# Realization of Impression Evidence with Reverse Engineering and Additive Manufacturing
## 2 Materials and Methods
### Reconstruction of Plastic Footwear Impression  
#### 2.1.1 3D Digital Reconstructions of a Footwear Impression  
A footwear impression was made indoors in a shallow sandbox (0.8 m long, 0.5 m wide and 0.4 m depth) filled with local dry sand under uniform light using a right-side footwear outside (Male, European Size 44) shown in Figure 6. Artificial damage features including scratches, wear, hole and two cuts with different sizes, shapes and complexity were made on the outside before making the impression. Once the impression was created (see Figure 7), it was scanned with the five different non-contact surface scanning systems. Afterwards, the impression was also casted using POP to contrast the 3D reconstruction quality obtained by conventional casting with that obtained by 3D scanning data and its corresponding 3D printed replicas. Handheld 3D Laser Scanning (HandySCAN 307, Vxelements)  
The workflow of 3D reconstruction of footwear impression by laser scanner is illustrated in Figure 8. The outside impression was scanned by HandySCAN 307 (Creaform, Levis, QC, Canada) handheld 3D laser scanner at a resolution of 0.1 mm (see Figure 8a) through capturing 3D data approximately 360\({}^{\circ}\) of the impressions. The scanner was first calibrated prior to scanning using the specific calibration board and the calibration tool within the accompanied Vxelements 10 software. During scanning, the optimal location for the scanner was insured to guarantee a maximum coverage and accuracy through the flashing LED display that changes colors depending on the distance between the scanner and  
Figure 6: The reference footwear. Vertical red arrows refer to the artificial individual characteristics: (**1**) wear, (**2**) hole, (**3**) scratches and (**4**) cut. Horizontal blue arrows refer to class characteristics: (**5**) brand name, (**6**) logo, and (**7**) size. Figure 7: The footwear impression in the sandbox. The white target dots are reflective reference points used by 3D laser scanner to generate 3D coordinates. the impression. After impression was scanned, the accompanied Vxelements (Creaform, QC, CA) software used the captured raw data to generate a high-quality surface mesh model by using powerful surface construction algorithms (see Figure 8b). The final model, after removing surrounding artifacts, was saved in STL format (Figure 8c). The scanning process lasted for 5 min, with an additional processing time of 3 min, and the market price of the scanner starting at USD 21,900. Structured-Light Scanning (EinScan-SP, EXScan S)  
The 3D scan of impression was carried out by using the white-light EinScan-SP 3D scanner (SHINING 3D Tech, Hangzhou, China) at a single-shot accuracy of \(\leq\)0.05 mm. the scanner equipped with 1.3 MP resolution camera and white-led light source and calibrated according to manufacturer instructions before scanning. The scanner was mounted on a custom mount at 700 mm from the impression (Figure 9a). Acquired data were processed using the associated software (EXScan S, Shining 3D) (Figure 9b). The scan was then edited to remove excess data and the final model saved in STL (Figure 9c). The scanning process lasted 20 min, with an additional 8 min needed for processing, and the scanner starts at a price of USD 2199. The workflow of 3D reconstruction of footwear impression by SL scanner illustrated in Figure 9.  
Figure 8: Workflow of footwear impression 3D reconstruction using HandySCAN 307 laser scanner: (**a**) scanning; (**b**) image processing; (**c**) impression model. Figure 9: 3D reconstruction of footwear impression by using the EinScan-SP structured-light scanner: (**a**) scanning; (**b**) image processing; (**c**) impression model. Smartphone Photogrammetry (Samsung A70, Recap Photo)  
The procedure of 3D reconstruction of footwear impression by using Recap Photo photogrammetry is illustrated in Figure 10. The impression was photographed in line with photogrammetry guidelines of Autodesk Recap v2023 Photo web-based professional photogrammetry software (Figure 10a).