying texture. The mesh model of the petroglyph generated by the program is shown in Figure 4.  
The mesh model obtained from the scans had the so-called zero thickness. This was due to the fact that the object (petroglyph) was scanned only from one side--from the front. Moreover, the obtained 3D mesh model would be burdened with defects of mesh geometry. Autodesk's 3 ds Max program was used for further processing of the mesh model. With the right tools and Boolean logic operations, the missing areas of the mesh were supplemented and a fully valuable virtual object of the scanned petroglyph was obtained, Figure 5.  
The created object was saved as files with extensions STL and XYZ. The examined petroglyphs were made by subtractive methods. Apart from the drawings themselves, there are many cavities in the investigated rock material. Scanning the surface provides a good quality topographic model, which has the additional consequence of transferring to digital form the grooves.