Pick up the correct statement from the following: A. The measured stereoscopic base of photographs is obtained by dividing the air base in metres by the mean scale of the photograph B. The difference between the absolute parallax of two points depends upon the difference in their elevations C. The line joining the principal point of a photograph and the transferred principal point of the adjoining photograph, is called stereoscopic base D. All the above

The correct answer is D. All the above.

The measured stereoscopic base of photographs is obtained by dividing the air base in metres by the mean scale of the photograph. The air base is the horizontal distance between the two camera stations. The mean scale is the average of the scales of the two photographs. The difference between the absolute parallax of two points depends upon the difference in their elevations. The absolute parallax of a point is the distance between the two projections of the point on the two photographs. The difference in the elevations of two points is the vertical distance between the two points. The line joining the principal point of a photograph and the transferred principal point of the adjoining photograph, is called stereoscopic base. The principal point is the intersection of the optical axis of the camera with the plane of the photograph. The transferred principal point is the point on the adjoining photograph that is collinear with the principal point of the first photograph.

The stereoscopic base is used to calculate the height of objects in the scene. The absolute parallax is used to calculate the distance of objects in the scene. The line joining the principal point of a photograph and the transferred principal point of the adjoining photograph is used to calculate the relative position of the two photographs.