This paper describes a device and method that capture 3D images of tire-track and footprint impressions at crime scenes with high fidelity while producing high-resolution 2D color texture images simultaneously.
The design of the 3D impression imaging device is described, along with a prototype built by the authors that includes a calibration method for obtaining the 3D image with the proper metric information. The method provides a depth resolution of about 0.5mm at the shortest zoom settings and even higher resolution at longer zoom settings, along with a high-resolution color image properly registered with the depth image. It can digitize impression evidence that has long spatial spans, such as long tire-track impressions that would be difficult to fit into a single photographic shot. The device is portable, lightweight, and can be used outdoors. A description of the design of the 3D imaging system addresses the hardware setup and image processing algorithms. Other major sections of this paper address system calibration, computing the 3D impression image, and experimental results. The device produces better quality data at a close range obtained in a larger field compared to existing devices. It avoids problems related to occlusions by using two lasers and can digitize long spans of impressions in one scan. The calibration method is integrated into the scanning process on site, thus avoiding problems with pre-calibrated configurations becoming stale during transportation and setup. 6 figures and 11 references