Basic Concepts of Aerial Photography

          Aerial photography is an image of the real world in to a photograph taken by specific camera build in aircraft. Aerial photography provides a stereoscopic view of the earth surface in vertically and horizontally, it is a three dimensional viewing image.   

Film: Aerial photography missions are flown using black and white film, but colour, infrared, and false colour infrared film are sometimes used for special projects.

Focal length: It is the distance from the middle of the camera lens to the focal plane. As focal length increases, image distortion decreases. The focal length is precisely measured when the camera is calibrated.

Scale: The ratio between two points on an air photo and actual distance between the same two points on the ground.

Aerial Photo Scaling

Calculation of scale

There are a number of methods for calculating scale depending on what information is already known:

•      Focal length and flying height for flat terrain.

•      Focal length and flying height for variable terrain.

•      Photo distance and corresponding map or ground distance.

Calculation of scale

Method 01

If a 1 km stretch of highway covers 4 cm on an air photo, the scale is calculated as follows:

Another method used to determine the scale of a photo is to find the ratio between the camera's focal 

length and the plane's altitude above the ground being photographed.

•      If a camera's focal length is 152 mm, and the plane's altitude Above Ground Level (AGL) is  

7 600 m, using the same equation as above, the scale would be: 

The photo scale and representative fraction 

•      PS  =  f / H
Variables: PS - Photo Scale, f - camera focal length, H - altitude above the ground
Photo Scale is equal to camera focal length divided by the Height (altitude) of the plane.

•      RF = 1/(H / f)
Variables: RF - Representative Fraction, f - camera focal length, H - altitude above the ground Representative Fraction (RF) is equal to one divided by the ratio of altitude (H) and camera focal length.