Close-range photogrammetry for accident reconstruction

Throughout the last decade forensic scientists, technicians and police have employed a number of 3D measurement tools for crime scene and accident reconstruction. These have ranged from the basic, such as EDM instruments, to the complex, namely terrestrial laser scanners. In the field of traffic accide nt reconstruction, close-range photogrammetry is now being adopted, primarily because of the grea tly reduced on-scene time, which leads to shorter periods of traffic disruption. The fact that a permanent visual record is also obtained, from which 3D measurements can be made at a ny time, is a further notable benefit. However, for successful application of close-range photogrammetric techniques in accident reconstruction a few important issues must f irst be dealt with. These include accommodation of the generally very poor, near-planar network geom etry encountered and the need for maximum ease of use, from which follows the requirement for highly automated processing and fully automatic camera calibrat ion. This paper reports upon two innovative developments undertaken to enhance the applicability of close -range photogrammetry and consumer-grade digital cameras to accident reconstruction. The developments comprise a new approach to robust on-line image orientation a nd a method for automatic camera calibration which employs colour coded targets. The y are highlighted via the iWitness system, which has been developed primarily for accident scene r econstruction and forensic measurement applications.