Determining Crash Data Using Camera Matching Photogrammetric Technique 2001-01-3313

Accident scene photographs contain important information that can be useful in determining how accidents happened. However, dimensions are difficult to gather from photographs. The size of an object in the photographs depends on how far away from the camera the object is located. An object in the background looks smaller and will measure smaller than the same size object in the foreground. This phenomenon is called perspective distortion.

Photogrammetry was introduced in the late 1800's as a tool to compensate for the perspective distortion and assist in gathering dimensions from photographs. One of the early techniques was to create a transparent miniature of a photograph and place the miniature in the view screen on the camera. The camera was then taken to the scene and matched to the correct position such that the image in the scene matched the image in the view screen. Today, using computer modeling software, a scene can be created in the computer model that matches the actual photograph. Using a technique called camera matching, the camera in the computer can be adjusted to match the photograph. Once properly matched, dimensions within the photograph can be gathered. This technique is useful in gathering dimensional data from crash scene photographs like the point of impact and the point of rest of crash vehicles. Once the crash scene dimensions are determined, the accident can be reconstructed using the principals of conservation of momentum and energy.