Principal plane in photogrammetry: The principal plane is associated with which elements or points of an aerial photograph?

Introduction / Context:
Understanding special points and planes on an aerial photograph is essential for interior and exterior orientation. The “principal plane” is particularly important when a photograph is tilted, as key points lie in this plane along the direction of tilt.

Given Data / Assumptions:

• Single-exposure frame camera.
• Slightly tilted photograph so that principal point and nadir do not coincide.
• Standard definitions from classical photogrammetry.

Concept / Approach:
The principal plane is the plane that contains the principal axis (through the perspective centre normal to the photo plane) and the vertical (plumb) line when the photo is tilted; its intersection with the photograph defines the principal line. Important points such as the principal point, isocentre, and nadir all lie along this plane/line in the direction of tilt.

Step-by-Step Solution:
Principal axis and principal line define the plane’s orientation.On a tilted photograph, the principal point, isocentre (bisector point), and nadir align along the principal line within the principal plane.Therefore, the principal plane is associated with all listed elements.

Verification / Alternative check:
Graphical tilt correction procedures plot principal point, isocentre, and nadir along the principal line; this construction relies on the principal plane geometry.

Why Other Options Are Wrong:
Each element is correctly associated; omitting any gives an incomplete picture of the geometry.

Common Pitfalls:
Assuming principal and nadir points are identical on all photos; they coincide only when tilt is zero.

Final Answer:
All of the above.