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 accident reconstruction, close-range photogrammetry is now being adopted, primarily because of the greatly 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 any time, is a further notable benefit. However, for successful application of close-range photogrammetric techniques in accident reconstruction a few important issues must first be dealt with. These include accommodation of the generally very poor, near-planar network geometry encountered and the need for maximum ease of use, from which follows the requirement for highly automated processing and fully automatic camera calibration. 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 and a method for automatic camera calibration which employs colour coded targets. They are highlighted via the iWitness system, which has been developed primarily for accident scene reconstruction and forensic measurement applications.