Photogrammetry the practice of determining the geometric properties of objects from photographic images. Photogrammetry is as old as modern photography and can be dated to the mid-nineteenth century. Early methods used a perspective grid located in a given photograph to relate a mark or object to another mark or object. The pencil and ruler method was tedious. Now there are computer programs make the process much easier and faster.
Photogrammetry can be employed very effectively in crash reconstruction. When litigation for accidents occur a reconstructionist needs to determine the exact deformation present in the vehicle. Several years may have passed and the only evidence that remains are the scene photographs taken by the police. Photogrammetry is used to determine how much the car in question was deformed in relation to a similar exemplar vehicle. The amount of energy required to produce that deformation can then be determined. The crush energy can then be used to determine important information about the crash like velocity at time of impact.