The correct answer is D. All the above.
Parallax is the apparent displacement of an object relative to a background due to a change in the observer’s position. In aerial photography, parallax is caused by the difference in the line of sight between the two camera stations. The parallax of a point on a photograph is therefore due to the ground elevation, flying height, and length of air base.
Ground elevation: The higher the ground elevation, the greater the parallax. This is because the line of sight from the camera to a point on the ground is longer for a higher ground elevation.
Flying height: The higher the flying height, the smaller the parallax. This is because the line of sight from the camera to a point on the ground is shorter for a higher flying height.
Length of air base: The longer the air base, the greater the parallax. This is because the difference in the line of sight between the two camera stations is greater for a longer air base.
Parallax is used in aerial photography to measure the ground elevation, flying height, and length of air base. It is also used to create stereoscopic images, which can be used to create three-dimensional models of the terrain.