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Photogrammetry

Photogrammetry is the science of deducing the physical dimensions of object from measurements taken from imagery. In the forensic field, the most common form of photogrammetry is to make an assessment of an offender's height from CCTV. In general, an assessment of height in the investigative phase following an offence can be useful in order to narrow a list of suspects. From advantageous material, the height of an individual can be calculated to +/- one inch. In general, however, the level of tolerance is somewhat wider, but still sufficient to be helpful in eliminating those outside the bracket.
 
In a broader sense, photogrammetric calculations can be employed to measure any object. Typically footwear, weapons and other physical objects are measured, often as part of a comparative analysis to consider identity.
 
Accurate photogrammetry relies on careful and detailed interpretation, a detailed understanding of geometric distortions, and a thorough understanding of perspective. When measuring height of people, then movement and posture also need to be taken into account, and will impact on the tolerances that apply to the final result.
 
Another related aspect of photogrammetry is determining speeds of vehicles, ships, bicycles etc. Using the framing rate of a recording system, together with measurements taken from the scene, it is usually possible to produce reasonable assessments of speed. In terms of road traffic incidents, we most often work alongside accident investigators to help corroborate their findings.