# Realization of Impression Evidence with Reverse Engineering and Additive Manufacturing
## 4 Conclusions  
Currently, forensic reconstruction is moving towards digital transformation through the integration of reverse engineering and additive manufacturing technologies for the documentation, analysis, and presentation in the operational methodology. The use of 3D digital and 3D printed impression models in real and enlarged sizes to convey certain observations and findings may provide invaluable resources for detailed explanation of the evidence analysis results in the court, in addition to other forensic educational and forensic related practices. For this reason, it is important to evaluate the potential capabilities and limitations of the available 3D techniques in forensic reconstruction. To date, comprehensive studies on both qualitative and quantitative evaluation and comparing of the geometric quality of impression evidence acquired by different types of 3D scanning systems have been limited. In the first part of this research, five non-destructive 3D scanning technologies involving HandySCAN 3D handheld laser scanner, EinScan-SP structured-light 3D scanner, smartphone photogrammetry, MS Kinect v2 RGB-D camera and iPhone's LiDAR Sensor were qualitatively and quantitatively evaluated for appropriateness in digital reconstruction of 3D forensic impression evidence. In the second part, two methodologies for 3D reconstructions of 2D latent impression and visible impression evidence from a  
Figure 26: FDM-printed models of 2D visible impression of an unknown footwear: footwear impression in blood on white cotton before enhancement (**a**) and after enhancement (**b**) (both adopted from [32], with permission from Elsevier); (**c**) corresponding FDM-printed replica; (**d**) corresponding inverted FDM-printed replica for extra visualization. (Scale bar: 40 mm). single 2D image were proposed. Finally, the FDM additive manufacturing technique was used in building the 3D reconstructed models created from each part. For digital reconstruction of 3D forensic impression evidence, the results reveal that structured-light 3D scanning has provided the highest accuracy to capture full features of the footwear outside impression, highest amount of acquired points, moderate budget, although demonstrated longest acquiring time, with handheld laser scanning being the second system, which provided slightly lower accuracy (max absolute deviation of 0.7 mm and RMS of 0.0684), but with higher cost. Despite the methodological choice of using a ruler to establish the correct scale of the reconstructed 3D model which may introduce limitations in accuracy, SP photogrammetry ranked the third in accuracy as its impression's clarity was less than the laser system with most individual characteristic nature and uniqueness is obvious. However, it is the best in terms of cost, portability maintenance and power requirements which are major concern in low local and low budget forensic agencies. Although accuracy of SP photogrammetry models does not reach the SL and LS accuracies, the rapid development in SP photogrammetry is expected to offer a competitive scanning solution to the structured-light and the high-cost laser scanners in evidence reconstruction. Investigated RGB-D Kinect v2 camera and iPhone LiDAR technologies showed low accuracy in capturing the fine details of the impression with iLiDAR is the most unreliable one with the highest mean, RMS and Min/Max deviation between points at all levels of data percentages. Within the limits of the experiments performed here, this work recommends that both consumer handheld structured-light and laser 3D scanning modalities could be used for routine forensic practice in the recovery of 3D footwear impressions as new standalone/complimentary route to existing conventional casting, videography and 2D photography methods to offer the most persuasive evidence to the footwear examiner. However, SP photogrammetry, for now, offers only a compliment to traditional recovery methods.