# Influence of Material on the Density of a Point Cloud Created Using a Structured-Light 3D Scanner
## 3 Materials and Methods
### Methodology of Scanning Results Evaluation (A5, A9, A13)  
To evaluate individual materials, the idea of the so-called ideal material was created. This is a material that we assume is ideal for scanning purposes and which will not create a very sparse point cloud that could result in a poor-quality polygon network [31].  
Based on previous experience with the Artec Eva Lite scanner, we assume that this is a material that has the following properties [11; 32]:  
1. Is not translucent, or in the worst case transparent;
2. Is neither shiny nor reflective;
3. Does not contain very fine elements (hair, fur, fluff, etc.).  
Based on the idea of an ideal material, we can expect that scans of some materials will have enough point cloud density without any surface treatment. We call these materials \"well scannable\". Then, we can recognize material characteristics that by expectation can worsen material scannability and, as a result, decrease point cloud density. These characteristics are as follows:  
1. The material contains very fine elements;
2. The material is glossy;
3. The material is transparent.  
As already mentioned, the point evaluation is based on the criteria of the ideal model given in the previous part of this section. To evaluate each of the criteria, a scale with points 1-10 was chosen, which allows for sufficient variability. Point assessment, which falls under object reconnaissance, was assigned by an expert estimate. The reason for this inclusion is the fact that the determination of the need to modify the material's surfaces before scanning is also determined by expert estimation. If the criterion is unconditionally met, the given object will be awarded the full number of points, i.e., 10. It follows that the ideal material described above should have the full number of points for all criteria. However, if there is partial or complete non-compliance, points are reduced according to the degree of violation. This depends on the degree of violation of the evaluated criteria, that is, the transparency, gloss, and fineness of the texture of the scanned material.  
We used different methods according to the type of material for surface treatment.  
For materials with fine elements, the treatment consisted of smoothing the surface (combing). For glossy and transparent materials, the first treatment consisted of applying a thin layer of matting spray (chalk spray, or dry shampoo) so that the origin surface of the sample was still slightly visible. The second treatment consisted of applying a thicker layer of matting spray (chalk spray, dry shampoo) so that the original surface of the sample was completely covered and not visible.  
The coefficient of variation represents the ratio of the standard deviation to the mean [33]. The coefficient is useful for comparing the degree of variation from one data series to another even if the means are drastically different from one another [34; 35; 36]. Due to the large difference from one another, the coefficient of variation and not the standard deviation was used. The standard deviation measures how far the average value lies from the mean, whereas the coefficient of variation measures the ratio of the standard deviation to the mean [35]. The values of the coefficient of variation were calculated using R version 4.3.1.