What is the definition of photographic scale?

Suppose the ground T is a horizontal plane, and the photo remains strictly horizontal during photography. The distance from the projection center S to the plane T is the flight height H; the distance to the image plane P is the camera principal distance f, as shown in Figure 1-1:

The image level and the image in the horizontal flat area Film scale

1/m=f/H?(1-1)

Equation (1-1) indicates that the imaging scale on the camera film is equal to the main distance and the flight angle of the aerial camera. The ratio of height to height, so when the photo is horizontal and the ground is horizontal, the photo scale is a constant.