Glossary for Geospatial Science

focal length:� The distance from the lens at which parallel light rays are focused to a point.� Focal length is essentially a measure of the �zoom� level of a camera lens.� Longer focal lengths create a higher zoom level, capture a smaller area of the target scene, and introduce smaller displacement errors.� 6-inch, 8.25-inch, and 12-inch focal lengths are common for aerial photography done by government surveying authorities in the United States.�� Focal length affects the geometry of the photo and must be provided as an input to computational orthoimage and DEM processes.