Optical 3D-sensors are typically built as stationary measurement systems with a fixed location, e.g. in industrial quality control. The design as a mobile 3D-scanner allows the usage of the system at varying locations, e.g. crime scenes. The project 3D-Forensics, funded by the European Union and supported by forensic experts, focussed on the development of such a 3D-scanner based on fringe projection for the recovery of footwear and tyre traces at crime scenes. This application also requires a high resolution level, because details, such as tiny scratches in a sole of a shoe, often lead to the identification of criminals.
High mobility was achieved by designing the handheld 3D-scanner as a completely self-contained measurement system including an integrated processing unit, operating panel, and batteries. During operation no additional equipment is required. The 3D-sensor captures a field of view of 325 x 200 x 100 mm³ with up to 2.5 Mio. 3D points with a point pitch of 0.17 mm. The high resolution allows the detection of relevant details in impression traces. The 3D-scanner contains a digital camera as an attachable add-on component, which captures a high resolution color image calibrated to the point cloud. This can give additional information in the investigation of the trace. Batteries allow the system to be operated for between 30 and 60 minutes. The scanner is controlled on a touchscreen. The control software was optimized on ease of use. The crime scene investigator adjusts the scan position with the live camera image and selects the optimal exposure time depending on the underground. The scan result is directly presented as a preview. The investigation of the traces is carried out with dedicated software, which allows the analysis of the 3D- and color data. The whole system consisting of 3D-scanner and software was further developed with respect to data integrity issues to enable its usage as evidence in court. The 3D-scanner was tested in cooperation with crime scene investigators in environments similar to real crime scenes. The quality of the scan results was compared to plaster casts, which is the state of the art technique used to recover impression traces. The achieved level of detail through 3D-scanning is similar or even higher. A great advantage in comparison to plaster casting is the contactless and quick capturing of the traces. The benefit of the new handheld 3D-scanner in relation to previous solutions is the combination of high mobility with high data quality. Further application fields besides footwear and tyre traces are other forensic trace types as well as in medicine or archaeology.
Authors: Roland Ramm, Ingo Schmidt, Peter Kühmstedt, Gunther Notni, Max Lucas (Lucas instruments GmbH)