# Influence of Material on the Density of a Point Cloud Created Using a Structured-Light 3D Scanner
## 4 Results
### Transparent Materials  
In general, the most problematic group consists of transparent materials. Samples of materials that are partially or completely transparent were selected and subsequently scanned to assess how much this characteristic affects the density of the point cloud. All samples were placed so that there was no other material behind them in the working distance of the scanner that could affect the scanning result. The transparent materials were as follows: transparent holographic foil, clear textured glass, and polycarbonate. The first of the transparent materials is transparent holographic foil. When scanned without any adjustments, it achieved a very low average point cloud density of 10,938 points per sample area. As a treatment, a chalk spray was used for the test for the next attempt, which ensured the opacity of the material. The average density of the point cloud after the first surface treatment increased by more than 800% in the measured area after application. Nevertheless, the average value of the density of the point cloud was still insufficient; therefore, the chalk spray was applied in a thick layer, increasing it by more than 2150% in the measured area. (Figure 12). After the second treatment, 60% of scanning attempts resulted in point clouds with a density of more than 2200 points/cm\({}^{2}\). Also, the average value of the point cloud density was above the threshold. The foil has a smooth surface, so the point arrangement is again reminiscent of some well-scannable materials, but at the same time, there is noticeable point noise below and above its surface level. Figure 13 shows a point cloud made of clear textured glass, which is less transparent than transparent holographic foil but is slightly colored compared to it, which could have affected the density of this point cloud. The density of the point cloud is twice as high as that of transparent holographic foil. The average density of the point cloud is 24,033 points per sample area. As a treatment, a dry shampoo was used for the test for the next attempt, which ensured that the material was opaque. The average density of point clouds after the first surface treatment increased in the measured area by more than 410% after application. Nevertheless, the average value of the density of the point cloud was still insufficient; therefore, the dry shampoo was applied in a thicker layer, increasing it by more than 920% in the measured area. The average value of the point cloud density was above 2200 points/cm\({}^{2}\), but in 20% of scanning activities the resulting point cloud did not reach the threshold. Figure 11: The noise of the point cloud before (**a**) and after (**b**) chalk spray treatment. Figure 12: Meshes from point clouds of transparent holographic foil with the raw surface (**a**) and 1 st treatment (**b**) and 2 nd treatment (**c**) by chalk spray. The last material examined is polycarbonate (Figure 14), which is the least transparent of this group of materials; it is straight, smooth, and colorless. Due to these properties, the average point cloud density of the material in its raw state was 44,346 points in the measured area, which is 4\(\times\) more than the transparent holographic foil and 2\(\times\) more than the clear textured glass. As a treatment, a chalk spray was used for the test for the next attempt, which ensured the opacity of the material. The average point cloud density after the first surface treatment increased in the measured area by more than 415% after application. The average value of the density of the point cloud was already sufficient, but in three cases the resulting point clouds did not reach the 2200 points/cm\({}^{2}\) threshold. As such, we decided to apply the second surface treatment (a thick layer of chalk spray) where the value of point cloud density was above the threshold in the case of all scanning activities. In the case of all materials, the treatments lead to a decrease in the coefficient of variation; see Table 4.