This report addresses the features and potential outcomes of a project with the goal of developing a 3D imaging system to overcome current challenges of two-dimensional photographic and casting techniques for recording shoeprints and tire tracks in deformable substrate at crime scenes.
Under these current methods, the quality of the evidence obtained is often limited by the crime-scene investigator’s (CSI’s) skill, the quality of the equipment used, the available supplies, and time constraints. In addressing these challenges, Dr. Song Zhang at Purdue University is developing a 3D imaging system based on optical 3D scanning technology that uses a binary defocusing technique and an auto-exposure control method to produce a detailed 3D model of the impression (a virtual impression). The virtual impression will enable lab analysts to conduct a virtual examination of impressions based on clear and accurate visual records of shoe and tire impressions at the crime scene. The system can also produce a virtual cast by inverting the data in the virtual impression, so examiners can directly compare the shoe outsole or tire tread to the virtual cast on-screen or produce a physical model using a 3D printer. These virtual items of evidence can be manipulated in 3D space by rotating them 360 degrees along any axis. Hardware automation and intuitive graphical user interface enable ease of use. The first-generation device will be battery powered and appropriate in size and weight for easy handling in the field, much like a 2D camera. One 3D scan takes 10 seconds and eliminates having to take multiple camera shots followed by casting. A prototype system, parent pending, was designed to capture an area of approximately 14” x 10” with a spatial resolution of about 140 ppi. The next generation device is expected to improve spatial resolution to 400 ppi.