Dimensioned Air Photos from Various Flights

Dimensioning (calculating actual sizes of features in the photo) of some air photos was done to extract information about the sizes of features. The width and height of the area on the ground captured on film is a function of the focal length of the camera lens and the distance to the ground. These photos have been dimesioned applying the following algorithm:

	

		l = 2d * tan(a/2)
	
		a = tan^-1 (w/(2f))



	l = distance on the ground captured along long axis of the photo (m)

	d = distance from film to object = altitude (m)

	a = angular field of view (degrees)

	f = focal length of camera lens (mm)

	w = width of film = 34.95 mm

This assumes the object plane is at nadir from the film plane (camera is directly overhead, pointing straight down), and that the focal length is vanishingly small compared to (d). In actuality, none of the photos are exactly at nadir (near nadir photos were taken by banking the plane and having the photographer lean farther out of the window).