What is Photogrammetry ?

Photogrammetry is defined as the art, science and technology of obtaining reliable information about physical objects and environment through the process of interpreting, measuring and recording.

The word photogrammetry has been derived from three Greek words as follows:
Photo = light; gram = write/sketch; metros=measure.

So, photogrammetry is a process of making some measurement on the surface of photo/ using photograph, where a photograph is a sketch made from light.