Technical NoteMulti-camera system for 3D forensic documentation
Introduction
Three-dimensional (3D) surface documentation is well established in the field of forensic documentation. Crime scenes and corpses are scanned using laser scanners or surface scanners with optical 3D cameras, and photogrammetry is an additional documentation tool [1], [2], [3], [4], [5], [6]. The 3D results provide investigators with important additional information in many cases [7], [8], [9], [10]. Some data are used for 3D comparisons between patterned injuries and the presumed injury-causing instruments.
Even in cases with living persons, including suspects and victims, 3D documentation using 3D scanning or photogrammetry is steadily increasing [11], [12]. One example application is the determination of the body stature of a suspected person for the police [12]. At our institute, we also use 3D photogrammetry to document patterned injuries during physical examinations following assaults.
Regardless of the system used, the main difficulty in documenting living persons is movement. Movement may result from respiration, bloodstream motion, shifts in position or balance control [13]. The larger the area to be documented, the greater the influence of movement on the accuracy of the documentation. In rare cases, suspects who are aware of these limitations attempt to interfere with surface scans by moving their facial muscles. Due to the above-mentioned difficulties of documenting living persons, an alternative documenting procedure is needed. This procedure should meet the following requirements: short documentation times (ms rather than s) making the measurements more robust in the presence of motion, the requirement of a low number of scans to capture the whole body, and an accuracy that is comparable to that of existing procedures.
In 2013, the company botspot (botspot GmbH, Berlin, Germany) introduced a 3D documentation system that utilizes synchronized digital multiple single-lens reflex (DSLR) cameras to document the whole body in one shot for the production of 3D prints [14].
This article introduces the botscan© multi-camera system for the forensic markerless photogrammetric whole body 3D surface documentation of living persons in standing posture.
Section snippets
Hardware
The 3D scanning system developed by the botspot company is called botscan©. The system has a modular design and consists of 12 panels forming a cylindrical chamber with a diameter of 3.35 m. One of the panels serves as an entry door. A total of 64 cameras are used, with 60 cameras distributed evenly – five placed vertically on each panel - and four cameras placed on top of the chamber (Fig. 1). This setup allows for 360° recording of any object placed in the center of the cylinder. The cameras
Discussion and conclusion
This technical note reports a system for rapidly generating 360° documentations of persons. The botscan© multi-camera system controlled by the DSLR Remote Pro Multi-Camera© software generates 64 images of a person. The images are processed into textured 3D models using the PhotoScan© software.
Currently used systems, such as laser scanners or surface scanners with optical 3D cameras, only cover parts of the body. To generate a 3D model of the whole body of a person, at least two scans are
Acknowledgements
The authors thank Seraina Meier for support during the system set-up and calibration.
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2019, Forensic Science International