Forensic Photogrammetry

Forensic photogrammetry is a process used in the investigation of a crime scene. Experts make measurements from photographic images, such as video cameras or still cameras, to document an accident or crime scene. The survey of the site improves the measurement accuracy and facilitates the measurement process. It is important that this survey is very accurate.

The object location and size in the picture are determined from single or multiple images of the same frame made from different locations. A multiple view image is better and results in a more accurate measurement; however, these types of images are only available from surveillance systems with multiple cameras or images taken by police forensic investigators.

The objects in the photo are measured from the multiple images using a technique known as phototriangulation. Anything seen from two camera locations forms a triangle. The object is one point of the geometric triangle, while the two cameras each form the second and third points of the figure. Advanced computer graphic techniques are used to measure objects from single images. Virtual objects are inserted into the scene if the photographer knows the dimensions or locations of certain features. This method is often used when examining automobile collisions.

Engineers use photogrammetry during litigation to determine how a car was deformed in a crash. By the time these cases make it to court, several years may have passed; all that is left are the crime scene photos.