This report describes the technological features and forensic investigative benefits of a 3D imaging system being developed by Dr, Song Zhang at Purdue University with funding from the National Institute of Justice (NIJ), which is anticipated to enable the rapid collection of 3D detail of crime-scene impressions by operators with minimal training in the use of the scanner.
Under current methods for capturing the details of impressions of crime-scene shoe and tire tracks, crime-scene investigators (CSIs) use two-dimensional photography and casting techniques. This results in the quality of the evidence often being limited by the CSI's skill, the quality of the equipment, and available supplies, as well as the time required to capture the impressions. The envisioned 3D imaging system being developed at Purdue University is expected to overcome these challenges. This system is based on optical 3D scanning technology and uses a binary defocusing technique and an auto-exposure control method to produce a detailed 3D model of the impression (a virtual impression). The system can also produce a virtual cast by inverting the data in the virtual impression, which enables examiners to compare the shoe outsole or tire tread to the virtual cast on-screen or generate a physical model using a 3D printer. These virtual items can be manipulated in 3D space by rotating them 360 degrees along any axis. The first-generation scanner will be battery powered and sufficiently light and compact to be as portable as a 2D camera.