What is Photogrammetry?

Photogrammetry is a technique used in surveying to measure the three dimensional coordinates with the help of photography. It is used for the purpose of measurements.

Fundamental Principle
Triangulation is the fundamental principle used by photogrammetry. In this technique, we take photographs from atleast two different locations. The purpose of taking pictures from more than 2 points is to create what engineers call “lines of sight.” Once these lines of sight are prepared, we join them to locate a point where they meet and thus calculate the coordinates of the desired point.

Scale formulas
Photo scale=ab/AB=f/(H-h₁)
where f =focal length of lens, in (m)
H =flying height of airplane above datum (usually mean sea level), ft (m)
h1 =elevation of point, line, or area with respect to datum, ft (m)