## 4 Results  
### Comparison of the Geometry of Models Obtained by Scanning in MeshLab Software  
MeshLab was used for the comparison of geometrical details of two obtained models--the original model and the model with digital error (using 3D laser scanning technique). It can be noticed that 3D models obtained by photogrammetry are visually rougher compared to the 3D models obtained by scanning, and that is the reason for using 3D models obtained with 3D scanning for analysis in MeshLab and survey. The reference mesh was the mesh obtained from the sculpture without the added clay details. Both meshes were imported and aligned in MeshLab to process the quality control of the details on the mesh with a digital error in comparison with the referent original 3D model of the sculpture. The original and the model with the digital error were compared in MeshLab by calculating vertex geometric distance between them, using the filter named Distance from Reference Mesh. First, both models (the original model and the model with a digital error) were imported into MeshLab software (Figure 8). When the models were imported, in order for their geometry to be compared, it was necessary to align their positions and orientations. This step was done using the Align option in the MeshLab software. In this/our case, the reference model is the model obtained by digitizing the original sculpture and the position, and orientation of the second model is aligned with the reference model. When the mentioned model was declared the reference model, and the option of aligning the model based on key/reference points was chosen, it was necessary to set key points on both models (Figure 8b). The key points are placed on the characteristic parts of the face. The reference points must not belong to the \"sculptural error\" zones. It should be emphasized that the points on the basis of which the alignment of the model is made are arbitrarily set/chosen by the user and that the precision and accuracy of the final result depends on the accuracy of the given positions of the same points on both models. The software recognizes key points and performs their pairing on the models based on the index, that is, the ordinal number of the point according to which they are assigned on the model. For example, if a point with index 0 is in the middle of the upper lip on the reference model, the point with the same index must also be in the same position on the model being compared to the reference, as shown in Figure 8b. The process of setting key points is done manually. After the key points are set on both models, they are aligned by calling the Process option. The aligned models are shown in Figure 8c. After the models have been aligned, they are compared, i.e., the vertex geometric distance between them is measured using the Distance from Reference Mesh filter. This filter is automatic and determines the vertex geometric distance on both concave and convex parts of the model geometry. To visually represent the difference/error measured using the Distance from Reference Mesh filter, another filter was used in the MeshLab  
Figure 8: Aligning models in MeshLab software: (**a**) unaligned scanned models imported in MeshLab; (**b**) setting key points on the models for the aligning procedure; (**c**) aligned models. software. This is called Colorize by Vertex Quality, where vertex quality represents the value of the measured geometric distance and based on that value (depending on whether it is positive or negative), the model is colored with the appropriate color. The results of the model comparison are shown in Figure 9.  
The result of the vertex quality for the meshes obtained using the 3D scanning technique is illustrated as the visual representation of the values in Figure 9. The visual representation of the histogram values shows that the details on the models mostly match and do not differ as is illustrated by green values.